Patent Publication Number: US-9852163-B2

Title: Methods and apparatus to de-duplicate impression information

Description:
RELATED APPLICATIONS 
     This patent claims priority to U.S. Provisional Patent Application Ser. No. 61/922,090, filed Dec. 30, 2013. The entirety of U.S. Provisional Patent Application Ser. No. 61/922,090 is incorporated herein by reference. 
    
    
     FIELD OF THE DISCLOSURE 
     The present disclosure relates generally to monitoring media and, more particularly, to methods and apparatus to de-duplicate impression information. 
     BACKGROUND 
     Traditionally, audience measurement entities determine audience engagement levels for media programming based on registered panel members. That is, an audience measurement entity enrolls people who consent to being monitored into a panel. The audience measurement entity then monitors those panel members to determine media programs (e.g., television programs or radio programs, movies, DVDs, etc.) exposed to those panel members. In this manner, the audience measurement entity can determine exposure measures for different media content based on the collected media measurement data. 
     Techniques for monitoring user access to Internet resources such as web pages, advertisements and/or other content has evolved significantly over the years. Some known systems perform such monitoring primarily through server logs. In particular, entities serving content on the Internet can use known techniques to log the number of requests received for their content at their server. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  depicts an example system that may be used to determine advertisement viewership using distributed demographic information. 
         FIG. 2  depicts an example system that may be used to associate advertisement exposure measurements with user demographic information based on demographics information distributed across user account records of different web service providers. 
         FIG. 3  is a communication flow diagram of an example manner in which a web browser can report impressions to servers having access to demographic information for a user of that web browser. 
         FIG. 4  depicts an example ratings entity impressions table showing quantities of impressions to monitored users. 
         FIG. 5  depicts an example campaign-level age/gender and impression composition table generated by a database proprietor. 
         FIG. 6  depicts another example campaign-level age/gender and impression composition table generated by a ratings entity. 
         FIG. 7  depicts an example combined campaign-level age/gender and impression composition table based on the composition tables of  FIGS. 5 and 6 . 
         FIG. 8  depicts an example age/gender impressions distribution table showing impressions based on the composition tables of  FIGS. 5-7 . 
         FIG. 9  is a flow diagram representative of example machine readable instructions that may be executed to identify demographics attributable to impressions. 
         FIG. 10  is a flow diagram representative of example machine readable instructions that may be executed by a client computer to route beacon requests to web service providers to log impressions. 
         FIG. 11  is a flow diagram representative of example machine readable instructions that may be executed by a panelist monitoring system to log impressions and/or redirect beacon requests to web service providers to log impressions. 
         FIG. 12  is a flow diagram representative of example machine readable instructions that may be executed to dynamically designate preferred web service providers from which to request demographics attributable to impressions. 
         FIG. 13  depicts an example system that may be used to determine advertising exposure based on demographic information collected by one or more database proprietors. 
         FIGS. 14A and 14B  collectively show a flowchart representative of example machine readable instructions that may be executed to implement the example audience measurement system of  FIG. 13  to de-duplicate audience and/or impressions received from multiple database proprietors. 
         FIG. 15  is a table illustrating an example universe estimate that may be used by the audience measurement system of  FIG. 13  to determine advertising exposure. 
         FIG. 16  is a table illustrating example aggregate audience and impression data from a first database proprietor of multiple database proprietors that may be used by the audience measurement system of  FIG. 13  to determine advertising exposure. 
         FIG. 17  is a table illustrating example aggregate audience and impression data from a second database proprietor of multiple database proprietors that may be used by the audience measurement system of  FIG. 13  to determine advertising exposure. 
         FIG. 18  is a table illustrating example audience level proportions for multiple database proprietors that may be used by the audience measurement system of  FIG. 13  to de-duplicate impression information received from multiple database proprietors. 
         FIG. 19  is a table illustrating example total audience and impression data from multiple database proprietors. 
         FIG. 20  is a table illustrating example correlation and duplicate impression information determined by the audience measurement system of  FIG. 13  using the Danaher method. 
         FIG. 21  is a table illustrating example duplicate reach, duplicate audience, and duplicate impression information determined by the audience measurement system of  FIG. 13  using a random duplication approach. 
         FIG. 22  is a table illustrating example unduplicated impression information determined by the audience measurement system of  FIG. 13 . 
         FIG. 23  is an example processor system that can be used to execute the example instructions of  FIGS. 9, 10, 11, 12, and 14A-14B  to implement the example impression monitor system, the example rules/ML engine, the example HTTP server communication interface, the example publisher/campaign/user target database, the example GRP report generator, the example panel collection platform, the example collector, the example loader, the example ratings entity database, the example panelist computers, the example client computers, the example impression monitor, the example data collector, the example data processor, the example duplication estimator, and/or the example de-duplicator disclosed herein. 
     
    
    
     DETAILED DESCRIPTION 
     Although the following discloses example methods, apparatus, systems, and articles of manufacture including, among other components, firmware and/or software executed on hardware, it should be noted that such methods, apparatus, systems, and articles of manufacture are merely illustrative and should not be considered as limiting. For example, it is contemplated that any or all of these hardware, firmware, and/or software components could be embodied exclusively in hardware, exclusively in firmware, exclusively in software, or in any combination of hardware, firmware, and/or software. Accordingly, while the following describes example methods, apparatus, systems, and articles of manufacture, the examples provided are not the only ways to implement such methods, apparatus, systems, and articles of manufacture. 
     Techniques for monitoring user access to Internet resources such as web pages, advertisements and/or other content has evolved significantly over the years. At one point in the past, such monitoring was done primarily through server logs. In particular, entities serving content on the Internet would log the number of requests received for their content at their server. Basing Internet usage research on server logs is problematic for several reasons. For example, server logs can be tampered with either directly or via zombie programs which repeatedly request content from the server to increase the server log counts. Secondly, content is sometimes retrieved once, cached locally and then repeatedly viewed from the local cache without involving the server in the repeat viewings. Server logs cannot track these views of cached content. Thus, server logs are susceptible to both over-counting and under-counting errors. 
     The inventions disclosed in Blumenau, U.S. Pat. No. 6,108,637, fundamentally changed the way Internet monitoring is performed and overcame the limitations of the server side log monitoring techniques described above. For example, Blumenau disclosed a technique wherein Internet content to be tracked is tagged with beacon instructions. In particular, monitoring instructions are associated with the HTML of the content to be tracked. When a client requests the content, both the content and the beacon instructions are downloaded to the client. The beacon instructions are, thus, executed whenever the content is accessed, be it from a server or from a cache. 
     The beacon instructions cause monitoring data reflecting information about the access to the content to be sent from the client that downloaded the content to a monitoring entity. Typically, the monitoring entity is an audience measurement entity that did not provide the content to the client and who is a trusted third party for providing accurate usage statistics (e.g., The Nielsen Company, LLC). Advantageously, because the beaconing instructions are associated with the content and executed by the client browser whenever the content is accessed, the monitoring information is provided to the audience measurement company irrespective of whether the client is a panelist of the audience measurement company. 
     It is important, however, to link demographics to the monitoring information. To address this issue, the audience measurement company establishes a panel of users who have agreed to provide their demographic information and to have their Internet browsing activities monitored. When an individual joins the panel, they provide detailed information concerning their identity and demographics (e.g., gender, race, income, home location, occupation, etc.) to the audience measurement company. The audience measurement entity sets a cookie on the panelist computer that enables the audience measurement entity to identify the panelist whenever the panelist accesses tagged content and, thus, sends monitoring information to the audience measurement entity. 
     Since most of the clients providing monitoring information from the tagged pages are not panelists and, thus, are unknown to the audience measurement entity, it is necessary to use statistical methods to impute demographic information based on the data collected for panelists to the larger population of users providing data for the tagged content. However, panel sizes of audience measurement entities remain small compared to the general population of users. Thus, a problem is presented as to how to increase panel sizes while ensuring the demographics data of the panel is accurate. 
     There are many database proprietors operating on the Internet. These database proprietors provide services to large numbers of subscribers. In exchange for the provision of the service, the subscribers register with the proprietor. As part of this registration, the subscribers provide detailed demographic information. Examples of such database proprietors include social network providers such as Facebook, Myspace, etc. These database proprietors set cookies on the computers of their subscribers to enable the database proprietor to recognize the user when they visit their website. 
     The protocols of the Internet make cookies inaccessible outside of the domain (e.g., Internet domain, domain name, etc.) on which they were set. Thus, a cookie set in the amazon.com domain is accessible to servers in the amazon.com domain, but not to servers outside that domain. Therefore, although an audience measurement entity might find it advantageous to access the cookies set by the database proprietors, they are unable to do so. 
     In view of the foregoing, an audience measurement company would like to leverage the existing databases of database proprietors to collect more extensive Internet usage and demographic data. However, the audience measurement entity is faced with several problems in accomplishing this end. For example, a problem is presented as to how to access the data of the database proprietors without compromising the privacy of the subscribers, the panelists, or the proprietors of the tracked content. Another problem is how to access this data given the technical restrictions imposed by the Internet protocols that prevent the audience measurement entity from accessing cookies set by the database proprietor. Examples disclosed herein solve these problems by extending the beaconing process to encompass partnered database proprietors and by using such partners as interim data collectors. 
     Examples disclosed herein accomplish this task by responding to beacon requests from clients (who may not be a member of an audience member panel and, thus, may be unknown to the audience member entity) accessing tagged content by redirecting the client from the audience measurement entity to a database proprietor such as a social network site partnered with the audience member entity. The redirection initiates a communication session between the client accessing the tagged content and the database proprietor. The database proprietor (e.g., Facebook) can access any cookie it has set on the client to thereby identify the client based on the internal records of the database proprietor. In the event the client is a subscriber of the database proprietor, the database proprietor logs the impression in association with the demographics data of the client and subsequently forwards the log to the audience measurement company. In the event the client is not a subscriber of the database proprietor, the database proprietor redirects the client to the audience measurement company. The audience measurement company may then redirect the client to a second, different database proprietor that is partnered with the audience measurement entity. That second proprietor may then attempt to identify the client as explained above. This process of redirecting the client from database proprietor to database proprietor can be performed any number of times until the client is identified and the content exposure logged, or until all partners have been contacted without a successful identification of the client. The redirections all occur automatically so the user of the client is not involved in the various communication sessions and may not even know they are occurring. 
     The partnered database proprietors provide their logs and demographic information to the audience measurement entity which then compiles the collected data into statistical reports accurately identifying the demographics of persons accessing the tagged content. Because the identification of clients is done with reference to enormous databases of users far beyond the quantity of persons present in a conventional audience measurement panel, the data developed from this process is extremely accurate, reliable and detailed. 
     Significantly, because the audience measurement entity remains the first leg of the data collection process (e.g., receives the request generated by the beacon instructions from the client), the audience measurement entity is able to obscure the source of the content access being logged as well as the identity of the content itself from the database proprietors (thereby protecting the privacy of the content sources), without compromising the ability of the database proprietors to log impressions for their subscribers. Further, the Internet security cookie protocols are complied with because the only servers that access a given cookie are associated with the Internet domain (e.g., Facebook.com) that set that cookie. 
     Examples disclosed herein can be used to determine content impressions, advertisement impressions, content exposure, and/or advertisement exposure using demographic information, which is distributed across different databases (e.g., different website owners, service providers, etc.) on the Internet. Not only do examples disclosed herein enable more accurate correlation of Internet advertisement exposure to demographics, but they also effectively extend panel sizes and compositions beyond persons participating in the panel of an audience measurement entity and/or a ratings entity to persons registered in other Internet databases such as the databases of social medium sites such as Facebook, Twitter, Google, etc. This extension effectively leverages the content tagging capabilities of the ratings entity and the use of databases of non-ratings entities such as social media and other websites to create an enormous, demographically accurate panel that results in accurate, reliable measurements of exposures to Internet content such as advertising and/or programming. 
     In illustrated examples disclosed herein, advertisement exposure is measured in terms of online Gross Rating Points. A Gross Rating Point (GRP) is a unit of measurement of audience size that has traditionally been used in the television ratings context. It is used to measure exposure to one or more programs, advertisements, or commercials, without regard to multiple exposures of the same advertising to individuals. In terms of television (TV) advertisements, one GRP is equal to 1% of TV households. While GRPs have traditionally been used as a measure of television viewership, examples disclosed herein develop online GRPs for online advertising to provide a standardized metric that can be used across the Internet to accurately reflect online advertisement exposure. Such standardized online GRP measurements can provide greater certainty to advertisers that their online advertisement money is well spent. It can also facilitate cross-medium comparisons such as viewership of TV advertisements and online advertisements. Because the examples disclosed herein associate viewership measurements with corresponding demographics of users, the information collected by examples disclosed herein may also be used by advertisers to identify segments reached by their advertisements and/or to target particular markets with future advertisements. 
     Traditionally, audience measurement entities (also referred to herein as “ratings entities”) determine demographic reach for advertising and media programming based on registered panel members. That is, an audience measurement entity enrolls people that consent to being monitored into a panel. During enrollment, the audience measurement entity receives demographic information from the enrolling people so that subsequent correlations may be made between advertisement/media exposure to those panelists and different demographic markets. Unlike traditional techniques in which audience measurement entities rely solely on their own panel member data to collect demographics-based audience measurement, examples disclosed herein enable an audience measurement entity to share demographic information with other entities that operate based on user registration models. As used herein, a user registration model is a model in which users subscribe to services of those entities by creating an account and providing demographic-related information about themselves. Sharing of demographic information associated with registered users of database proprietors enables an audience measurement entity to extend or supplement their panel data with substantially reliable demographics information from external sources (e.g., database proprietors), thus extending the coverage, accuracy, and/or completeness of their demographics-based audience measurements. Such access also enables the audience measurement entity to monitor persons who would not otherwise have joined an audience measurement panel. Any entity having a database identifying demographics of a set of individuals may cooperate with the audience measurement entity. Such entities may be referred to as “database proprietors” and include entities such as Facebook, Google, Yahoo!, MSN, Twitter, Apple iTunes, Experian, etc. 
     Examples disclosed herein may be implemented by an audience measurement entity (e.g., any entity interested in measuring or tracking audience exposures to advertisements, content, and/or any other media) in cooperation with any number of database proprietors such as online web services providers to develop online GRPs. Such database proprietors/online web services providers may be social network sites (e.g., Facebook, Twitter, MySpace, etc.), multi-service sites (e.g., Yahoo!, Google, Experian, etc.), online retailer sites (e.g., Amazon.com, Buy.com, etc.), and/or any other web service(s) site that maintains user registration records. 
     To increase the likelihood that measured viewership is accurately attributed to the correct demographics, examples disclosed herein use demographic information located in the audience measurement entity&#39;s records as well as demographic information located at one or more database proprietors (e.g., web service providers) that maintain records or profiles of users having accounts therewith. In this manner, examples disclosed herein may be used to supplement demographic information maintained by a ratings entity (e.g., an audience measurement company such as The Nielsen Company of Schaumburg, Ill., United States of America, that collects media exposure measurements and/or demographics) with demographic information from one or more different database proprietors (e.g., web service providers). 
     The use of demographic information from disparate data sources (e.g., high-quality demographic information from the panels of an audience measurement company and/or registered user data of web service providers) results in improved reporting effectiveness of metrics for both online and offline advertising campaigns. Example techniques disclosed herein use online registration data to identify demographics of users and use server impression counts, tagging (also referred to as beaconing), and/or other techniques to track quantities of impressions attributable to those users. Online web service providers such as social networking sites (e.g., Facebook) and multi-service providers (e.g., Yahoo!, Google, Experian, etc.) (collectively and individually referred to herein as online database proprietors) maintain detailed demographic information (e.g., age, gender, geographic location, race, income level, education level, religion, etc.) collected via user registration processes. An impression corresponds to a home or individual having been exposed to the corresponding media content and/or advertisement. Thus, an impression represents a home or an individual having been exposed to an advertisement or content or group of advertisements or content. In Internet advertising, a quantity of impressions or impression count is the total number of times an advertisement or advertisement campaign has been accessed by a web population (e.g., including number of times accessed as decreased by, for example, pop-up blockers and/or increased by, for example, retrieval from local cache memory). 
     In examples disclosed herein, multiple database proprietors collect impression information associated with a same impression. The multiple database proprietors provide the impression information to an audience measurement system. When using multiple database proprietors to collect impression information, a number of reported unique audience members and/or impressions may be duplicated (e.g., reported by both database proprietors). Duplication of impression information results in a single impression being logged in the data as multiple impressions. Due to the duplication of audience members and/or impressions between different data providers, a total audience and/or total number of impressions cannot be accurately determined simply by adding the data from the two database proprietors. Additionally, duplication is not necessarily uniform across demographic groups and, therefore, can result in an inaccurate distribution of demographic groups being reported for the media. Examples disclosed herein de-duplicate the impression information by subtracting the unique audience and/or impressions that have been duplicated from the total unique audience and/or total impressions determined from the multiple database proprietors. Examples disclosed herein perform de-duplication of the unique audience and/or impressions by employing an approach similar to the Danaher de-duplication approach. 
     As used herein, the “audience” of a designated item of media refers to the number of persons who have viewed the designated item of media. An “audience member” of an audience refers to an individual person within the audience. Whereas the calculation of the audience of a media item may, in some circumstances discussed herein, count a single audience member multiple times, the “unique audience” of an item of media is an audience of the item of media each audience members is represented only once. 
     Danaher, P. J., 1991 (“A Canonical Expansion Model for Multivariate. Media Exposure Distributions: A Generalization of the ‘Duplication of Viewing Law.’” Journal of Marketing Research 28(361-367)) proposed a two-vehicle model for estimating duplication probability (p 12 ) as shown in Equation 1 below. 
                     p   12     =       p   1     ⁢       p   2     ⁡     (     1   +     ρ   ⁢         (     1   -     p   1       )     ⁢     (     1   -     p   2       )               p   1     ⁡     (     1   -     p   1       )       ⁢       p   2     ⁡     (     1   -     p   2       )                 )                 Equation   ⁢           ⁢   1               
In Equation 1 above, p 1  is the marginal probability of exposure to a first media vehicle, p 2  is the marginal probability of exposure to a second media vehicle, and ρ (rho) is the correlation (e.g., proportion of overlap) between the first and second media vehicles. As applied to media and impression measurement, the probabilities p 1  and p 2  are synonymous with the reach of the first and second media vehicles.
 
     Methods and apparatus disclosed herein modify the Danaher method to de-duplicate impression information without comparing the impression information at the impression level, which would require large amounts of computing resources. In some such examples, the first and second media vehicles of Danaher are replaced with the first and second database proprietors. Some such examples determine the reach of the first and second database proprietors by identifying cookies associated with the first and/or second database proprietors and determining a proportion of computers (e.g., panelist computers) that have stored cookies for both the first and second database proprietors (as opposed to cookies for only the first database proprietor, only the second database proprietor, or neither of the database proprietors). 
     Examples disclosed herein calculate duplicate reach (p 12 ) as a function of random duplication (i.e., p 1 p 2 ) multiplied by a factor (1+k), where k is determined according to Equation 2 below. 
     
       
         
           
             
               
                 
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     While disclosed examples are described herein with reference to two database proprietors, the examples may be expanded or otherwise modified to accommodate more than two database proprietors. 
     Examples disclosed herein can be efficiently applied using known values of p 1  and p 2  (e.g., the online reach from the database proprietors). By estimating the correlation or proportion of overlap (e.g., ρ) between the chosen database proprietors, examples disclosed herein may be efficiently and rapidly applied to de-duplicate the reported audiences. Example methods and apparatus disclosed herein can be applied in real-time to incoming data, and may be used to determine audience or impression information for any desirable time period (e.g., hourly, daily, weekly, monthly, etc.) and/or cumulatively. Examples disclosed herein may use aggregated audience information as input. As a result, the impression and/or audience information does not need to be processed at an individual impression level or respondent level. Furthermore, examples disclosed herein can be scaled to accommodate any number of database proprietors. 
       FIG. 1  depicts an example system  100  that may be used to determine media exposure (e.g., exposure to content and/or advertisements) based on demographic information collected by one or more database proprietors. “Distributed demographics information” is used herein to refer to demographics information obtained from at least two sources, at least one of which is a database proprietor such as an online web services provider. In the illustrated example, content providers and/or advertisers distribute advertisements  102  via the Internet  104  to users that access websites and/or online television services (e.g., web-based TV, Internet protocol TV (IPTV), etc.). The advertisements  102  may additionally or alternatively be distributed through broadcast television services to traditional non-Internet based (e.g., RF, terrestrial or satellite based) television sets and monitored for viewership using the techniques described herein and/or other techniques. Websites, movies, television and/or other programming is generally referred to herein as content. Advertisements are typically distributed with content. Traditionally, content is provided at little or no cost to the audience because it is subsidized by advertisers who pay to have their advertisements distributed with the content. 
     In the illustrated example, the advertisements  102  may form one or more ad campaigns and are encoded with identification codes (e.g., metadata) that identify the associated ad campaign (e.g., campaign ID), a creative type ID (e.g., identifying a Flash-based ad, a banner ad, a rich type ad, etc.), a source ID (e.g., identifying the ad publisher), and a placement ID (e.g., identifying the physical placement of the ad on a screen). The advertisements  102  are also tagged or encoded to include computer executable beacon instructions (e.g., Java, javascript, or any other computer language or script) that are executed by web browsers that access the advertisements  102  on, for example, the Internet. Computer executable beacon instructions may additionally or alternatively be associated with content to be monitored. Thus, although this disclosure frequently speaks in the area of tracking advertisements, it is not restricted to tracking any particular type of media. On the contrary, it can be used to track content or advertisements of any type or form in a network. Irrespective of the type of content being tracked, execution of the beacon instructions causes the web browser to send an impression request (e.g., referred to herein as beacon requests) to a specified server (e.g., the audience measurement entity). The beacon request may be implemented as an HTTP request. However, whereas a transmitted HTML request identifies a webpage or other resource to be downloaded, the beacon request includes the audience measurement information (e.g., ad campaign identification, content identifier, and/or user identification information) as its payload. The server to which the beacon request is directed is programmed to log the audience measurement data of the beacon request as an impression (e.g., an ad and/or content impressions depending on the nature of the media tagged with the beaconing instruction). 
     In some example implementations, advertisements tagged with such beacon instructions may be distributed with Internet-based media content including, for example, web pages, streaming video, streaming audio, IPTV content, etc. and used to collect demographics-based impression data. As noted above, methods, apparatus, and/or articles of manufacture disclosed herein are not limited to advertisement monitoring but can be adapted to any type of content monitoring (e.g., web pages, movies, television programs, etc.). Example techniques that may be used to implement such beacon instructions are disclosed in Blumenau, U.S. Pat. No. 6,108,637, which is hereby incorporated herein by reference in its entirety. 
     Although exampled are disclosed herein as using beacon instructions executed by web browsers to send beacon requests to specified impression collection servers, the examples disclosed herein may additionally collect data with on-device meter systems that locally collect web browsing information without relying on content or advertisements encoded or tagged with beacon instructions. In such examples, locally collected web browsing behavior may subsequently be correlated with user demographic data based on user IDs as disclosed herein. 
     The example system  100  of  FIG. 1  includes a ratings entity subsystem  106 , a partner database proprietor subsystem  108  (implemented in this example by a social network service provider), other partnered database proprietor (e.g., web service provider) subsystems  110 , and non-partnered database proprietor (e.g., web service provider) subsystems  112 . In the illustrated example, the ratings entity subsystem  106  and the partnered database proprietor subsystems  108 ,  110  correspond to partnered business entities that have agreed to share demographic information and to capture impressions in response to redirected beacon requests as explained below. The partnered business entities may participate to advantageously have the accuracy and/or completeness of their respective demographic information confirmed and/or increased. The partnered business entities also participate in reporting impressions that occurred on their websites. In the illustrated example, the other partnered database proprietor subsystems  110  include components, software, hardware, and/or processes similar or identical to the partnered database proprietor subsystem  108  to collect and log impressions (e.g., advertisement and/or content impressions) and associate demographic information with such logged impressions. 
     The non-partnered database proprietor subsystems  112  correspond to business entities that do not participate in sharing of demographic information. However, the techniques disclosed herein do track impressions (e.g., advertising impressions and/or content impressions) attributable to the non-partnered database proprietor subsystems  112 , and in some instances, one or more of the non-partnered database proprietor subsystems  112  also report characteristics of demographic uniqueness attributable to different impressions. Unique user IDs can be used to identify demographics using demographics information maintained by the partnered business entities (e.g., the ratings entity subsystem  106  and/or the database proprietor subsystems  108 ,  110 ). 
     The database proprietor subsystem  108  of the example of  FIG. 1  is implemented by a social network proprietor such as Facebook. However, the database proprietor subsystem  108  may instead be operated by any other type of entity such as a web services entity that serves desktop/stationary computer users and/or mobile device users. In the illustrated example, the database proprietor subsystem  108  is in a first internet domain, and the partnered database proprietor subsystems  110  and/or the non-partnered database proprietor subsystems  112  are in second, third, fourth, etc. internet domains. 
     In the illustrated example of  FIG. 1 , the tracked content and/or advertisements  102  are presented to TV and/or PC (computer) panelists  114  and online only panelists  116 . The panelists  114  and  116  are users registered on panels maintained by a ratings entity (e.g., an audience measurement company) that owns and/or operates the ratings entity subsystem  106 . In the example of  FIG. 1 , the TV and PC panelists  114  include users and/or homes that are monitored for exposures to the content and/or advertisements  102  on TVs and/or computers. The online only panelists  116  include users that are monitored for exposure (e.g., content exposure and/or advertisement exposure) via online sources when at work or home. In some example implementations, TV and/or PC panelists  114  may be home-centric users (e.g., home-makers, students, adolescents, children, etc.), while online only panelists  116  may be business-centric users that are commonly connected to work-provided Internet services via office computers or mobile devices (e.g., mobile phones, smartphones, laptops, tablet computers, etc.). 
     To collect exposure measurements (e.g., content impressions and/or advertisement impressions) generated by meters at client devices (e.g., computers, mobile phones, smartphones, laptops, tablet computers, TVs, etc.), the ratings entity subsystem  106  includes a ratings entity collector  117  and loader  118  to perform collection and loading processes. The ratings entity collector  117  and loader  118  collect and store the collected exposure measurements obtained via the panelists  114  and  116  in a ratings entity database  120 . The ratings entity subsystem  106  then processes and filters the exposure measurements based on business rules  122  and organizes the processed exposure measurements into TV&amp;PC summary tables  124 , online home (H) summary tables  126 , and online work (W) summary tables  128 . In the illustrated example, the summary tables  124 ,  126 , and  128  are sent to a GRP report generator  130 , which generates one or more GRP report(s)  131  to sell or otherwise provide to advertisers, publishers, manufacturers, content providers, and/or any other entity interested in such market research. 
     In the illustrated example of  FIG. 1 , the ratings entity subsystem  106  is provided with an impression monitor system  132  that is configured to track exposure quantities (e.g., content impressions and/or advertisement impressions) corresponding to content and/or advertisements presented by client devices (e.g., computers, mobile phones, smartphones, laptops, tablet computers, etc.) whether received from remote web servers or retrieved from local caches of the client devices. In some example implementations, the impression monitor system  132  may be implemented using the SiteCensus system owned and operated by The Nielsen Company. In the illustrated example, identities of users associated with the exposure quantities are collected using cookies (e.g., Universally Unique Identifiers (UUIDs)) tracked by the impression monitor system  132  when client devices present content and/or advertisements. Due to Internet security protocols, the impression monitor system  132  can only collect cookies set in its domain. Thus, if, for example, the impression monitor system  132  operates in the “Nielsen.com” domain, it can only collect cookies set by a Nielsen.com server. Thus, when the impression monitor system  132  receives a beacon request from a given client, the impression monitor system  132  only has access to cookies set on that client by a server in, for example, the Nielsen.com domain. To overcome this limitation, the impression monitor system  132  of the illustrated example is structured to forward beacon requests to one or more database proprietors partnered with the audience measurement entity. Those one or more partners can recognize cookies set in their domain (e.g., Facebook.com) and therefore log impressions in association with the subscribers associated with the recognized cookies. This process is explained further below. 
     In the illustrated example, the ratings entity subsystem  106  includes a ratings entity cookie collector  134  to collect cookie information (e.g., user ID information) together with content IDs and/or ad IDs associated with the cookies from the impression monitor system  132  and send the collected information to the GRP report generator  130 . Again, the cookies collected by the impression monitor system  132  are those set by server(s) operating in a domain of the audience measurement entity. In some examples, the ratings entity cookie collector  134  is configured to collect logged impressions (e.g., based on cookie information and ad or content IDs) from the impression monitor system  132  and provide the logged impressions to the GRP report generator  130 . 
     The operation of the impression monitor system  132  in connection with client devices and partner sites is described below in connection with  FIGS. 2 and 3 . In particular,  FIGS. 2 and 3  depict how the impression monitor system  132  enables collecting user identities and tracking exposure quantities for content and/or advertisements exposed to those users. The collected data can be used to determine information about, for example, the effectiveness of advertisement campaigns. 
     For purposes of example, the following example involves a social network provider, such as Facebook, as the database proprietor. In the illustrated example, the database proprietor subsystem  108  includes servers  138  to store user registration information, perform web server processes to serve web pages (possibly, but not necessarily including one or more advertisements) to subscribers of the social network, to track user activity, and to track account characteristics. During account creation, the database proprietor subsystem  108  asks users to provide demographic information such as age, gender, geographic location, graduation year, quantity of group associations, and/or any other personal or demographic information. To automatically identify users on return visits to the webpage(s) of the social network entity, the servers  138  set cookies on client devices (e.g., computers and/or mobile devices of registered users, some of which may be panelists  114  and  116  of the audience measurement entity and/or may not be panelists of the audience measurement entity). The cookies may be used to identify users to track user visits to the webpages of the social network entity, to display those web pages according to the preferences of the users, etc. The cookies set by the database proprietor subsystem  108  may also be used to collect “domain specific” user activity. As used herein, “domain specific” user activity is user Internet activity occurring within the domain(s) of a single entity. Domain specific user activity may also be referred to as “intra-domain activity.” The social network entity may collect intra-domain activity such as the number of web pages (e.g., web pages of the social network domain such as other social network member pages or other intra-domain pages) visited by each registered user and/or the types of devices such as mobile (e.g., smartphones) or stationary (e.g., desktop computers) devices used for such access. The servers  138  are also configured to track account characteristics such as the quantity of social connections (e.g., friends) maintained by each registered user, the quantity of pictures posted by each registered user, the quantity of messages sent or received by each registered user, and/or any other characteristic of user accounts. 
     The database proprietor subsystem  108  includes a database proprietor (DP) collector  139  and a DP loader  140  to collect user registration data (e.g., demographic data), intra-domain user activity data, inter-domain user activity data (as explained later) and account characteristics data. The collected information is stored in a database proprietor database  142 . The database proprietor subsystem  108  processes the collected data using business rules  144  to create DP summary tables  146 . 
     In the illustrated example, the other partnered database proprietor subsystems  110  may share with the audience measurement entity similar types of information as that shared by the database proprietor subsystem  108 . In this manner, demographic information of people that are not registered users of the social network services provider may be obtained from one or more of the other partnered database proprietor subsystems  110  if they are registered users of those web service providers (e.g., Yahoo!, Google, Experian, etc.). Examples disclosed herein advantageously use this cooperation or sharing of demographic information across website domains to increase the accuracy and/or completeness of demographic information available to the audience measurement entity. By using the shared demographic data in such a combined manner with information identifying the content and/or ads  102  to which users are exposed, examples disclosed herein produce more accurate exposure-per-demographic results to enable a determination of meaningful and consistent GRPs for online advertisements. 
     As the system  100  expands, more partnered participants (e.g., like the partnered database proprietor subsystems  110 ) may join to share further distributed demographic information and advertisement viewership information for generating GRPs. 
     To preserve user privacy, the examples disclosed herein use double encryption techniques by each participating partner or entity (e.g., the subsystems  106 ,  108 ,  110 ) so that user identities are not revealed when sharing demographic and/or viewership information between the participating partners or entities. In this manner, user privacy is not compromised by the sharing of the demographic information as the entity receiving the demographic information is unable to identify the individual associated with the received demographic information unless those individuals have already consented to allow access to their information by, for example, previously joining a panel or services of the receiving entity (e.g., the audience measurement entity). If the individual is already in the receiving party&#39;s database, the receiving party will be able to identify the individual despite the encryption. However, the individual has already agreed to be in the receiving party&#39;s database, so consent to allow access to their demographic and behavioral information has previously already been received. 
       FIG. 2  depicts an example system  200  that may be used to associate exposure measurements with user demographic information based on demographics information distributed across user account records of different database proprietors (e.g., web service providers). The example system  200  enables the ratings entity subsystem  106  of  FIG. 1  to locate a best-fit partner (e.g., the database proprietor subsystem  108  of  FIG. 1  and/or one of the other partnered database proprietor subsystems  110  of  FIG. 1 ) for each beacon request (e.g., a request from a client executing a tag associated with tagged media such as an advertisement or content that contains data identifying the media to enable an entity to log an exposure or impression). In some examples, the example system  200  uses rules and machine learning classifiers (e.g., based on an evolving set of empirical data) to determine a relatively best-suited partner that is likely to have demographics information for a user that triggered a beacon request. The rules may be applied based on a publisher level, a campaign/publisher level, or a user level. In some examples, machine learning is not employed and instead, the partners are contacted in some ordered fashion (e.g., Facebook, Myspace, then Yahoo!, etc.) until the user associated with a beacon request is identified or all partners are exhausted without an identification. 
     The ratings entity subsystem  106  receives and compiles the impression data from all available partners. The ratings entity subsystem  106  may weight the impression data based on the overall reach and demographic quality of the partner sourcing the data. For example, the ratings entity subsystem  106  may refer to historical data on the accuracy of a partner&#39;s demographic data to assign a weight to the logged data provided by that partner. 
     For rules applied at a publisher level, a set of rules and classifiers are defined that allow the ratings entity subsystem  106  to target the most appropriate partner for a particular publisher (e.g., a publisher of one or more of the advertisements or content  102  of  FIG. 1 ). For example, the ratings entity subsystem  106  could use the demographic composition of the publisher and partner web service providers to select the partner most likely to have an appropriate user base (e.g., registered users that are likely to access content for the corresponding publisher). 
     For rules applied at a campaign level, for instances in which a publisher has the ability to target an ad campaign based on user demographics, the target partner site could be defined at the publisher/campaign level. For example, if an ad campaign is targeted at males aged between the ages of 18 and 25, the ratings entity subsystem  106  could use this information to direct a request to the partner most likely to have the largest reach within that gender/age group (e.g., a database proprietor that maintains a sports website, etc.). 
     For rules applied at the user level (or cookie level), the ratings entity subsystem  106  can dynamically select a preferred partner to identify the client and log the impression based on, for example, (1) feedback received from partners (e.g., feedback indicating that panelist user IDs did not match registered users of the partner site or indicating that the partner site does not have a sufficient number of registered users), and/or (2) user behavior (e.g., user browsing behavior may indicate that certain users are unlikely to have registered accounts with particular partner sites). In the illustrated example of  FIG. 2 , rules may be used to specify when to override a user level preferred partner with a publisher (or publisher campaign) level partner target. 
     Turning in detail to  FIG. 2 , a panelist computer  202  represents a computer used by one or more of the panelists  114  and  116  of  FIG. 1 . As shown in the example of  FIG. 2 , the panelist computer  202  may exchange communications with the impression monitor system  132  of  FIG. 1 . In the illustrated example, a partner A  206  may be the database proprietor subsystem  108  of  FIG. 1  and a partner B  208  may be one of the other partnered database proprietor subsystems  110  of  FIG. 1 . A panel collection platform  210  contains the ratings entity database  120  of  FIG. 1  to collect ad and/or content exposure data (e.g., impression data or content impression data). Interim collection platforms are likely located at the partner A  206  and partner B  208  sites to store logged impressions, at least until the data is transferred to the audience measurement entity. 
     The panelist computer  202  of the illustrated example executes a web browser  212  that is directed to a host website (e.g., www.acme.com) that displays one of the advertisements and/or content  102 . The advertisement and/or content  102  is tagged with identifier information (e.g., a campaign ID, a creative type ID, a placement ID, a publisher source URL, etc.) and beacon instructions  214 . When the beacon instructions  214  are executed by the panelist computer  202 , the beacon instructions cause the panelist computer to send a beacon request to a remote server specified in the beacon instructions  214 . In the illustrated example, the specified server is a server of the audience measurement entity, namely, at the impression monitor system  132 . The beacon instructions  214  may be implemented using javascript or any other types of instructions or script executable via a web browser including, for example, Java, HTML, etc. It should be noted that tagged webpages and/or advertisements are processed the same way by panelist and non-panelist computers. In both systems, the beacon instructions are received in connection with the download of the tagged content and cause a beacon request to be sent from the client that downloaded the tagged content for the audience measurement entity. A non-panelist computer is shown at reference number  203 . Although the client  203  is not a panelist  114 ,  116 , the impression monitor system  132  may interact with the client  203  in the same manner as the impression monitor system  132  interacts with the client computer  202 , associated with one of the panelists  114 ,  116 . As shown in  FIG. 2 , the non-panelist client  203  also sends a beacon request  215  based on tagged content downloaded and presented on the non-panelist client  203 . As a result, in the following description panelist computer  202  and non-panelist computer  203  are referred to generically as a “client” computer. 
     In the illustrated example, the web browser  212  stores one or more partner cookie(s)  216  and a panelist monitor cookie  218 . Each partner cookie  216  corresponds to a respective partner (e.g., the partners A  206  and B  208 ) and can be used only by the respective partner to identify a user of the panelist computer  202 . The panelist monitor cookie  218  is a cookie set by the impression monitor system  132  and identifies the user of the panelist computer  202  to the impression monitor system  132 . Each of the partner cookies  216  is created, set, or otherwise initialized in the panelist computer  202  when a user of the computer first visits a website of a corresponding partner (e.g., one of the partners A  206  and B  208 ) and/or when a user of the computer registers with the partner (e.g., sets up a Facebook account). If the user has a registered account with the corresponding partner, the user ID (e.g., an email address or other value) of the user is mapped to the corresponding partner cookie  216  in the records of the corresponding partner. The panelist monitor cookie  218  is created when the client (e.g., a panelist computer or a non-panelist computer) registers for the panel and/or when the client processes a tagged advertisement. The panelist monitor cookie  218  of the panelist computer  202  may be set when the user registers as a panelist and is mapped to a user ID (e.g., an email address or other value) of the user in the records of the ratings entity. Although the non-panelist client computer  203  is not part of a panel, a panelist monitor cookie similar to the panelist monitor cookie  218  is created in the non-panelist client computer  203  when the non-panelist client computer  203  processes a tagged advertisement. In this manner, the impression monitor system  132  may collect impressions (e.g., ad impressions) associated with the non-panelist client computer  203  even though a user of the non-panelist client computer  203  is not registered in a panel and the ratings entity operating the impression monitor system  132  will not have demographics for the user of the non-panelist client computer  203 . 
     In some examples, the web browser  212  may also include a partner-priority-order cookie  220  that is set, adjusted, and/or controlled by the impression monitor system  132  and includes a priority listing of the partners  206  and  208  (and/or other database proprietors) indicative of an order in which beacon requests should be sent to the partners  206 ,  208  and/or other database proprietors. For example, the impression monitor system  132  may specify that the client computer  202 ,  203  should first send a beacon request based on execution of the beacon instructions  214  to partner A  206  and then to partner B  208  if partner A  206  indicates that the user of the client computer  202 ,  203  is not a registered user of partner A  206 . In this manner, the client computer  202 ,  203  can use the beacon instructions  214  in combination with the priority listing of the partner-priority-order cookie  220  to send an initial beacon request to an initial partner and/or other initial database proprietor and one or more redirected beacon requests to one or more secondary partners and/or other database proprietors until one of the partners  206  and  208  and/or other database proprietors confirms that the user of the panelist computer  202  is a registered user of the partner&#39;s or other database proprietor&#39;s services and is able to log an impression (e.g., an ad impression, a content impression, etc.) and provide demographic information for that user (e.g., demographic information stored in the database proprietor database  142  of  FIG. 1 ), or until all partners have been tried without a successful match. In other examples, the partner-priority-order cookie  220  may be omitted and the beacon instructions  214  may be configured to cause the client computer  202 ,  203  to unconditionally send beacon requests to all available partners and/or other database proprietors so that all of the partners and/or other database proprietors have an opportunity to log an impression. In yet other examples, the beacon instructions  214  may be configured to cause the client computer  202 ,  203  to receive instructions from the impression monitor system  132  on an order in which to send redirected beacon requests to one or more partners and/or other database proprietors. 
     To monitor browsing behavior and track activity of the partner cookie(s)  216 , the panelist computer  202  is provided with a web client meter  222 . In addition, the panelist computer  202  is provided with an HTTP request log  224  in which the web client meter  222  may store or log HTTP requests in association with a meter ID of the web client meter  222 , user IDs originating from the panelist computer  202 , beacon request timestamps (e.g., timestamps indicating when the panelist computer  202  sent beacon requests such as the beacon requests  304  and  308  of  FIG. 3 ), uniform resource locators (URLs) of websites that displayed advertisements, and ad campaign IDs. In the illustrated example, the web client meter  222  stores user IDs of the partner cookie(s)  216  and the panelist monitor cookie  218  in association with each logged HTTP request in the HTTP requests log  224 . In some examples, the HTTP requests log  224  can additionally or alternatively store other types of requests such as file transfer protocol (FTP) requests and/or any other internet protocol requests. The web client meter  222  of the illustrated example can communicate such web browsing behavior or activity data in association with respective user IDs from the HTTP requests log  224  to the panel collection platform  210 . In some examples, the web client meter  222  may also be advantageously used to log impressions for untagged content or advertisements. Unlike tagged advertisements and/or tagged content that include the beacon instructions  214  causing a beacon request to be sent to the impression monitor system  132  (and/or one or more of the partners  206 ,  208  and/or other database proprietors) identifying the exposure or impression to the tagged content to be sent to the audience measurement entity for logging, untagged advertisements and/or advertisements do not have such beacon instructions  214  to create an opportunity for the impression monitor system  132  to log an impression. In such instances, HTTP requests logged by the web client meter  222  can be used to identify any untagged content or advertisements that were rendered by the web browser  212  on the panelist computer  202 . 
     In the illustrated example, the impression monitor system  132  is provided with a user ID comparator  228 , a rules/machine learning (ML) engine  230 , an HTTP server  232 , and a publisher/campaign/user target database  234 . The user ID comparator  228  of the illustrated example is provided to identify beacon requests from users that are panelists  114 ,  116 . In the illustrated example, the HTTP server  232  is a communication interface via which the impression monitor system  132  exchanges information (e.g., beacon requests, beacon responses, acknowledgements, failure status messages, etc.) with the client computer  202 ,  203 . The rules/ML engine  230  and the publisher/campaign/user target database  234  of the illustrated example enable the impression monitor system  132  to target the ‘best fit’ partner (e.g., one of the partners  206  or  208 ) for each impression request (or beacon request) received from the client computer  202 ,  203 . The ‘best fit’ partner is the partner most likely to have demographic data for the user(s) of the client computer  202 ,  203  sending the impression request. The rules/ML engine  230  is a set of rules and machine learning classifiers generated based on evolving empirical data stored in the publisher/campaign/user target database  234 . In the illustrated example, rules can be applied at the publisher level, publisher/campaign level, or user level. In addition, partners may be weighted based on their overall reach and demographic quality. 
     To target partners (e.g., the partners  206  and  208 ) at the publisher level of ad campaigns, the rules/ML engine  230  contains rules and classifiers that allow the impression monitor system  132  to target the ‘best fit’ partner for a particular publisher of ad campaign(s). For example, the impression monitoring system  132  could use an indication of target demographic composition(s) of publisher(s) and partner(s) (e.g., as stored in the publisher/campaign/user target database  234 ) to select a partner (e.g., one of the partners  206 ,  208 ) that is most likely to have demographic information for a user of the client computer  202 ,  203  requesting the impression. 
     To target partners (e.g., the partners  206  and  208 ) at the campaign level (e.g., a publisher has the ability to target ad campaigns based on user demographics), the rules/ML engine  230  of the illustrated example are used to specify target partners at the publisher/campaign level. For example, if the publisher/campaign/user target database  234  stores information indicating that a particular ad campaign is targeted at males aged 18 to 25, the rules/ML engine  230  uses this information to indicate a beacon request redirect to a partner most likely to have the largest reach within this gender/age group. 
     To target partners (e.g., the partners  206  and  208 ) at the cookie level, the impression monitor system  132  updates target partner sites based on feedback received from the partners. Such feedback could indicate user IDs that did not correspond or that did correspond to registered users of the partner(s). In some examples, the impression monitor system  132  could also update target partner sites based on user behavior. For example, such user behavior could be derived from analyzing cookie clickstream data corresponding to browsing activities associated with panelist monitor cookies (e.g., the panelist monitor cookie  218 ). In the illustrated example, the impression monitor system  132  uses such cookie clickstream data to determine age/gender bias for particular partners by determining ages and genders of which the browsing behavior is more indicative. In this manner, the impression monitor system  132  of the illustrated example can update a target or preferred partner for a particular user or client computer  202 ,  203 . In some examples, the rules/ML engine  230  specify when to override user-level preferred target partners with publisher or publisher/campaign level preferred target partners. For example such a rule may specify an override of user-level preferred target partners when the user-level preferred target partner sends a number of indications that it does not have a registered user corresponding to the client computer  202 ,  203  (e.g., a different user on the client computer  202 ,  203  begins using a different browser having a different user ID in its partner cookie  216 ). 
     In the illustrated example, the impression monitor system  132  logs impressions (e.g., ad impressions, content impressions, etc.) in an impressions per unique users table  235  based on beacon requests (e.g., the beacon request  304  of  FIG. 3 ) received from client computers (e.g., the client computer  202 ,  203 ). In the illustrated example, the impressions per unique users table  235  stores unique user IDs obtained from cookies (e.g., the panelist monitor cookie  218 ) in association with total impressions per day and campaign IDs. In this manner, for each campaign ID, the impression monitor system  132  logs the total impressions per day that are attributable to a particular user or client computer  202 ,  203 . 
     Each of the partners  206  and  208  of the illustrated example employs an HTTP server  236  and  240  and a user ID comparator  238  and  242 . In the illustrated example, the HTTP servers  236  and  240  are communication interfaces via which their respective partners  206  and  208  exchange information (e.g., beacon requests, beacon responses, acknowledgements, failure status messages, etc.) with the client computer  202 ,  203 . The user ID comparators  238  and  242  are configured to compare user cookies received from a client  202 ,  203  against the cookie in their records to identify the client  202 ,  203 , if possible. In this manner, the user ID comparators  238  and  242  can be used to determine whether users of the panelist computer  202  have registered accounts with the partners  206  and  208 . If so, the partners  206  and  208  can log impressions attributed to those users and associate those impressions with the demographics of the identified user (e.g., demographics stored in the database proprietor database  142  of  FIG. 1 ). 
     In the illustrated example, the panel collection platform  210  is used to identify registered users of the partners  206 ,  208  that are also panelists  114 ,  116 . The panel collection platform  210  can then use this information to cross-reference demographic information stored by the ratings entity subsystem  106  for the panelists  114 ,  116  with demographic information stored by the partners  206  and  208  for their registered users. The ratings entity subsystem  106  can use such cross-referencing to determine the accuracy of the demographic information collected by the partners  206  and  208  based on the demographic information of the panelists  114  and  116  collected by the ratings entity subsystem  106 . 
     In some examples, the example collector  117  of the panel collection platform  210  collects web-browsing activity information from the panelist computer  202 . In such examples, the example collector  117  requests logged data from the HTTP requests log  224  of the panelist computer  202  and logged data collected by other panelist computers (not shown). In addition, the collector  117  collects panelist user IDs from the impression monitor system  132  that the impression monitor system  132  tracks as having set in panelist computers. Also, the collector  117  collects partner user IDs from one or more partners (e.g., the partners  206  and  208 ) that the partners track as having been set in panelist and non-panelist computers. In some examples, to abide by privacy agreements of the partners  206 ,  208 , the collector  117  and/or the database proprietors  206 ,  208  can use a hashing technique (e.g., a double-hashing technique) to hash the database proprietor cookie IDs. 
     In some examples, the loader  118  of the panel collection platform  210  analyzes and sorts the received panelist user IDs and the partner user IDs. In the illustrated example, the loader  118  analyzes received logged data from panelist computers (e.g., from the HTTP requests log  224  of the panelist computer  202 ) to identify panelist user IDs (e.g., the panelist monitor cookie  218 ) associated with partner user IDs (e.g., the partner cookie(s)  216 ). In this manner, the loader  118  can identify which panelists (e.g., ones of the panelists  114  and  116 ) are also registered users of one or more of the partners  206  and  208  (e.g., the database proprietor subsystem  108  of  FIG. 1  having demographic information of registered users stored in the database proprietor database  142 ). In some examples, the panel collection platform  210  operates to verify the accuracy of impressions collected by the impression monitor system  132 . In such some examples, the loader  118  filters the logged HTTP beacon requests from the HTTP requests log  224  that correlate with impressions of panelists logged by the impression monitor system  132  and identifies HTTP beacon requests logged at the HTTP requests log  224  that do not have corresponding impressions logged by the impression monitor system  132 . In this manner, the panel collection platform  210  can provide indications of inaccurate impression logging by the impression monitor system  132  and/or provide impressions logged by the web client meter  222  to fill-in impression data for panelists  114 ,  116  missed by the impression monitor system  132 . 
     In the illustrated example, the loader  118  stores overlapping users in an impressions-based panel demographics table  250 . In the illustrated example, overlapping users are users that are panelist members  114 ,  116  and registered users of partner A  206  (noted as users P(A)) and/or registered users of partner B  208  (noted as users P(B)). (Although only two partners (A and B) are shown, this is for simplicity of illustration, any number of partners may be represented in the table  250 . The impressions-based panel demographics table  250  of the illustrated example is shown storing meter IDs (e.g., of the web client meter  222  and web client meters of other computers), user IDs (e.g., an alphanumeric identifier such as a user name, email address, etc. corresponding to the panelist monitor cookie  218  and panelist monitor cookies of other panelist computers), beacon request timestamps (e.g., timestamps indicating when the panelist computer  202  and/or other panelist computers sent beacon requests such as the beacon requests  304  and  308  of  FIG. 3 ), uniform resource locators (URLs) of websites visited (e.g., websites that displayed advertisements), and ad campaign IDs. In addition, the loader  118  of the illustrated example stores partner user IDs that do not overlap with panelist user IDs in a partner A (P(A)) cookie table  252  and a partner B (P(B)) cookie table  254 . 
     Example processes performed by the example system  200  are described below in connection with the communications flow diagram of  FIG. 3  and the flow diagrams of  FIGS. 10, 11, and 12 . 
     While an example manner of implementing the ratings entity subsystem  106  is illustrated in  FIGS. 1 and 2 , one or more of the elements, processes and/or devices illustrated in  FIGS. 1 and 2  may be combined, divided, re-arranged, omitted, eliminated and/or implemented in any other way. Further, the example impression monitor system  132 , the example rules/ML engine  230 , the example HTTP server communication interface  232 , the example publisher/campaign/user target database  232 , the example GRP report generator  130 , the example panel collection platform  210 , the example collector  117 , the example loader  118 , the example ratings entity database  120  and/or, more generally, the example ratings entity subsystem  106  of  FIGS. 1 and 2  may be implemented by hardware, software, firmware and/or any combination of hardware, software and/or firmware. Thus, for example, any of the example impression monitor system  132 , the example rules/ML engine  230 , the example HTTP server communication interface  232 , the example publisher/campaign/user target database  232 , the example GRP report generator  130 , the example panel collection platform  210 , the example collector  117 , the example loader  118 , the example ratings entity database  120  and/or, more generally, the example ratings entity subsystem  106  could be implemented by one or more analog or digital circuit(s), logic circuits, programmable processor(s), application specific integrated circuit(s) (ASIC(s)), programmable logic device(s) (PLD(s)) and/or field programmable logic device(s) (FPLD(s)). When reading any of the apparatus or system claims of this patent to cover a purely software and/or firmware implementation, at least one of the example impression monitor system  132 , the example rules/ML engine  230 , the example HTTP server communication interface  232 , the example publisher/campaign/user target database  232 , the example GRP report generator  130 , the example panel collection platform  210 , the example collector  117 , the example loader  118 , and/or the example ratings entity database  120  is/are hereby expressly defined to include a tangible computer readable storage device or storage disk such as a memory, a digital versatile disk (DVD), a compact disk (CD), a Blu-ray disk, etc. storing the software and/or firmware. Further still, the example ratings entity subsystem  106  of  FIGS. 1 and 2  may include one or more elements, processes and/or devices in addition to, or instead of, those illustrated in  FIGS. 1 and 2 , and/or may include more than one of any or all of the illustrated elements, processes and devices. 
     Turning to  FIG. 3 , an example communication flow diagram shows an example manner in which the example system  200  of  FIG. 2  logs impressions by clients (e.g., clients  202 ,  203 ). The example chain of events shown in  FIG. 3  occurs when a client  202 ,  203  accesses a tagged advertisement or tagged content. Thus, the events of  FIG. 3  begin when a client sends an HTTP request to a server for content and/or an advertisement, which, in this example, is tagged to forward an exposure request to the ratings entity. In the illustrated example of  FIG. 3 , the web browser of the client  202 ,  203  receives the requested content or advertisement (e.g., the content or advertisement  102 ) from a publisher (e.g., ad publisher  302 ). It is to be understood that the client  202 ,  203  often requests a webpage containing content of interest (e.g., www.weather.com) and the requested webpage contains links to ads that are downloaded and rendered within the webpage. The ads may come from different servers than the originally requested content. Thus, the requested content may contain instructions that cause the client  202 ,  203  to request the ads (e.g., from the ad publisher  302 ) as part of the process of rendering the webpage originally requested by the client. The webpage, the ad or both may be tagged. In the illustrated example, the uniform resource locator (URL) of the ad publisher is illustratively named http://my.advertiser.com. 
     For purposes of the following illustration, it is assumed that the advertisement  102  is tagged with the beacon instructions  214  ( FIG. 2 ). Initially, the beacon instructions  214  cause the web browser of the client  202  or  203  to send a beacon request  304  to the impression monitor system  132  when the tagged ad is accessed. In the illustrated example, the web browser sends the beacon request  304  using an HTTP request addressed to the URL of the impression monitor system  132  at, for example, a first internet domain. The beacon request  304  includes one or more of a campaign ID, a creative type ID, and/or a placement ID associated with the advertisement  102 . In addition, the beacon request  304  includes a document referrer (e.g., www.acme.com), a timestamp of the impression, and a publisher site ID (e.g., the URL http://my.advertiser.com of the ad publisher  302 ). In addition, if the web browser of the client  202  or  203  contains the panelist monitor cookie  218 , the beacon request  304  will include the panelist monitor cookie  218 . In other example implementations, the cookie  218  may not be passed until the client  202  or  203  receives a request sent by a server of the impression monitor system  132  in response to, for example, the impression monitor system  132  receiving the beacon request  304 . 
     In response to receiving the beacon request  304 , the impression monitor system  132  logs an impression by recording the ad identification information (and any other relevant identification information) contained in the beacon request  304 . In the illustrated example, the impression monitor system  132  logs the impression regardless of whether the beacon request  304  indicated a user ID (e.g., based on the panelist monitor cookie  218 ) that matched a user ID of a panelist member (e.g., one of the panelists  114  and  116  of  FIG. 1 ). However, if the user ID (e.g., the panelist monitor cookie  218 ) matches a user ID of a panelist member (e.g., one of the panelists  114  and  116  of  FIG. 1 ) set by and, thus, stored in the record of the ratings entity subsystem  106 , the logged impression will correspond to a panelist of the impression monitor system  132 . If the user ID does not correspond to a panelist of the impression monitor system  132 , the impression monitor system  132  will still benefit from logging an impression even though it will not have a user ID record (and, thus, corresponding demographics) for the impression reflected in the beacon request  304 . 
     In the illustrated example of  FIG. 3 , to compare or supplement panelist demographics (e.g., for accuracy or completeness) of the impression monitor system  132  with demographics at partner sites and/or to enable a partner site to attempt to identify the client and/or log the impression, the impression monitor system  132  returns a beacon response message  306  (e.g., a first beacon response) to the web browser of the client  202 ,  203  including an HTTP  302  redirect message and a URL of a participating partner at, for example, a second internet domain. In the illustrated example, the HTTP  302  redirect message instructs the web browser of the client  202 ,  203  to send a second beacon request  308  to the particular partner (e.g., one of the partners A  206  or B  208 ). In other examples, instead of using an HTTP  302  redirect message, redirects may instead be implemented using, for example, an iframe source instructions (e.g., &lt;iframe src=“ ”&gt;) or any other instruction that can instruct a web browser to send a subsequent beacon request (e.g., the second beacon request  308 ) to a partner. In the illustrated example, the impression monitor system  132  determines the partner specified in the beacon response  306  using its rules/ML engine  230  ( FIG. 2 ) based on, for example, empirical data indicative of which partner should be preferred as being most likely to have demographic data for the user ID. In other examples, the same partner is always identified in the first redirect message and that partner always redirects the client  202 ,  203  to the same second partner when the first partner does not log the impression. In other words, a set hierarchy of partners is defined and followed such that the partners are “daisy chained” together in the same predetermined order rather than them trying to guess a most likely database proprietor to identify an unknown client  203 . 
     Prior to sending the beacon response  306  to the web browser of the client  202 ,  203 , the impression monitor system  132  of the illustrated example replaces a site ID (e.g., a URL) of the ad publisher  302  with a modified site ID (e.g., a substitute site ID) which is discernable only by the impression monitor system  132  as corresponding to the ad publisher  302 . In some example implementations, the impression monitor system  132  may also replace the host website ID (e.g., www.acme.com) with another modified site ID (e.g., a substitute site ID) which is discernable only by the impression monitor system  132  as corresponding to the host website. In this way, the source(s) of the ad and/or the host content are masked from the partners. In the illustrated example, the impression monitor system  132  maintains a publisher ID mapping table  310  that maps original site IDs of ad publishers with modified (or substitute) site IDs created by the impression monitor system  132  to obfuscate or hide ad publisher identifiers from partner sites. In some examples, the impression monitor system  132  also stores the host website ID in association with a modified host website ID in a mapping table. In addition, the impression monitor system  132  encrypts all of the information received in the beacon request  304  and the modified site ID to prevent any intercepting parties from decoding the information. The impression monitor system  132  of the illustrated example sends the encrypted information in the beacon response  306  to the web browser  212 . In the illustrated example, the impression monitor system  132  uses an encryption that can be decrypted by the selected partner site specified in the HTTP  302  redirect. 
     In some examples, the impression monitor system  132  also sends a URL scrape instruction  320  to the client computer  202 ,  302 . In such examples, the URL scrape instruction  320  causes the client computer  202 ,  203  to “scrape” the URL of the webpage or website associated with the tagged advertisement  102 . For example, the client computer  202 ,  203  may perform scraping of web page URLs by reading text rendered or displayed at a URL address bar of the web browser  212 . The client computer  202 ,  203  then sends a scraped URL  322  to the impression monitor system  132 . In the illustrated example, the scraped URL  322  indicates the host website (e.g., http://www.acme.com) that was visited by a user of the client computer  202 ,  203  and in which the tagged advertisement  102  was displayed. In the illustrated example, the tagged advertisement  102  is displayed via an ad iFrame having a URL ‘my.advertiser.com,’ which corresponds to an ad network (e.g., the publisher  302 ) that serves the tagged advertisement  102  on one or more host websites. However, in the illustrated example, the host website indicated in the scraped URL  322  is ‘www.acme.com,’ which corresponds to a website visited by a user of the client computer  202 ,  203 . 
     URL scraping is particularly useful under circumstances in which the publisher is an ad network from which an advertiser bought advertisement space/time. In such instances, the ad network dynamically selects from subsets of host websites (e.g., www.caranddriver.com, www.espn.com, www.allrecipes.com, etc.) visited by users on which to display ads via ad iFrames. However, the ad network cannot foretell definitively the host websites on which the ad will be displayed at any particular time. In addition, the URL of an ad iFrame in which the tagged advertisement  102  is being rendered may not be useful to identify the topic of a host website (e.g., www.acme.com in the example of  FIG. 3 ) rendered by the web browser  212 . As such, the impression monitor system  132  may not know the host website in which the ad iFrame is displaying the tagged advertisement  102 . 
     The URLs of host websites (e.g., www.caranddriver.com, www.espn.com, www.allrecipes.com, etc.) can be useful to determine topical interests (e.g., automobiles, sports, cooking, etc.) of user(s) of the client computer  202 ,  203 . In some examples, audience measurement entities can use host website URLs to correlate with user/panelist demographics and interpolate logged impressions to larger populations based on demographics and topical interests of the larger populations and based on the demographics and topical interests of users/panelists for which impressions were logged. Thus, in the illustrated example, when the impression monitor system  132  does not receive a host website URL or cannot otherwise identify a host website URL based on the beacon request  304 , the impression monitor system  132  sends the URL scrape instruction  320  to the client computer  202 ,  203  to receive the scraped URL  322 . In the illustrated example, if the impression monitor system  132  can identify a host website URL based on the beacon request  304 , the impression monitor system  132  does not send the URL scrape instruction  320  to the client computer  202 ,  203 , thereby, conserving network and computer bandwidth and resources. 
     In response to receiving the beacon response  306 , the web browser of the client  202 ,  203  sends the beacon request  308  to the specified partner site, which is the partner A  206  (e.g., a second internet domain) in the illustrated example. The beacon request  308  includes the encrypted parameters from the beacon response  306 . The partner A  206  (e.g., Facebook) decrypts the encrypted parameters and determines whether the client matches a registered user of services offered by the partner A  206 . This determination involves requesting the client  202 ,  203  to pass any cookie (e.g., one of the partner cookies  216  of  FIG. 2 ) it stores that had been set by partner A  206  and attempting to match the received cookie against the cookies stored in the records of partner A  206 . If a match is found, partner A  206  has positively identified a client  202 ,  203 . Accordingly, the partner A  206  site logs an impression in association with the demographics information of the identified client. This log (which includes the undetectable source identifier) is subsequently provided to the ratings entity for processing into GRPs as discussed below. In the event partner A  206  is unable to identify the client  202 ,  203  in its records (e.g., no matching cookie), the partner A  206  does not log an impression. 
     In some example implementations, if the user ID does not match a registered user of the partner A  206 , the partner A  206  may return a beacon response  312  (e.g., a second beacon response) including a failure or non-match status or may not respond at all, thereby terminating the process of  FIG. 3 . However, in the illustrated example, if partner A  206  cannot identify the client  202 ,  203 , partner A  206  returns a second HTTP  302  redirect message in the beacon response  312  (e.g., the second beacon response) to the client  202 ,  203 . For example, if the partner A site  206  has logic (e.g., similar to the rules/ml engine  230  of  FIG. 2 ) to specify another partner (e.g., partner B  208  or any other partner) which may likely have demographics for the user ID, then the beacon response  312  may include an HTTP  302  redirect (or any other suitable instruction to cause a redirected communication) along with the URL of the other partner (e.g., at a third internet domain). Alternatively, in the daisy chain approach discussed above, the partner A site  206  may always redirect to the same next partner or database proprietor (e.g., partner B  208  at, for example, a third internet domain or a non-partnered database proprietor subsystem  110  of  FIG. 1  at a third internet domain) whenever it cannot identify the client  202 ,  203 . When redirecting, the partner A site  206  of the illustrated example encrypts the ID, timestamp, referrer, etc. parameters using an encryption that can be decoded by the next specified partner. 
     As a further alternative, if the partner A site  206  does not have logic to select a next best suited partner likely to have demographics for the user ID and is not effectively daisy chained to a next partner by storing instructions that redirect to a partner entity, the beacon response  312  can redirect the client  202 ,  203  to the impression monitor system  132  with a failure or non-match status. In this manner, the impression monitor system  132  can use its rules/ML engine  230  to select a next-best suited partner to which the web browser of the client  202 ,  203  should send a beacon request (or, if no such logic is provided, simply select the next partner in a hierarchical (e.g., fixed) list). In the illustrated example, the impression monitor system  132  selects the partner B site  208 , and the web browser of the client  202 ,  203  sends a beacon request to the partner B site  208  with parameters encrypted in a manner that can be decrypted by the partner B site  208 . The partner B site  208  then attempts to identify the client  202 ,  203  based on its own internal database. If a cookie obtained from the client  202 ,  203  matches a cookie in the records of partner B  208 , partner B  208  has positively identified the client  202 ,  203  and logs the impression in association with the demographics of the client  202 ,  203  for later provision to the impression monitor system  132 . In the event that partner B  208  cannot identify the client  202 ,  203 , the same process of failure notification or further HTTP  302  redirects may be used by the partner B  208  to provide a next other partner site an opportunity to identify the client and so on in a similar manner until a partner site identifies the client  202 ,  203  and logs the impression, until all partner sites have been exhausted without the client being identified, or until a predetermined number of partner sites failed to identify the client  202 ,  203 . 
     Using the process illustrated in  FIG. 3 , impressions (e.g., ad impressions, content impressions, etc.) can be mapped to corresponding demographics even when the impressions are not triggered by panel members associated with the audience measurement entity (e.g., ratings entity subsystem  106  of  FIG. 1 ). That is, during an impression collection or merging process, the panel collection platform  210  of the ratings entity can collect distributed impressions logged by (1) the impression monitor system  132  and (2) any participating partners (e.g., partners  206 ,  208 ). As a result, the collected data covers a larger population with richer demographics information than has heretofore been possible. Consequently, generating accurate, consistent, and meaningful online GRPs is possible by pooling the resources of the distributed databases as described above. The example structures of  FIGS. 2 and 3  generate online GRPs based on a large number of combined demographic databases distributed among unrelated parties (e.g., Nielsen and Facebook). The end result appears as if users attributable to the logged impressions were part of a large virtual panel formed of registered users of the audience measurement entity because the selection of the participating partner sites can be tracked as if they were members of the audience measurement entities panels  114 ,  116 . This is accomplished without violating the cookie privacy protocols of the Internet. 
     Periodically or aperiodically, the impression data collected by the partners (e.g., partners  206 ,  208 ) is provided to the ratings entity via a panel collection platform  210 . As discussed above, some user IDs may not match panel members of the impression monitor system  132 , but may match registered users of one or more partner sites. During a data collecting and merging process to combine demographic and impression data from the ratings entity subsystem  106  and the partner subsystem(s)  108  and  110  of  FIG. 1 , user IDs of some impressions logged by one or more partners may match user IDs of impressions logged by the impression monitor system  132 , while others (most likely many others) will not match. In some example implementations, the ratings entity subsystem  106  may use the demographics-based impressions from matching user ID logs provided by partner sites to assess and/or improve the accuracy of its own demographic data, if necessary. For the demographics-based impressions associated with non-matching user ID logs, the ratings entity subsystem  106  may use the impressions (e.g., advertisement impressions, content impressions, etc.) to derive demographics-based online GRPs even though such impressions are not associated with panelists of the ratings entity subsystem  106 . 
     As briefly mentioned above, examples disclosed herein may be configured to preserve user privacy when sharing demographic information (e.g., account records or registration information) between different entities (e.g., between the ratings entity subsystem  106  and the database proprietor subsystem  108 ). In some example implementations, a double encryption technique may be used based on respective secret keys for each participating partner or entity (e.g., the subsystems  106 ,  108 ,  110 ). For example, the ratings entity subsystem  106  can encrypt its user IDs (e.g., email addresses) using its secret key and the database proprietor subsystem  108  can encrypt its user IDs using its secret key. For each user ID, the respective demographics information is then associated with the encrypted version of the user ID. Each entity then exchanges their demographics lists with encrypted user IDs. Because neither entity knows the other&#39;s secret key, they cannot decode the user IDs, and thus, the user IDs remain private. Each entity then proceeds to perform a second encryption of each encrypted user ID using their respective keys. Each twice-encrypted (or double encrypted) user ID (UID) will be in the form of E1(E2(UID)) and E2(E1(UID)), where E1 represents the encryption using the secret key of the ratings entity subsystem  106  and E2 represents the encryption using the secret key of the database proprietor subsystem  108 . Under the rule of commutative encryption, the encrypted user IDs can be compared on the basis that E1(E2(UID))=E2(E1(UID)). Thus, the encryption of user IDs present in both databases will match after the double encryption is completed. In this manner, matches between user records of the panelists and user records of the database proprietor (e.g., identifiers of registered social network users) can be compared without the partner entities needing to reveal user IDs to one another. 
     The ratings entity subsystem  106  performs a daily impressions and UUID (cookies) totalization based on impressions and cookie data collected by the impression monitor system  132  of  FIG. 1  and the impressions logged by the partner sites. In the illustrated example, the ratings entity subsystem  106  may perform the daily impressions and UUID (cookies) totalization based on cookie information collected by the ratings entity cookie collector  134  of  FIG. 1  and the logs provided to the panel collection platform  210  by the partner sites.  FIG. 4  depicts an example ratings entity impressions table  400  showing quantities of impressions to monitored users. Similar tables could be compiled for one or more of advertisement impressions, content impressions, or other impressions. In the illustrated example, the ratings entity impressions table  400  is generated by the ratings entity subsystem  106  for an advertisement campaign (e.g., one or more of the advertisements  102  of  FIG. 1 ) to determine frequencies of impressions per day for each user. 
     To track frequencies of impressions per unique user per day, the ratings entity impressions table  400  is provided with a frequency column  402 . A frequency of 1 indicates one exposure per day of an ad in an ad campaign to a unique user, while a frequency of 4 indicates four exposures per day of one or more ads in the same ad campaign to a unique user. To track the quantity of unique users to which impressions are attributable, the ratings impressions table  400  is provided with a UUIDs column  404 . A value of 100,000 in the UUIDs column  404  is indicative of 100,000 unique users. Thus, the first entry of the ratings entity impressions table  400  indicates that 100,000 unique users (i.e., UUIDs=100,000) were exposed once (i.e., frequency=1) in a single day to a particular one of the advertisements  102 . 
     To track impressions based on exposure frequency and UUIDs, the ratings entity impressions table  400  is provided with an impressions column  406 . Each impression count stored in the impressions column  406  is determined by multiplying a corresponding frequency value stored in the frequency column  402  with a corresponding UUID value stored in the UUID column  404 . For example, in the second entry of the ratings entity impressions table  400 , the frequency value of two is multiplied by 200,000 unique users to determine that 400,000 impressions are attributable to a particular one of the advertisements  102 . 
     Turning to  FIG. 5 , in the illustrated example, each of the partnered database proprietor subsystems  108 ,  110  of the partners  206 ,  208  generates and reports a database proprietor ad campaign-level age/gender and impression composition table  500  to the GRP report generator  130  of the ratings entity subsystem  106  on a daily basis. Similar tables can be generated for content and/or other media. Additionally or alternatively, media in addition to advertisements may be added to the table  500 . In the illustrated example, the partners  206 ,  208  tabulate the impression distribution by age and gender composition as shown in  FIG. 5 . For example, referring to  FIG. 1 , the database proprietor database  142  of the partnered database proprietor subsystem  108  stores logged impressions and corresponding demographic information of registered users of the partner A  206 , and the database proprietor subsystem  108  of the illustrated example processes the impressions and corresponding demographic information using the rules  144  to generate the DP summary tables  146  including the database proprietor ad campaign-level age/gender and impression composition table  500 . 
     The age/gender and impression composition table  500  is provided with an age/gender column  502 , an impressions column  504 , a frequency column  506 , and an impression composition column  508 . The age/gender column  502  of the illustrated example indicates the different age/gender demographic groups. The impressions column  504  of the illustrated example stores values indicative of the total impressions for a particular one of the advertisements  102  ( FIG. 1 ) for corresponding age/gender demographic groups. The frequency column  506  of the illustrated example stores values indicative of the frequency of exposure per user for the one of the advertisements  102  that contributed to the impressions in the impressions column  504 . The impressions composition column  508  of the illustrated example stores the percentage of impressions for each of the age/gender demographic groups. 
     In some examples, the database proprietor subsystems  108 ,  110  may perform demographic accuracy analyses and adjustment processes on its demographic information before tabulating final results of impression-based demographic information in the database proprietor campaign-level age/gender and impression composition table. This can be done to address a problem facing online audience measurement processes in that the manner in which registered users represent themselves to online data proprietors (e.g., the partners  206  and  208 ) is not necessarily veridical (e.g., truthful and/or accurate). In some instances, example approaches to online measurement that leverage account registrations at such online database proprietors to determine demographic attributes of an audience may lead to inaccurate demographic-exposure results if they rely on self-reporting of personal/demographic information by the registered users during account registration at the database proprietor site. There may be numerous reasons for why users report erroneous or inaccurate demographic information when registering for database proprietor services. The self-reporting registration processes used to collect the demographic information at the database proprietor sites (e.g., social media sites) does not facilitate determining the veracity of the self-reported demographic information. To analyze and adjust inaccurate demographic information, the ratings entity subsystem  106  and the database proprietor subsystems  108 ,  110  may use examples disclosed in U.S. patent application Ser. No. 13/209,292, filed on Aug. 12, 2011, and titled “Methods and Apparatus to Analyze and Adjust Demographic Information,” which is hereby incorporated herein by reference in its entirety. 
     Turning to  FIG. 6 , in the illustrated example, the ratings entity subsystem  106  generates a panelist ad campaign-level age/gender and impression composition table  600  on a daily basis. Similar tables can be generated for content and/or other media. Additionally or alternatively, media in addition to advertisements may be added to the table  600 . The example ratings entity subsystem  106  tabulates the impression distribution by age and gender composition as shown in  FIG. 6  in the same manner as described above in connection with  FIG. 5 . As shown in  FIG. 6 , the panelist ad campaign-level age/gender and impression composition table  600  also includes an age/gender column  602 , an impressions column  604 , a frequency column  606 , and an impression composition column  608 . In the illustrated example of  FIG. 6 , the impressions are calculated based on the PC and TV panelists  114  and online panelists  116 . 
     After creating the campaign-level age/gender and impression composition tables  500  and  600  of  FIGS. 5 and 6 , the ratings entity subsystem  106  creates a combined campaign-level age/gender and impression composition table  700  shown in  FIG. 7 . In particular, the ratings entity subsystem  106  combines the impression composition percentages from the impression composition columns  508  and  608  of  FIGS. 5 and 6  to compare the age/gender impression distribution differences between the ratings entity panelists and the social network users. 
     As shown in  FIG. 7 , the combined campaign-level age/gender and impression composition table  700  includes an error weighted column  702 , which stores mean squared errors (MSEs) indicative of differences between the impression compositions of the ratings entity panelists and the users of the database proprietor (e.g., social network users). Weighted MSEs can be determined using Equation 3 below.
 
Weighted MSE=(α*IC (RE) +(1−α)IC (DP) )  Equation 3
 
     In Equation 3 above, a weighting variable (α) represents the ratio of MSE(SN)/MSE(RE) or some other function that weights the compositions inversely proportional to their MSE. As shown in Equation 3, the weighting variable (α) is multiplied by the impression composition of the ratings entity (IC(RE)) to generate a ratings entity weighted impression composition (α*IC(RE)). The impression composition of the database proprietor (e.g., a social network) (IC(DP)) is then multiplied by a difference between one and the weighting variable (α) to determine a database proprietor weighted impression composition ((1−α) IC(DP)). 
     In the illustrated example, the ratings entity subsystem  106  can smooth or correct the differences between the impression compositions by weighting the distribution of MSE. The MSE values account for sample size variations or bounces in data caused by small sample sizes. 
     Turning to  FIG. 8 , the ratings entity subsystem  106  determines reach and error-corrected impression compositions in an age/gender impressions distribution table  800 . The age/gender impressions distribution table  800  includes an age/gender column  802 , an impressions column  804 , a frequency column  806 , a reach column  808 , and an impressions composition column  810 . The impressions column  804  stores error-weighted impressions values corresponding to impressions tracked by the ratings entity subsystem  106  (e.g., the impression monitor system  132  and/or the panel collection platform  210  based on impressions logged by the web client meter  222 ). In particular, the values in the impressions column  804  are derived by multiplying weighted MSE values from the error weighted column  702  of  FIG. 7  with corresponding impressions values from the impressions column  604  of  FIG. 6 . 
     The frequency column  806  stores frequencies of impressions as tracked by the database proprietor subsystem  108 . The frequencies of impressions are imported into the frequency column  806  from the frequency column  506  of the database proprietor campaign-level age/gender and impression composition table  500  of  FIG. 5 . For age/gender groups missing from the table  500 , frequency values are taken from the ratings entity campaign-level age/gender and impression composition table  600  of  FIG. 6 . For example, the database proprietor campaign-level age/gender and impression composition table  500  does not have a less than 12 (&lt;12) age/gender group. Thus, a frequency value of 3 is taken from the ratings entity campaign-level age/gender and impression composition table  600 . 
     The reach column  808  stores reach values representing reach of one or more of the content and/or advertisements  102  ( FIG. 1 ) for each age/gender group. The reach values are determined by dividing respective impressions values from the impressions column  804  by corresponding frequency values from the frequency column  806 . The impressions composition column  810  stores values indicative of the percentage of impressions per age/gender group. In the illustrated example, the final total frequency in the frequency column  806  is equal to the total impressions divided by the total reach. 
       FIGS. 9, 10, 11, 12, and 14A-14B  are flow diagrams representative of machine readable instructions that can be executed to implement the methods and apparatus described herein. The example processes of  FIGS. 9, 10, 11, 12, and 14A-14B  may be implemented using machine readable instructions that, when executed, cause a device (e.g., a programmable controller, processor, other programmable machine, integrated circuit, or logic circuit) to perform the operations shown in  FIGS. 9, 10, 11, 12, and 14A-14B . For instance, the example processes of  FIGS. 9, 10, 11, 12, and 14A-14B  may be performed using a processor, a controller, and/or any other suitable processing device. For example, the example process of  FIGS. 9, 10, 11, 12 , and  14 A- 14 B may be implemented using coded instructions stored on a tangible machine readable medium such as a flash memory, a read-only memory (ROM), and/or a random-access memory (RAM). 
     As used herein, the term tangible computer readable medium is expressly defined to include any type of computer readable storage and to exclude propagating signals. Additionally or alternatively, the example processes of  FIGS. 9, 10, 11, 12 , and  14 A- 14 B may be implemented using coded instructions (e.g., computer readable instructions) stored on a non-transitory computer readable medium such as a flash memory, a read-only memory (ROM), a random-access memory (RAM), a cache, or any other storage media in which information is stored for any duration (e.g., for extended time periods, permanently, brief instances, for temporarily buffering, and/or for caching of the information). As used herein, the term non-transitory computer readable medium is expressly defined to include any type of computer readable medium and to exclude propagating signals. 
     Alternatively, the example processes of  FIGS. 9, 10, 11, 12, and 14A-14B  may be implemented using any combination(s) of application specific integrated circuit(s) (ASIC(s)), programmable logic device(s) (PLD(s)), field programmable logic device(s) (FPLD(s)), discrete logic, hardware, firmware, etc. Also, the example processes of  FIGS. 9, 10, 11, 12, and 14A-14B  may be implemented as any combination(s) of any of the foregoing techniques, for example, any combination of firmware, software, discrete logic and/or hardware. 
     Although the example processes of  FIGS. 9, 10, 11, 12, and 14A-14B  are described with reference to the flow diagrams of  FIGS. 9, 10, 11, 12, and 14A-14B , other methods of implementing the processes of  FIGS. 9, 10, 11, 12, and 14A-14B  may be employed. For example, the order of execution of the blocks may be changed, and/or some of the blocks described may be changed, eliminated, sub-divided, or combined. Additionally, one or both of the example processes of  FIGS. 9, 10, 11, 12, and 14A-14B  may be performed sequentially and/or in parallel by, for example, separate processing threads, processors, devices, discrete logic, circuits, etc. 
     Turning in detail to  FIG. 9 , the ratings entity subsystem  106  of  FIG. 1  may perform the depicted process to collect demographics and impression data from partners and to assess the accuracy and/or adjust its own demographics data of its panelists  114 ,  116 . The example process of  FIG. 9  collects demographics and impression data for registered users of one or more partners (e.g., the partners  206  and  208  of  FIGS. 2 and 3 ) that overlap with panelist members (e.g., the panelists  114  and  116  of  FIG. 1 ) of the ratings entity subsystem  106  as well as demographics and impression data from partner sites that correspond to users that are not registered panel members of the ratings entity subsystem  106 . The collected data is combined with other data collected at the ratings entity to determine online GRPs. The example process of  FIG. 9  is described in connection with the example system  100  of  FIG. 1  and the example system  200  of  FIG. 2 . 
     Initially, the GRP report generator  130  ( FIG. 1 ) receives impressions per unique users  235  ( FIG. 2 ) from the impression monitor system  132  (block  902 ). The GRP report generator  130  receives impressions-based aggregate demographics (e.g., the partner campaign-level age/gender and impression composition table  500  of  FIG. 5 ) from one or more partner(s) (block  904 ). In the illustrated example, user IDs of registered users of the partners  206 ,  208  are not received by the GRP report generator  130 . Instead, the partners  206 ,  208  remove user IDs and aggregate impressions-based demographics in the partner campaign-level age/gender and impression composition table  500  at demographic bucket levels (e.g., males aged 13-18, females aged 13-18, etc.). However, for instances in which the partners  206 ,  208  also send user IDs to the GRP report generator  130 , such user IDs are exchanged in an encrypted format based on, for example, the double encryption technique described above. 
     For examples in which the impression monitor system  132  modifies site IDs and sends the modified site IDs in the beacon response  306 , the partner(s) log impressions based on those modified site IDs. In such examples, the impressions collected from the partner(s) at block  904  are impressions logged by the partner(s) against the modified site IDs. When the ratings entity subsystem  106  receives the impressions with modified site IDs, GRP report generator  130  identifies site IDs for the impressions received from the partner(s) (block  906 ). For example, the GRP report generator  130  uses the site ID map  310  ( FIG. 3 ) generated by the impression monitor system  132  during the beacon receive and response process (e.g., discussed above in connection with  FIG. 3 ) to identify the actual site IDs corresponding to the modified site IDs in the impressions received from the partner(s). 
     The GRP report generator  130  receives per-panelist impressions-based demographics (e.g., the impressions-based panel demographics table  250  of  FIG. 2 ) from the panel collection platform  210  (block  908 ). In the illustrated example, per-panelist impressions-based demographics are impressions logged in association with respective user IDs of panelist  114 ,  116  ( FIG. 1 ) as shown in the impressions-based panel demographics table  250  of  FIG. 2 . 
     The GRP report generator  130  removes duplicate impressions between the per-panelist impressions-based panel demographics  250  received at block  908  from the panel collection platform  210  and the impressions per unique users  235  received at block  902  from the impression monitor system  132  (block  910 ). In this manner, duplicate impressions logged by both the impression monitor system  132  and the web client meter  222  ( FIG. 2 ) will not skew GRPs generated by the GRP generator  130 . In addition, by using the per-panelist impressions-based panel demographics  250  from the panel collection platform  210  and the impressions per unique users  235  from the impression monitor system  132 , the GRP generator  130  has the benefit of impressions from redundant systems (e.g., the impression monitor system  132  and the web client meter  222 ). In this manner, if one of the systems (e.g., one of the impression monitor system  132  or the web client meter  222 ) misses one or more impressions, the record(s) of such impression(s) can be obtained from the logged impressions of the other system (e.g., the other one of the impression monitor system  132  or the web client meter  222 ). 
     The GRP report generator  130  generates an aggregate of the impressions-based panel demographics  250  (block  912 ). For example, the GRP report generator  130  aggregates the impressions-based panel demographics  250  into demographic bucket levels (e.g., males aged 13-18, females aged 13-18, etc.) to generate the panelist ad campaign-level age/gender and impression composition table  600  of  FIG. 6 . 
     In some examples, the GRP report generator  130  does not use the per-panelist impressions-based panel demographics from the panel collection platform  210 . In such instances, the ratings entity subsystem  106  does not rely on web client meters such as the web client meter  222  of  FIG. 2  to determine GRP using the example process of  FIG. 9 . Instead in such instances, the GRP report generator  130  determines impressions of panelists based on the impressions per unique users  235  received at block  902  from the impression monitor system  132  and uses the results to aggregate the impressions-based panel demographics at block  912 . For example, as discussed above in connection with  FIG. 2 , the impressions per unique users table  235  stores panelist user IDs in association with total impressions and campaign IDs. As such, the GRP report generator  130  may determine impressions of panelists based on the impressions per unique users  235  without using the impression-based panel demographics  250  collected by the web client meter  222 . 
     The GRP report generator  130  combines the impressions-based aggregate demographic data from the partner(s)  206 ,  208  (received at block  904 ) and the panelists  114 ,  116  (generated at block  912 ) its demographic data with received demographic data (block  914 ). For example, the GRP report generator  130  of the illustrated example combines the impressions-based aggregate demographic data to form the combined campaign-level age/gender and impression composition table  700  of  FIG. 7 . 
     The GRP report generator  130  determines distributions for the impressions-based demographics of block  914  (block  916 ). In the illustrated example, the GRP report generator  130  stores the distributions of the impressions-based demographics in the age/gender impressions distribution table  800  of  FIG. 8 . In addition, the GRP report generator  130  generates online GRPs based on the impressions-based demographics (block  918 ). In the illustrated example, the GRP report generator  130  uses the GRPs to create one or more of the GRP report(s)  131 . In some examples, the ratings entity subsystem  106  sells or otherwise provides the GRP report(s)  131  to advertisers, publishers, content providers, manufacturers, and/or any other entity interested in such market research. The example process of  FIG. 9  then ends. 
     Turning now to  FIG. 10 , the depicted example flow diagram may be performed by a client computer  202 ,  203  ( FIGS. 2 and 3 ) to route beacon requests (e.g., the beacon requests  304 ,  308  of  FIG. 3 ) to web service providers to log demographics-based impressions. Initially, the client computer  202 ,  203  receives tagged content and/or a tagged advertisement  102  (block  1002 ) and sends the beacon request  304  to the impression monitor system  132  (block  1004 ) to give the impression monitor system  132  (e.g., at a first internet domain) an opportunity to log an impression for the client computer  202 ,  203 . The client computer  202 ,  203  begins a timer (block  1006 ) based on a time for which to wait for a response from the impression monitor system  132 . 
     If a timeout has not expired (block  1008 ), the client computer  202 ,  203  determines whether it has received a redirection message (block  1010 ) from the impression monitor system  132  (e.g., via the beacon response  306  of  FIG. 3 ). If the client computer  202 ,  203  has not received a redirection message (block  1010 ), control returns to block  1008 . Control remains at blocks  1008  and  1010  until either (1) a timeout has expired, in which case control advances to block  1016  or (2) the client computer  202 ,  203  receives a redirection message. 
     If the client computer  202 ,  203  receives a redirection message at block  1010 , the client computer  202 ,  203  sends the beacon request  308  to a partner specified in the redirection message (block  1012 ) to give the partner an opportunity to log an impression for the client computer  202 ,  203 . During a first instance of block  1012  for a particular tagged advertisement (e.g., the tagged advertisement  102 ), the partner (or in some examples, non-partnered database proprietor  110 ) specified in the redirection message corresponds to a second internet domain. During subsequent instances of block  1012  for the same tagged advertisement, as beacon requests are redirected to other partner or non-partnered database proprietors, such other partner or non-partnered database proprietors correspond to third, fourth, fifth, etc. internet domains. In some examples, the redirection message(s) may specify an intermediary(ies) (e.g., an intermediary(ies) server(s) or sub-domain server(s)) associated with a partner(s) and/or the client computer  202 ,  203  sends the beacon request  308  to the intermediary(ies) based on the redirection message(s) as described below in conjunction with  FIG. 13 . 
     The client computer  202 ,  203  determines whether to attempt to send another beacon request to another partner (block  1014 ). For example, the client computer  202 ,  203  may be configured to send a certain number of beacon requests in parallel (e.g., to send beacon requests to two or more partners at roughly the same time rather than sending one beacon request to a first partner at a second internet domain, waiting for a reply, then sending another beacon request to a second partner at a third internet domain, waiting for a reply, etc.) and/or to wait for a redirection message back from a current partner to which the client computer  202 ,  203  sent the beacon request at block  1012 . If the client computer  202 ,  203  determines that it should attempt to send another beacon request to another partner (block  1014 ), control returns to block  1006 . 
     If the client computer  202 ,  203  determines that it should not attempt to send another beacon request to another partner (block  1014 ) or after the timeout expires (block  1008 ), the client computer  202 ,  203  determines whether it has received the URL scrape instruction  320  ( FIG. 3 ) (block  1016 ). If the client computer  202 ,  203  did not receive the URL scrape instruction  320  (block  1016 ), control advances to block  1022 . Otherwise, the client computer  202 ,  203  scrapes the URL of the host website rendered by the web browser  212  (block  1018 ) in which the tagged content and/or advertisement  102  is displayed or which spawned the tagged content and/or advertisement  102  (e.g., in a pop-up window). The client computer  202 ,  203  sends the scraped URL  322  to the impression monitor system  132  (block  1020 ). Control then advances to block  1022 , at which the client computer  202 ,  203  determines whether to end the example process of  FIG. 10 . For example, if the client computer  202 ,  203  is shut down or placed in a standby mode or if its web browser  212  ( FIGS. 2 and 3 ) is shut down, the client computer  202 ,  203  ends the example process of  FIG. 10 . If the example process is not to be ended, control returns to block  1002  to receive another content and/or tagged ad. Otherwise, the example process of  FIG. 10  ends. 
     In some examples, real-time redirection messages from the impression monitor system  132  may be omitted from the example process of  FIG. 10 , in which cases the impression monitor system  132  does not send redirect instructions to the client computer  202 ,  203 . Instead, the client computer  202 ,  203  refers to its partner-priority-order cookie  220  to determine partners (e.g., the partners  206  and  208 ) to which it should send redirects and the ordering of such redirects. In some examples, the client computer  202 ,  203  sends redirects substantially simultaneously to all partners listed in the partner-priority-order cookie  220  (e.g., in seriatim, but in rapid succession, without waiting for replies). In such some examples, block  1010  is omitted and at block  1012 , the client computer  202 ,  203  sends a next partner redirect based on the partner-priority-order cookie  220 . In some such examples, blocks  1006  and  1008  may also be omitted, or blocks  1006  and  1008  may be kept to provide time for the impression monitor system  132  to provide the URL scrape instruction  320  at block  1016 . 
     Turning to  FIG. 11 , the example flow diagram may be performed by the impression monitor system  132  ( FIGS. 2 and 3 ) to log impressions and/or redirect beacon requests to web service providers (e.g., database proprietors) to log impressions. Initially, the impression monitor system  132  waits until it has received a beacon request (e.g., the beacon request  304  of  FIG. 3 ) (block  1102 ). The impression monitor system  132  of the illustrated example receives beacon requests via the HTTP server  232  of  FIG. 2 . When the impression monitor system  132  receives a beacon request (block  1102 ), it determines whether a cookie (e.g., the panelist monitor cookie  218  of  FIG. 2 ) was received from the client computer  202 ,  203  (block  1104 ). For example, if a panelist monitor cookie  218  was previously set in the client computer  202 ,  203 , the beacon request sent by the client computer  202 ,  203  to the panelist monitoring system will include the cookie. 
     If the impression monitor system  132  determines at block  1104  that it did not receive the cookie in the beacon request (e.g., the cookie was not previously set in the client computer  202 ,  203 , the impression monitor system  132  sets a cookie (e.g., the panelist monitor cookie  218 ) in the client computer  202 ,  203  (block  1106 ). For example, the impression monitor system  132  may use the HTTP server  232  to send back a response to the client computer  202 ,  203  to ‘set’ a new cookie (e.g., the panelist monitor cookie  218 ). 
     After setting the cookie (block  1106 ) or if the impression monitor system  132  did receive the cookie in the beacon request (block  1104 ), the impression monitor system  132  logs an impression (block  1108 ). The impression monitor system  132  of the illustrated example logs an impression in the impressions per unique users table  235  of  FIG. 2 . As discussed above, the impression monitor system  132  logs the impression regardless of whether the beacon request corresponds to a user ID that matches a user ID of a panelist member (e.g., one of the panelists  114  and  116  of  FIG. 1 ). However, if the user ID comparator  228  ( FIG. 2 ) determines that the user ID (e.g., the panelist monitor cookie  218 ) matches a user ID of a panelist member (e.g., one of the panelists  114  and  116  of  FIG. 1 ) set by and, thus, stored in the record of the ratings entity subsystem  106 , the logged impression will correspond to a panelist of the impression monitor system  132 . For such examples in which the user ID matches a user ID of a panelist, the impression monitor system  132  of the illustrated example logs a panelist identifier with the impression in the impressions per unique users table  235  and subsequently an audience measurement entity associates the known demographics of the corresponding panelist (e.g., a corresponding one of the panelists  114 ,  116 ) with the logged impression based on the panelist identifier. Such associations between panelist demographics (e.g., the age/gender column  602  of  FIG. 6 ) and logged impression data are shown in the panelist ad campaign-level age/gender and impression composition table  600  of  FIG. 6 . If the user ID comparator  228  ( FIG. 2 ) determines that the user ID does not correspond to a panelist  114 ,  116 , the impression monitor system  132  will still benefit from logging an impression (e.g., an ad impression or content impression) even though it will not have a user ID record (and, thus, corresponding demographics) for the impression reflected in the beacon request  304 . 
     The impression monitor system  132  selects a next partner (block  1110 ). For example, the impression monitor system  132  may use the rules/ML engine  230  ( FIG. 2 ) to select one of the partners  206  or  208  of  FIGS. 2 and 3  at random or based on an ordered listing or ranking of the partners  206  and  208  for an initial redirect in accordance with the rules/ML engine  230  ( FIG. 2 ) and to select the other one of the partners  206  or  208  for a subsequent redirect during a subsequent execution of block  1110 . 
     The impression monitor system  132  sends a beacon response (e.g., the beacon response  306 ) to the client computer  202 ,  203  including an HTTP  302  redirect (or any other suitable instruction to cause a redirected communication) to forward a beacon request (e.g., the beacon request  308  of  FIG. 3 ) to a next partner (e.g., the partner A  206  of  FIG. 2 ) (block  1112 ) and starts a timer (block  1114 ). The impression monitor system  132  of the illustrated example sends the beacon response  306  using the HTTP server  232 . In the illustrated example, the impression monitor system  132  sends an HTTP  302  redirect (or any other suitable instruction to cause a redirected communication) at least once to allow at least a partner site (e.g., one of the partners  206  or  208  of  FIGS. 2 and 3 ) to also log an impression for the same advertisement (or content). However, in other example implementations, the impression monitor system  132  may include rules (e.g., as part of the rules/ML engine  230  of  FIG. 2 ) to exclude some beacon requests from being redirected. The timer set at block  1114  is used to wait for real-time feedback from the next partner in the form of a fail status message indicating that the next partner did not find a match for the client computer  202 ,  203  in its records. 
     If the timeout has not expired (block  1116 ), the impression monitor system  132  determines whether it has received a fail status message (block  1118 ). Control remains at blocks  1116  and  1118  until either (1) a timeout has expired, in which case control returns to block  1102  to receive another beacon request or (2) the impression monitor system  132  receives a fail status message. 
     If the impression monitor system  132  receives a fail status message (block  1118 ), the impression monitor system  132  determines whether there is another partner to which a beacon request should be sent (block  1120 ) to provide another opportunity to log an impression. The impression monitor system  132  may select a next partner based on a smart selection process using the rules/ML engine  230  of  FIG. 2  or based on a fixed hierarchy of partners. If the impression monitor system  132  determines that there is another partner to which a beacon request should be sent, control returns to block  1110 . Otherwise, the example process of  FIG. 11  ends. 
     In some examples, real-time feedback from partners may be omitted from the example process of  FIG. 11  and the impression monitor system  132  does not send redirect instructions to the client computer  202 ,  203 . Instead, the client computer  202 ,  203  refers to its partner-priority-order cookie  220  to determine partners (e.g., the partners  206  and  208 ) to which it should send redirects and the ordering of such redirects. In some examples, the client computer  202 ,  203  sends redirects simultaneously to all partners listed in the partner-priority-order cookie  220 . In such some examples, blocks  1110 ,  1114 ,  1116 ,  1118 , and  1120  are omitted and at block  1112 , the impression monitor system  132  sends the client computer  202 ,  203  an acknowledgement response without sending a next partner redirect. 
     Turning now to  FIG. 12 , the example flow diagram may be executed to dynamically designate preferred web service providers (or preferred partners) from which to request logging of impressions using the example redirection beacon request processes of  FIGS. 10 and 11 . The example process of  FIG. 12  is described in connection with the example system  200  of  FIG. 2 . Initial impressions associated with content and/or ads delivered by a particular publisher site (e.g., the publisher  302  of  FIG. 3 ) trigger the beacon instructions  214  ( FIG. 2 ) (and/or beacon instructions at other computers) to request logging of impressions at a preferred partner (block  1202 ). In this illustrated example, the preferred partner is initially the partner A site  206  ( FIGS. 2 and 3 ). The impression monitor system  132  ( FIGS. 1, 2, and 3 ) receives feedback on non-matching user IDs from the preferred partner  206  (block  1204 ). The rules/ML engine  230  ( FIG. 2 ) updates the preferred partner for the non-matching user IDs (block  1206 ) based on the feedback received at block  1204 . In some examples, during the operation of block  1206 , the impression monitor system  132  also updates a partner-priority-order of preferred partners in the partner-priority-order cookie  220  of  FIG. 2 . Subsequent impressions trigger the beacon instructions  214  (and/or beacon instructions at other computers  202 ,  203 ) to send requests for logging of impressions to different respective preferred partners specifically based on each user ID (block  1208 ). That is, some user IDs in the panelist monitor cookie  218  and/or the partner cookie(s)  216  may be associated with one preferred partner, while others of the user IDs are now associated with a different preferred partner as a result of the operation at block  1206 . The example process of  FIG. 12  then ends. 
       FIG. 13  depicts an example system  1300  that may be used to determine media (e.g., content and/or advertising) exposure based on information collected by one or more database proprietors. The example system  1300  is another example of the systems  200  and  300  illustrated in  FIGS. 2 and 3  in which an intermediary  1308 ,  1312  is provided between a client computer  1304  and a partner  1310 ,  1314 . Persons of ordinary skill in the art will understand that the description of  FIGS. 2 and 3  and the corresponding flow diagrams of  FIGS. 8-12  are applicable to the system  1300  with the inclusion of the intermediary  1308 ,  1312 . 
     According to the illustrated example, a publisher  1302  transmits media (e.g., an advertisement and/or content) to the client computer  1304  in response to a request from a client computer (e.g., an HTTP request). The publisher  1302  may be the publisher  302  described in conjunction with  FIG. 3 . The client computer  1304  may be the panelist client computer  202  or the non-panelist computer  203  described in conjunction with  FIGS. 2 and 3  or any other client computer. The example client computer  1304  also provides a cookie supplied by the publisher  1302  to the publisher  1302  with the request (if the client computer  1304  has such a cookie). If the client computer does not have a cookie, the example publisher  1302  places a cookie on the client computer  1304 . The example cookie provides a unique identifier that enables the publisher  1302  to know when the client computer  1304  sends requests and enables the example publisher  1302  to provide media (e.g., advertising and/or content) more likely to be of interest to the example client computer  1304 . The media includes a beacon that instructs the client computer to send a request to an impression monitor  1306  as explained above. 
     The impression monitor  1306  may be the impression monitor system  132  described in conjunction with  FIGS. 1-3 . The impression monitor  1306  of the illustrated example receives beacon requests from the client computer  1304  and transmits redirection messages to the client computer  1304  to instruct the client to send a request to one or more of the intermediary A  1308 , the intermediary B  1312 , or any other system such as another intermediary, a partner, etc. The impression monitor  1306  also receives information about partner cookies from one or more of the intermediary A  1308  and the intermediary B  1312 . 
     In some examples, the impression monitor  1306  may insert into a redirection message an identifier of a client that is established by the impression monitor  1306  and identifies the client computer  1304  and/or a user thereof. For example, the identifier of the client may be an identifier stored in a cookie that has been set at the client by the impression monitor  1306  or any other entity, an identifier assigned by the impression monitor  1306  or any other entity, etc. The identifier of the client may be a unique identifier, a semi-unique identifier, etc. In some examples, the identifier of the client may be encrypted, obfuscated, or varied to prevent tracking of the identifier by the intermediary  1308 ,  1312  or the partner  1310 ,  1314 . According to the illustrated example, the identifier of the client is included in the redirection message to the client computer  1304  to cause the client computer  1304  to transmit the identifier of the client to the intermediary  1308 ,  1312  when the client computer  1304  follows the redirection message. For example, the identifier of the client may be included in a URL included in the redirection message to cause the client computer  1304  to transmit the identifier of the client to the intermediary  1308 ,  1312  as a parameter of the request that is sent in response to the redirection message. 
     The intermediaries  1308 ,  1312  of the illustrated example receive redirected beacon requests from the client computer  1304  and transmit information about the requests to the partners  1310 ,  1314 . The example intermediaries  1308 ,  1312  are made available on a content delivery network (e.g., one or more servers of a content delivery network) to ensure that clients can quickly send the requests without causing substantial interruption in the access of content from the publisher  1302 . 
     In examples disclosed herein, a cookie set in a domain (e.g., “partnerA.com”) is accessible by a server of a sub-domain (e.g., “intermediary.partnerA.com”) corresponding to the domain (e.g., the root domain “partnerA.com”) in which the cookie was set. In some examples, the reverse is also true such that a cookie set in a sub-domain (e.g., “intermediary.partnerA.com”) is accessible by a server of a root domain (e.g., the root domain “partnerA.com”) corresponding to the sub-domain (e.g., “intermediary.partnerA.com”) in which the cookie was set. As used herein, the term domain (e.g., Internet domain, domain name, etc.) is generic to (i.e., includes) the root domain (e.g., “domain.com”) and sub-domains (e.g., “a.domain.com,” “b.domain.com,” “c.d.domain.com,” etc.). 
     To enable the example intermediaries  1308 ,  1312  to receive cookie information associated with the partners  1310 ,  1314  respectively, sub-domains of the partners  1310 ,  1314  are assigned to the intermediaries  1308 ,  1312 . For example, the partner A  1310  may register an internet address associated with the intermediary A  1308  with the sub-domain in a domain name system associated with a domain for the partner A  1310 . Alternatively, the sub-domain may be associated with the intermediary in any other manner. In such examples, cookies set for the domain name of partner A  1310  are transmitted from the client computer  1304  to the intermediary A  1308  that has been assigned a sub-domain name associated with the domain of partner A  1310  when the client  1304  transmits a request to the intermediary A  1308 . 
     The example intermediaries  1308 ,  1312  transmit the beacon request information including a campaign ID and received cookie information to the partners  1310 ,  1314  respectively. This information may be stored at the intermediaries  1308 ,  1312  so that it can be sent to the partners  1310 ,  1314  in a batch. For example, the received information could be transmitted near the end of the day, near the end of the week, after a threshold amount of information is received, etc. Alternatively, the information may be transmitted immediately upon receipt. The campaign ID may be encrypted, obfuscated, varied, etc. to prevent the partners  1310 ,  1314  from recognizing the content to which the campaign ID corresponds or to otherwise protect the identity of the media. A lookup table of campaign ID information may be stored at the impression monitor  1306  so that impression information received from the partners  1310 ,  1314  can be correlated with the media. 
     The intermediaries  1308 ,  1312  of the illustrated example also transmit an indication of the availability of a partner cookie to the impression monitor  1306 . For example, when a redirected beacon request is received at the intermediary A  1308 , the intermediary A  1308  determines if the redirected beacon request includes a cookie for partner A  1310 . The intermediary A  1308  sends the notification to the impression monitor  1306  when the cookie for partner A  1310  was received. Alternatively, intermediaries  1308 ,  1312  may transmit information about the availability of the partner cookie regardless of whether a cookie is received. Where the impression monitor  1306  has included an identifier of the client in the redirection message and the identifier of the client is received at the intermediaries  1308 ,  1312 , the intermediaries  1308 ,  1312  may include the identifier of the client with the information about the partner cookie transmitted to the impression monitor  1306 . The impression monitor  1306  may use the information about the existence of a partner cookie to determine how to redirect future beacon requests. For example, the impression monitor  1306  may elect not to redirect a client to an intermediary  1308 ,  1312  that is associated with a partner  1310 ,  1314  with which it has been determined that a client does not have a cookie. In some examples, the information about whether a particular client has a cookie associated with a partner may be refreshed periodically or aperiodically to account for cookies expiring and new cookies being set (e.g., a recent login or registration at one of the partners). 
     The intermediaries  1308 ,  1312  may be implemented by a server associated with a metering entity (e.g., an audience measurement entity that provides the impression monitor  1306 ). Alternatively, intermediaries  1308 ,  1312  may be implemented by servers associated with the partners  1310 ,  1314  respectively. In other examples, the intermediaries may be provided by a third-party such as a content delivery network. 
     In some examples, the intermediaries  1308 ,  1312  are provided to prevent a direct connection between the partners  1310 ,  1314  and the client computer  1304 , to prevent some information from the redirected beacon request from being transmitted to the partners  1310 ,  1314  (e.g., to prevent a REFERRER_URL from being transmitted to the partners  1310 ,  1314 ), to reduce the amount of network traffic at the partners  1310 ,  1314  associated with redirected beacon requests, and/or to transmit to the impression monitor  1306  real-time or near real-time indications of whether a partner cookie is provided by the client computer  1304 . 
     In some examples, the intermediaries  1308 ,  1312  are trusted by the partners  1310 ,  1314  to prevent confidential data from being transmitted to the impression monitor  1306 . For example, the intermediary  1308 ,  1312  may remove identifiers stored in partner cookies before transmitting information to the impression monitor  1306 . 
     The partners  1310 ,  1314  receive beacon request information including the campaign ID and cookie information from the intermediaries  1308 ,  1312 . The partners  1310 ,  1314  determine identity and demographics for a user of the client computer  1304  based on the cookie information. The example partners  1310 ,  1314  track impressions for the campaign ID based on the determined demographics associated with the impression. Based on the tracked impressions, the example partners  1310 ,  1314  generate reports such as those previously described above. The reports may be sent to the impression monitor  1306 , the publisher  1302 , an advertiser that supplied an ad provided by the publisher  1302 , a media hub, and/or other persons or entities interested in the reports. 
     While the intermediaries  1308 ,  1312  are shown in  FIG. 13 , either or both of the intermediaries  1308 ,  1312  may be omitted in some examples. 
     In the example of  FIG. 13 , the partner A  1310  and partner B  1314  provide reports including aggregate audience and impression information to the impression monitor  1306 . The use of multiple partners  1310 ,  1314  in  FIG. 13  increases the chances that accurate demographics can be obtained for persons exposed to media. However, the audience and impression information provided by the partners  1310 ,  1314  may include duplicate audience members and/or duplicate impressions. Undetected duplication of audience members and/or impressions can cause overcounting of audience members and/or impressions. Such errors can result in attributing incorrect demographic characteristics to the impressions. 
     The example impression monitor  1306  of  FIG. 13  de-duplicates the impression information to increase the accuracy of the combined data. To perform de-duplication, the impression monitor  1306  of the illustrated example determines a correlation (e.g., proportion of overlap) between users of the partners  1310 ,  1314  (e.g., a portion of the users of first partner (e.g., partner A  1310 ) that are also users of the second partner (e.g., partner B  1314 ) using panel-based data. For example, the impression monitor  1306  of the illustrated example determines the correlation as a proportion of the panelist computers  202  that have stored a cookie associated with the first partner  1310  and also stored a cookie associated with second partner  1314 . The example impression monitor  1306  of  FIG. 13  uses the correlation to determine the duplicate impression information and/or to de-duplicate the impression information. The example impression monitor  1306  of  FIG. 13  includes a data collector  1316 , a panel data processor  1318 , a duplication estimator  1320 , and a de-duplicator  1322 . 
     The example data collector  1316  of  FIG. 13  collects universe estimates (e.g., from an audience research service or other census provider). The universe refers to the total population of one or more selected audience categories (e.g., demographic groups). Universe estimates may be generated using surveys (e.g., questionnaires) of a set of individuals. In some examples, the results of the surveys are weighted based on the characteristics of the respondents to the survey to estimate a total number of persons in the universe. In some examples, universe estimates are performed manually and the results are imported by the data collector  1316  (e.g., in a table or other data format). In some other examples, the tasks performed for generating the universe estimates are partially or completely automated. 
     The example data collector  1316  of  FIG. 13  also collects audience and/or impression information (e.g., aggregate unique audience members and impressions) from the partners  1310 ,  1314 . For example, the data collector  1316  of the illustrated example receives a number of unique audience members that were identified by the partner A  1310  during a time period, as described above, and a number of impressions associated with those audience members. Similarly, the example data collector  1316  receives a number of unique audience members that were identified by the partner B  1314  during the time period, as described above, and a number of impressions associated with those audience members. Because the partners  1310 ,  1314  can differentiate between their respective users, the partners  1310 ,  1314  determine unique audience members (e.g., by de-duplicating the audience and/or impression data collected by the respective partner) prior to sending the number of unique audience members to the data collector  1316 . However, the example partners  1310 ,  1314  do not know whether any audience members in their respective unique audiences overlap with unique members in the unique audience of the other partner(s). 
     The example data collector  1316  of  FIG. 13  also collects panel data. In the illustrated example, panel data includes numbers or proportions of panelists who have visited web pages and/or web sites associated with each of the partners  1310 ,  1314 , as well as information about the individual panelists associated with those visits to the web pages or web sites. For example, the data collector  1316  receives a number or proportion of panelists who have visited web page(s) and/or web site(s) at which partner A  1310  can identify the user, a number or proportion of panelists who have visited web page(s) and/or web site(s) at which partner B  1314  can identify the user, and a total number of panelists reporting. The data collector  1316  may receive the panel data directly and/or may derive the panel data from reports obtained from the panelists that describe the panelists&#39; online usage. 
     In the example of  FIG. 13 , the universe estimates, impression information, and panel data are split into designated demographic groupings such as age and gender groups (e.g., females 12-17, females 18-20, males 12-17, males 18-20, etc.). However, the data may be considered in aggregate or may be split according to any other desired division. Although demographic groups in the illustrated examples disclosed herein are based on age and gender, additional or alternative types of demographic characteristics (e.g., income, geographic location, ethnicity, occupation, etc.) may be used to form the demographic groups. 
     As described below, the example impression monitor  1306  of  FIG. 13  processes the received universe estimate, unique audience, impressions, and panel data to determine unduplicated audience, unduplicated impressions, unduplicated reach, and/or unduplicated frequency information. 
       FIG. 15  is a table  1500  illustrating example universe estimates that may be used by the impression monitor  1306  of  FIG. 13  to de-duplicate audience and/or impressions received from multiple database proprietors. The example table  1500  may be obtained by the data collector  1316  from a census provider. While the example table  1500  of  FIG. 15  includes universe estimates from two example sources (e.g., Source  1  and Source  2 ) having different frequencies of estimate updates, the data collector  1316  may receive one universe estimate or select between the universe estimates using one or more criteria. 
       FIG. 16  is a table  1600  illustrating example aggregate unique audience and impression data from a first database proprietor (e.g., Partner A  1310  of  FIG. 13 ) that may be used by the impression monitor  1306  of  FIG. 13  to de-duplicate audience and/or impressions received from multiple database proprietors  1310 ,  1314 . The example partner  1310  of  FIG. 13  provides the unique audience and number of impressions for each of the illustrated example demographic groups. This data is populated in the table  1600 . Similarly,  FIG. 17  is a table  1700  illustrating example aggregate unique audience and impression data from a second database proprietor (e.g., Partner B  1314  of  FIG. 13 ). 
     From the unique audiences, the impressions, and the universe estimates, the example panel data processor  1318  of the illustrated example calculates the reach and the frequency (e.g., frequency of impressions) of each of the demographic groups. In the example of  FIG. 13 , the frequency calculated by the panel data processor  1318  is a measured frequency because it is determined from the panel data. For example, the data processor  1318  of the illustrated example calculates reach as the percentage of the universe represented by the unique audience for the demographic group (e.g., 50,000/6,374,500=0.8% for the male 18-20 demographic group). The example panel data processor  1318  of  FIG. 13  calculates the frequency as the impressions per unique audience member (e.g., 160,000/50,000=3.2 for the male 18-20 demographic group). 
       FIG. 18  is a table  1800  illustrating example audience level proportions determined from a panel for multiple database proprietors (e.g., the partners  1310 ,  1314  of  FIG. 13 ) that may be used by the impression monitor  1306  of  FIG. 13  to de-duplicate audience and/or impressions received from multiple database proprietors. The example proportion information in  FIG. 18  is determined from cookie information obtained from the panelist computers  202  of  FIG. 13 . 
     The example proportions in the table  1800  of  FIG. 18  include the proportions of panelists and/or households associated with the panelist computers  202  that fall into one of four classifications: (a) panelists and/or households that do not have cookies associated with any partner  1310 ,  1314  on the panelist computer  202 , (b) panelists and/or households that have a cookie associated with a first one of the partners  1310  but not a second one of the partners  1314  on the panelist computer  202 , (c) panelists and/or households that have a cookie associated with the second one of the partners  1314  but not the first one of the partners  1310  on the panelist computer  202 , or (d) panelists and/or households that have cookies associated with both partners  1310 ,  1314  on the panelist computer  202 . Classifications (a), (b), and (c) of  FIG. 18  are portions of the panelists and/or households that do not overlap for the database proprietors. Classification (d) is the portion of the panelists and/or households that overlap, in that the panelists and/or households in classification (d) have cookies for both database proprietors. The example data processor  1318  of  FIG. 13  determines the proportions for each of the classifications (e.g., each of the columns of the table  1800 ) in a given demographic group (e.g., a row of the table  1800 ) by determining the demographic group(s) associated with the panelist computer  202  and determining a percentage of the panelist computers  202  that fall into each classification for the corresponding demographic group(s) (e.g., based on the cookies located on the respective panelist computers  202 ). Accordingly, the totals of the proportions from each column of the table  1800  are 1.00 for each demographic group in the example table  1800 . 
       FIG. 19  is a table  1900  illustrating example total unduplicated audience and impression data from 2 or more database proprietors (e.g., partners  1310 ,  1314  of  FIG. 13 ). The example impression monitor  1306  of  FIG. 13  uses the unduplicated audience and impression data of the table  1900  to de-duplicate the impression information. The example data processor  1318  of  FIG. 13  determines the unduplicated audience for each demographic group of  FIG. 19  by summing the unique audiences reported by the partners  1310 ,  1314  for that demographic group (e.g., the unique audiences illustrated in  FIGS. 16 and 17 ). Similarly, the example data processor  1318  determines the unduplicated impressions for each demographic group by summing the unduplicated impressions reported by the partners  1310 ,  1314  for that demographic group (e.g., the unique impressions illustrated in  FIGS. 16 and 17 ). The data processor  1318  of the illustrated example determines the unduplicated frequency by dividing the unduplicated impressions by the unduplicated audience for the corresponding demographic group. 
     The example duplication estimator  1320  of  FIG. 13  estimates a duplication of unique audience members and/or impressions between the partners  1310 ,  1314  for each of the demographic groups. The estimated duplication may be different for different demographic groups. Based on the estimated duplication, the example de-duplicator  1322  of  FIG. 13  de-duplicates the total unique audience, the total impressions, the reach, and/or the frequency for a campaign. 
     To estimate duplication (e.g., for a demographic group), the example duplication estimator  1320  of  FIG. 13  selects a method of de-duplication. In the example of  FIG. 13 , if the data received from the panel (e.g., the panelist computers  202 ) for a demographic group includes cookies associated with both partners  1310 ,  1314  (e.g., for columns (b)-(d) of  FIG. 18 , column (b)+column (d)&gt;0 for the selected demographic group and column (c)+column (d)&gt;0 for the selected demographic group), the example duplication estimator  1320  selects a modified Danaher method. For example, the female, 18-20, demographic group of  FIG. 18  has panel data representing partner A  1310  (e.g., column (b)=0.15 and column (d)=0.27, and 0.15+0.27=0.42, which is greater than 0) and has panel data representing partner B (e.g., column (c)=0.07 and column (d)=0.27, and 0.07+0.27=0.34, which is greater than 0), so the example duplication estimator  1320  of  FIG. 13  selects a modified Danaher method. If any of the database proprietors are not represented in the panel data, (e.g., for columns (b)-(d) of  FIG. 18 , column (b)+column (d)=0 for the selected demographic group or column (c)+column (d)=0 for the selected demographic group), the example duplication estimator  1320  selects another approach such as a random approach. The example random approach is described with reference to block  1424  of  FIG. 14B . 
       FIG. 20  is a table  2000  illustrating example correlation (e.g., proportion of overlap), example reach, example adjusted correlation (e.g., adjusted proportion of overlap), example duplicate reach, example duplicate audience, and example duplicate impression information determined by the audience measurement system of  FIG. 13  using the Danaher method. In the example of  FIG. 13 , the correlation referred to in Danaher is replaced by (e.g., implemented using) the overlap, or proportion of overlap, between the panelists, households, and/or panelist computers that have a cookie (or other identifier) associated with a first database proprietor and the panelists, households, and/or panelist computers that have a cookie (or other identifier) associated with one or more other database proprietors. In some examples, an overlap is determined between two database proprietors, such that performing de-duplication for audience and/or impressions for data from more than two database proprietors uses multiple correlation factors. The overlap or proportion of overlap is referred to in the examples as the correlation, because the overlap may be considered to reflect a correlation, with respect to a total number of users or panelists, between the use of a first partner web site and the user of a second partner web site. 
     As used herein, reach is the percentage of the universe represented by the unique audience. Reach may be determined for one or more demographic groups. As used herein, duplicate reach refers to a portion of the reach that is determined to already be represented in the reach. For example, for a reach of 0.50 having a duplicate reach of 0.10, the unduplicated reach is 0.40 and 0.10 of the unduplicated reach represents the same persons (e.g., the same portion or percentage of the universe) as the duplicate reach. As used herein, a duplicate impression refers to an impression (e.g., a specific media item being presented to a specific person) that is determined to already be represented in the impressions. For example, for 1,000 impressions for which there are 100 duplicate impressions, there are 900 unduplicated impressions. 100 of the unduplicated impressions represent the same impressions as the 100 duplicate impressions. As used herein, duplicate audience and duplicate unique audience refer to persons in the audience (e.g., a unique audience member, a specific person) who are determined to already be represented in the audience. As used herein, “unduplicated” refers to being substantially free (e.g., estimated to be free or determined to be free) of duplicates. For example, unduplicated reach refers to reach that is substantially free (estimated or determined to be free) of duplicate audience. 
     To estimate the duplication for the demographic group using the Danaher method, the example duplication estimator  1320  of  FIG. 13  determines a correlation between the reaches of the respective partners  1310 ,  1314 . For example, the duplication estimator  1320  may use Equation 4 below, in which the variables a, b, c, and d refer to the values in columns (a), (b), (c), and (d), respectively, of a single row (e.g., demographic group) in the table  1800  of  FIG. 18 . 
     
       
         
           
             
               
                 
                   Correlation 
                   = 
                   
                     
                       ad 
                       - 
                       bc 
                     
                     
                       
                         
                           ( 
                           
                             a 
                             + 
                             b 
                           
                           ) 
                         
                         ⁢ 
                         
                           ( 
                           
                             a 
                             + 
                             c 
                           
                           ) 
                         
                         ⁢ 
                         
                           ( 
                           
                             b 
                             + 
                             d 
                           
                           ) 
                         
                         ⁢ 
                         
                           ( 
                           
                             c 
                             + 
                             d 
                           
                           ) 
                         
                       
                     
                   
                 
               
               
                 
                   Equation 
                   ⁢ 
                   
                       
                   
                   ⁢ 
                   4 
                 
               
             
           
         
       
     
     For example, using the data illustrated in  FIG. 18 , the duplication estimator  1320  calculates the correlation for the male 18-20 demographic group to be (0.51*0.23−0.18*0.08)/SQRT((0.51+0.18)*(0.51+0.08)(0.18+0.23)*(D89+0.23))=0.46. 
     The example duplication estimator  1320  of  FIG. 13  calculates an adjusted correlation for the demographic group. In the example of  FIG. 13 , the duplication estimator  1320  determines a reach for partner  1310  based on the panel data (PanelReach 1  (PR 1 ) or Panel DP 1  reach of  FIG. 20 ) and determines a reach for partner  1314  based on the panel data (PanelReach 2  (PR 2 ) or Panel DP 2  reach of  FIG. 20 ). The example duplication estimator  1320  determines PR 1  to be the sum of the columns (b) and (d) of  FIG. 18  for the associated demographic group. Similarly, the duplication estimator  1320  determines PR 2  to be the sum of the columns (c) and (d) of  FIG. 18  for the associated demographic group. The example duplication estimator  1320  further determines the campaign-based reach for the partner A  1310  as CampaignReach 1  (CR 1 ) (from the reach column of  FIG. 16  for the demographic group) and determines the campaign-based reach for the partner B  1314  as CampaignReach 2  (CR 2 ) (from the reach column of  FIG. 17  for the demographic group). 
     The example duplication estimator  1320  of  FIG. 13  determines the adjusted correlation for each demographic group based on an adjustment factor (e.g., using PR 1 , PR 2 , CR 1 , and CR 2 ) and the calculated correlation for the demographic group. In the example of  FIG. 13 , the adjusted correlation is calculated differently (e.g., using a designated one of Equations 5-8 below) based on the relationship between PR 1  and CR 1  and the relationship between PR 2  and CR 2 . 
     
       
         
           
             
               
                 
                   
                     Adjusted 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     Correlation 
                   
                   = 
                   
                     { 
                     
                       
                         
                           if 
                           ⁢ 
                           
                               
                           
                           ⁢ 
                           PR 
                           ⁢ 
                           
                               
                           
                           ⁢ 
                           1 
                         
                         ≤ 
                         
                           CR 
                           ⁢ 
                           
                               
                           
                           ⁢ 
                           1 
                           ⁢ 
                           
                               
                           
                           ⁢ 
                           and 
                           ⁢ 
                           
                               
                           
                           ⁢ 
                           PR 
                           ⁢ 
                           
                               
                           
                           ⁢ 
                           2 
                         
                         ≤ 
                         
                           CR 
                           ⁢ 
                           
                               
                           
                           ⁢ 
                           2 
                         
                       
                       , 
                       
                         
 
                       
                       ⁢ 
                       
                         AdjustedCorrelation 
                         = 
                         
                           Correlation 
                           * 
                           
                             
                               
                                 PR 
                                 ⁢ 
                                 
                                     
                                 
                                 ⁢ 
                                 1 
                                 * 
                                 PR 
                                 ⁢ 
                                 
                                     
                                 
                                 ⁢ 
                                 2 
                                 ⁢ 
                                 
                                   ( 
                                   
                                     1 
                                     - 
                                     
                                       CR 
                                       ⁢ 
                                       
                                           
                                       
                                       ⁢ 
                                       1 
                                     
                                   
                                   ) 
                                 
                                 ⁢ 
                                 
                                   ( 
                                   
                                     1 
                                     - 
                                     
                                       CR 
                                       ⁢ 
                                       
                                           
                                       
                                       ⁢ 
                                       2 
                                     
                                   
                                   ) 
                                 
                               
                               
                                 
                                   ( 
                                   
                                     1 
                                     - 
                                     
                                       PR 
                                       ⁢ 
                                       
                                           
                                       
                                       ⁢ 
                                       1 
                                     
                                   
                                   ) 
                                 
                                 ⁢ 
                                 
                                   ( 
                                   
                                     1 
                                     - 
                                     
                                       PR 
                                       ⁢ 
                                       
                                           
                                       
                                       ⁢ 
                                       2 
                                     
                                   
                                   ) 
                                 
                                 ⁢ 
                                 CR 
                                 ⁢ 
                                 
                                     
                                 
                                 ⁢ 
                                 1 
                                 * 
                                 CR 
                                 ⁢ 
                                 
                                     
                                 
                                 ⁢ 
                                 2 
                               
                             
                           
                         
                       
                     
                   
                 
               
               
                 
                   Equation 
                   ⁢ 
                   
                       
                   
                   ⁢ 
                   5 
                 
               
             
             
               
                 
                   
                       
                   
                   ⁢ 
                   
                     
                       
                         if 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         PR 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         1 
                       
                       ≤ 
                       
                         CR 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         1 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         and 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         PR 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         2 
                       
                       &gt; 
                       
                         CR 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         2 
                       
                     
                     , 
                     
                       
 
                     
                     ⁢ 
                     
                       AdjustedCorrelation 
                       = 
                       
                         Correlation 
                         * 
                         
                           
                             
                               PR 
                               ⁢ 
                               
                                   
                               
                               ⁢ 
                               1 
                               ⁢ 
                               
                                 ( 
                                 
                                   1 
                                   - 
                                   
                                     PR 
                                     ⁢ 
                                     
                                         
                                     
                                     ⁢ 
                                     2 
                                   
                                 
                                 ) 
                               
                               * 
                               
                                 ( 
                                 
                                   1 
                                   - 
                                   
                                     CR 
                                     ⁢ 
                                     
                                         
                                     
                                     ⁢ 
                                     1 
                                   
                                 
                                 ) 
                               
                               ⁢ 
                               CR 
                               ⁢ 
                               
                                   
                               
                               ⁢ 
                               2 
                             
                             
                               
                                 ( 
                                 
                                   1 
                                   - 
                                   
                                     PR 
                                     ⁢ 
                                     
                                         
                                     
                                     ⁢ 
                                     1 
                                   
                                 
                                 ) 
                               
                               ⁢ 
                               PR 
                               ⁢ 
                               
                                   
                               
                               ⁢ 
                               2 
                               * 
                               CR 
                               ⁢ 
                               
                                   
                               
                               ⁢ 
                               1 
                               ⁢ 
                               
                                 ( 
                                 
                                   1 
                                   - 
                                   
                                     CR 
                                     ⁢ 
                                     
                                         
                                     
                                     ⁢ 
                                     2 
                                   
                                 
                                 ) 
                               
                             
                           
                         
                       
                     
                   
                 
               
               
                 
                   Equation 
                   ⁢ 
                   
                       
                   
                   ⁢ 
                   6 
                 
               
             
             
               
                 
                   
                       
                   
                   ⁢ 
                   
                     
                       
                         if 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         PR 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         1 
                       
                       &gt; 
                       
                         CR 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         1 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         and 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         PR 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         2 
                       
                       ≤ 
                       
                         CR 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         2 
                       
                     
                     , 
                     
                       
 
                     
                     ⁢ 
                     
                       AdjustedCorrelation 
                       = 
                       
                         Correlation 
                         * 
                         
                           
                             
                               
                                 ( 
                                 
                                   1 
                                   - 
                                   
                                     PR 
                                     ⁢ 
                                     
                                         
                                     
                                     ⁢ 
                                     1 
                                   
                                 
                                 ) 
                               
                               ⁢ 
                               PR 
                               ⁢ 
                               
                                   
                               
                               ⁢ 
                               2 
                               * 
                               CR 
                               ⁢ 
                               
                                   
                               
                               ⁢ 
                               1 
                               ⁢ 
                               
                                 ( 
                                 
                                   1 
                                   - 
                                   
                                     CR 
                                     ⁢ 
                                     
                                         
                                     
                                     ⁢ 
                                     2 
                                   
                                 
                                 ) 
                               
                             
                             
                               PR 
                               ⁢ 
                               
                                   
                               
                               ⁢ 
                               1 
                               ⁢ 
                               
                                 ( 
                                 
                                   1 
                                   - 
                                   
                                     PR 
                                     ⁢ 
                                     
                                         
                                     
                                     ⁢ 
                                     2 
                                   
                                 
                                 ) 
                               
                               ⁢ 
                               
                                 ( 
                                 
                                   1 
                                   - 
                                   
                                     CR 
                                     ⁢ 
                                     
                                         
                                     
                                     ⁢ 
                                     1 
                                   
                                 
                                 ) 
                               
                               ⁢ 
                               CR 
                               ⁢ 
                               
                                   
                               
                               ⁢ 
                               2 
                             
                           
                         
                       
                     
                   
                 
               
               
                 
                   Equation 
                   ⁢ 
                   
                       
                   
                   ⁢ 
                   7 
                 
               
             
             
               
                 
                   
                       
                   
                   ⁢ 
                   
                     
                       
                         if 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         PR 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         1 
                       
                       &gt; 
                       
                         CR 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         1 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         and 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         PR 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         2 
                       
                       &gt; 
                       
                         CR 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         2 
                       
                     
                     , 
                     
                       
 
                     
                     ⁢ 
                     
                       AdjustedCorrelation 
                       = 
                       
                         Correlation 
                         * 
                         
                           
                             
                               
                                 ( 
                                 
                                   1 
                                   - 
                                   
                                     PR 
                                     ⁢ 
                                     
                                         
                                     
                                     ⁢ 
                                     1 
                                   
                                 
                                 ) 
                               
                               ⁢ 
                               
                                 ( 
                                 
                                   1 
                                   - 
                                   
                                     PR 
                                     ⁢ 
                                     
                                         
                                     
                                     ⁢ 
                                     2 
                                   
                                 
                                 ) 
                               
                               ⁢ 
                               CR 
                               ⁢ 
                               
                                   
                               
                               ⁢ 
                               1 
                               * 
                               CR 
                               ⁢ 
                               
                                   
                               
                               ⁢ 
                               2 
                             
                             
                               PR 
                               ⁢ 
                               
                                   
                               
                               ⁢ 
                               1 
                               * 
                               PR 
                               ⁢ 
                               
                                   
                               
                               ⁢ 
                               2 
                               ⁢ 
                               
                                 ( 
                                 
                                   1 
                                   - 
                                   
                                     CR 
                                     ⁢ 
                                     
                                         
                                     
                                     ⁢ 
                                     1 
                                   
                                 
                                 ) 
                               
                               ⁢ 
                               
                                 ( 
                                 
                                   1 
                                   - 
                                   
                                     CR 
                                     ⁢ 
                                     
                                         
                                     
                                     ⁢ 
                                     2 
                                   
                                 
                                 ) 
                               
                             
                           
                         
                       
                     
                   
                   } 
                 
               
               
                 
                   Equation 
                   ⁢ 
                   
                       
                   
                   ⁢ 
                   8 
                 
               
             
           
         
       
     
     Using the adjusted correlation for the demographic group, the example duplication estimator  1320  of  FIG. 13  determines a duplicate reach for the demographic group. The example duplicate reach is shown in  FIG. 20  and may be determined using Equation 9 below. 
     
       
         
           
             
               
                 
                   
                     Duplicate 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     Reach 
                   
                   = 
                   
                     PR 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     1 
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                     PR 
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                     2 
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                         1 
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                             AdjCorr 
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                               ( 
                               
                                 1 
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                             ( 
                             
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                   9 
                 
               
             
           
         
       
     
     The duplication estimator  1320  of the illustrated example determines a duplicate audience and/or duplicate impressions based on the duplicate reach. For example, the duplication estimator  1320  of  FIG. 13  multiplies the duplicate reach by the universe estimate to determine (e.g., estimate) a number of unique audience members that are duplicated. The example duplication estimator  1320  multiplies the duplicate audience by the unduplicated frequency (e.g., the frequency of  FIG. 19 ) to determine the duplicate impressions. The example correlation, adjusted correlation, duplicate reach, duplicate audience, and duplicate impressions calculated using the values from  FIGS. 15-19  as explained above are illustrated in the table  2000  of  FIG. 20 . 
     After determining the duplicate impression information, the example de-duplicator  1322  of  FIG. 13  de-duplicates the impression information (e.g., the audience and/or the impressions) to generate unduplicated (or de-duplicated) impression information (e.g., de-duplicated unique audience, de-duplicated impressions, demographic information, etc.). For example, the de-duplicator  1322  subtracts the duplicate audience from the sum of the audiences of the database proprietors to determine the unduplicated audience. Similarly, the example de-duplicator  1322  of  FIG. 13  subtracts the duplicate impressions from the sum of the impressions of the database proprietors to determine the unduplicated impressions. 
       FIG. 21  is a table  2100  illustrating example duplicate reach, duplicate audience, and duplicate impression information determined by the impression monitor  1306  of  FIG. 13  using a random duplication approach. The example impression monitor  1306  of  FIG. 13  uses the random duplication approach when, for example, all or a portion of the panel does not have cookies associated with one or both of the partners  1310 ,  1314 . 
     The example duplication estimator  1320  of  FIG. 13  estimates a duplicate reach for a demographic group using the random duplication approach by multiplying the reach of the first partner  1310  (from  FIG. 16 ) and the reach of the second partner  1314  (from  FIG. 17 ). The duplication estimator  1320  multiplies the duplicate reach by the universe estimate to estimate a duplicate unique audience. The duplication estimator  1320  of the illustrated example determines the duplicate impressions by multiplying the duplicate unique audience by the frequency of  FIG. 19 . The example de-duplicator  1322  of  FIG. 13  de-duplicates the impression information as described above based on the duplicate unique audience and the duplicate impressions. 
     The example duplication estimator  1320  of  FIG. 13  calculates the duplicate audience and the duplicate impressions of  FIGS. 20 and 21  based on the monthly universe estimate associated with the panel data from  FIG. 15 . By using the monthly universe estimate, the example duplication estimator  1320  uses a same scale as for calculating the example correlation, the example reach of the database proprietors in the panel, the example adjusted correlation, and the example duplicated reach of  FIGS. 20 and 21 . In contrast, the example de-duplicator  1322  of  FIG. 13  refers to an annual universe estimate to determine the unduplicated reach in the example table  2200  of  FIG. 22 . By using the universe estimate that is determined independently from the panel data, the example de-duplicator  1322  may achieve a more accurate calculation of an audience for a media campaign (e.g., a calculation that is scaled independently from the panel estimates). 
       FIG. 22  is a table  2200  illustrating example unduplicated audience, example impression, example reach, and example frequency information determined by the impression monitor  1306  of  FIG. 13 . The example impression monitor  1306  determines an unduplicated audience by subtracting the duplicate unique audience of  FIG. 21  from the total audience of  FIG. 19  (e.g., the sum of the unique audiences from the partners  1310 ,  1314 ). Similarly, the example impression monitor  1306  determines unduplicated impressions by subtracting the duplicate impressions of  FIG. 21  from the total impressions of  FIG. 19  (e.g., the sum of the impressions from the partners  1310 ,  1314 ). 
     Using the unduplicated audience and unduplicated impressions, the example impression monitor  1306  of  FIG. 13  determines the reach and frequency of the unduplicated impression information. The example impression monitor  1306  of the illustrated example determines the reach by dividing the unduplicated audience by the universe estimate. The example impression monitor  1306  of  FIG. 13  determines the frequency by dividing the unduplicated impressions by the unduplicated audience. 
     The resulting table  2200  of  FIG. 22  provides the audience and impression information for a media campaign based on data received from multiple database proprietors. By de-duplicating the impression information as described herein, the example impression monitor  1306  of  FIG. 13  provides a more accurate report regarding the relative representations of the demographic groups (e.g., by utilizing the demographic knowledge of multiple database proprietors and by reducing overcounting of some demographic groups more than others). The example impression monitor  1306  of  FIG. 13  also reduces overall overcounting of audience and/or impressions for the media campaign, thereby more accurately representing the level of success of the media campaign. 
     While an example manner of implementing the impression monitor  1306  is illustrated in  FIG. 13 , one or more of the elements, processes and/or devices illustrated in  FIG. 13  may be combined, divided, re-arranged, omitted, eliminated and/or implemented in any other way. Further, the example data collector  1316 , the example panel data processor  1318 , the example duplication estimator  1320 , the example de-duplicator  1322  and/or, more generally, the example impression monitor  1306  of  FIG. 13  may be implemented by hardware, software, firmware and/or any combination of hardware, software and/or firmware. Thus, for example, any of the example data collector  1316 , the example panel data processor  1318 , the example duplication estimator  1320 , the example de-duplicator  1322  and/or, more generally, the example impression monitor  1306  could be implemented by one or more analog or digital circuit(s), logic circuits, programmable processor(s), application specific integrated circuit(s) (ASIC(s)), programmable logic device(s) (PLD(s)) and/or field programmable logic device(s) (FPLD(s)). When reading any of the apparatus or system claims of this patent to cover a purely software and/or firmware implementation, at least one of the example data collector  1316 , the example panel data processor  1318 , the example duplication estimator  1320 , and/or the example de-duplicator  1322  is/are hereby expressly defined to include a tangible computer readable storage device or storage disk such as a memory, a digital versatile disk (DVD), a compact disk (CD), a Blu-ray disk, etc. storing the software and/or firmware. Further still, the example ratings entity subsystem  106  of  FIGS. 1 and 2  may include one or more elements, processes and/or devices in addition to, or instead of, those illustrated in  FIGS. 1 and 2 , and/or may include more than one of any or all of the illustrated elements, processes and devices. 
       FIGS. 14A and 14B  collectively illustrate a flowchart representative of example machine readable instructions  1400  that may be executed to implement the example impression monitor  1306  of  FIG. 13  to de-duplicate audience and/or impression information received from multiple database proprietors (e.g., partners  1310 ,  1314  of  FIG. 13 ). The example instructions  1400  are described below with reference to an example one of the demographic groups used in the example tables of  FIGS. 15-22 . The instructions  1400  may be executed (e.g., in an iterative form) for additional groups. However, the instructions  1400  may be applied to any other demographic group, division of audience members, or to the undivided impression information. 
     The example impression monitor  1306  of  FIG. 13  (e.g., via the data collector  1316 ) determines a universe estimate for the demographic group (block  1402 ). For example, the data collector  1316  may request and/or receive one or more universe estimates of estimated total numbers of persons in the demographic group in a population. In some examples, the universe estimate is limited to a population within a geographic area of interest. 
     The example data collector  1316  of  FIG. 13  receives first impression information (e.g., a number of impressions, a number of unique audience members, and/or associated demographic information for the impressions) from a first database proprietor (e.g., the partner  1310 ) (block  1404 ). For example, the data collector  1316  may receive impression information represented by the table  1600  of  FIG. 16 . The example data processor  1318  calculates reach and/or frequency information from the first impression information (block  1406 ). The example data collector  1316  also receives second impression information from a second database proprietor (e.g., partner  1314 ) (block  1408 ). For example, the data collector  1316  may receive impression information represented by the table  1700  of  FIG. 17 . The example data processor  1318  also calculates reach and/or frequency information from the second impression information (block  1410 ). In some examples, the data collector  1316  receives impression information from additional database proprietors and/or the data processor  1318  determines the reach and/or frequency from the second impression information. 
     The example data processor  1318  of  FIG. 13  calculates audience proportions based on a panel (e.g., information from the panelist computers  202  of  FIG. 2 ) (block  1412 ). For example, the data processor  1318  may calculate the proportions of the audience having cookies for one or more of the partners  1310 ,  1314  to generate the data in the table  1800  of  FIG. 18 . As an example, the data processor  1318  determines the value of column (b) for a demographic group to be the proportion of the panelist computers  202  on which a cookie associated with partner A  1310  was identified and a cookie associated with partner B  1314  was not identified. 
     The example de-duplicator  1322  of  FIG. 13  determines whether both database proprietors (partners  1310 ,  1314 ) are represented in the audience proportion (block  1414 ). A database proprietor is considered to be represented in the panel when at least a threshold number of panelist computers  202  include cookies for the database proprietor. For example, the de-duplicator  1322  may determine whether the sum of columns (b) and (d) of  FIG. 18  (e.g., representative of cookies associated with the partner A  1310  being identified in the panelist computers) and the sum of columns (c) and (d) of  FIG. 18  (e.g., representative of cookies associated with the partner B  1314  being identified in the panelist computers) are both greater than 0. If both database proprietors are represented (block  1414 ), the example de-duplicator  1322  estimates the correlation (e.g., proportion of overlap) of users between the first and second database proprietor audiences from the panel audience proportions (block  1416 ). For example, the de-duplicator  1322  may determine the correlation and/or the adjusted correlation (e.g., adjusted proportion of overlap) between the database proprietors using Equations 2, 4, 5, 6, 7, and/or 8 as described above. 
     The example de-duplicator  1322  determines the duplicate reach based on the correlation and the reach of the database proprietors (block  1418 ). For example, the de-duplicator  1322  may use Equation 9 to determine the duplicate reach. 
     Returning to block  1414 , if one or more database proprietors are not represented in the audience proportion, the example de-duplicator  1322  determines the duplicate audience and/or duplicate impressions using another method, such as a random duplication method. Turning to  FIG. 14B , in the example random duplication approach, the de-duplicator  1322  determines a duplicate reach by multiplying the reach of the first database proprietor by the reach of the second database proprietor (block  1424 ). Control may then proceed to block  1420  of  FIG. 14A  to continue determining the duplicate audience and/or the duplicate impressions based on the duplicate reach. 
     Returning to  FIG. 14A , the de-duplicator  1322  of the illustrated example determines a duplicate audience and/or duplicate impressions based on the duplicate reach (block  1420 ). For example, the de-duplicator  1322  multiplies the duplicate reach by the universe estimate to determine a number of unique audience members that are duplicated. The de-duplicator  1322  multiplies the duplicate audience by the unduplicated frequency to determine the duplicate impressions. Example correlation values, example adjusted correlation values, example duplicate reach values, example duplicate audience values, and example duplicate impression values are illustrated in the table  2000  of  FIG. 20 . 
     The example de-duplicator  1322  de-duplicates the impression information (e.g., the audience and/or the impression) (block  1422 ). For example, the de-duplicator  1322  subtracts the duplicate audience from the sum of the audiences of the database proprietors to determine the unduplicated audience. Similarly, the example de-duplicator  1322  subtracts the duplicate impressions from the sum of the impressions of the database proprietors to determine the unduplicated impressions. 
     After de-duplicating the impression information, the example instructions  1400  end. In other examples, the example instructions  1400  return control to block  1402  to iterate for another demographic group. 
       FIG. 23  is a block diagram of an example processor system  2310  that may be used to implement the example impression monitor system  132 , the example rules/ML engine  230 , the example HTTP server communication interface  232 , the example publisher/campaign/user target database  232 , the example GRP report generator  130 , the example panel collection platform  210 , the example collector  117 , the example loader  118 , the example ratings entity database  120 , the example panelist computer(s)  202 , the example client computer  1304 , the example impression monitor  1306 , the example data collector  1316 , the example panel data processor  1318 , the example duplication estimator  1320 , and/or the example de-duplicator  1322  disclosed herein. As shown in  FIG. 23 , the processor system  2310  includes a processor  2312  that is coupled to an interconnection bus  2314 . The processor  2312  may be any suitable processor, processing unit, or microprocessor. Although not shown in  FIG. 23 , the system  2310  may be a multi-processor system and, thus, may include one or more additional processors that are identical or similar to the processor  2312  and that are communicatively coupled to the interconnection bus  2314 . 
     The processor  2312  of  FIG. 23  is coupled to a chipset  2318 , which includes a memory controller  2320  and an input/output (I/O) controller  2322 . A chipset provides I/O and memory management functions as well as a plurality of general purpose and/or special purpose registers, timers, etc. that are accessible or used by one or more processors coupled to the chipset  2318 . The memory controller  2320  performs functions that enable the processor  2312  (or processors if there are multiple processors) to access a system memory  2324 , a mass storage memory  2325 , and/or an optical media  2327 . 
     In general, the system memory  2324  may include any desired type of volatile and/or non-volatile memory such as, for example, static random access memory (SRAM), dynamic random access memory (DRAM), flash memory, read-only memory (ROM), etc. The mass storage memory  2325  may include any desired type of mass storage device including hard disk drives, optical drives, tape storage devices, etc. The optical media  2327  may include any desired type of optical media such as a digital versatile disc (DVD), a compact disc (CD), or a blu-ray optical disc. The instructions of any of  FIGS. 9-12 and/or 14A-14B  may be stored on any of the tangible media represented by the system memory  2324 , the mass storage device  2325 , and/or any other media. 
     The I/O controller  2322  performs functions that enable the processor  2312  to communicate with peripheral input/output (I/O) devices  2326  and  2328  and a network interface  2330  via an I/O bus  2332 . The I/O devices  2326  and  2328  may be any desired type of I/O device such as, for example, a keyboard, a video display or monitor, a mouse, etc. The network interface  2330  may be, for example, an Ethernet device, an asynchronous transfer mode (ATM) device, an 802.11 device, a digital subscriber line (DSL) modem, a cable modem, a cellular modem, etc. that enables the processor system  1310  to communicate with another processor system (e.g., via a network such as the Internet  104  of  FIG. 1 ). 
     While the memory controller  2320  and the I/O controller  2322  are depicted in  FIG. 23  as separate functional blocks within the chipset  2318 , the functions performed by these blocks may be integrated within a single semiconductor circuit or may be implemented using two or more separate integrated circuits. 
     Although the foregoing discloses the use of cookies for transmitting identification information from clients to servers, any other system for transmitting identification information from clients to servers or other computers may be used. For example, identification information or any other information provided by any of the cookies disclosed herein may be provided by an Adobe Flash® client identifier, identification information stored in an HTML5 datastore, an identifier used specifically for tracking advertising or other media (e.g., an AdID), etc. The methods and apparatus described herein are not limited to implementations that employ cookies. 
     Although certain example methods, apparatus and articles of manufacture have been disclosed herein, the scope of coverage of this patent is not limited thereto. On the contrary, this patent covers all methods, apparatus and articles of manufacture fairly falling within the scope of the claims of this patent.