CLUSTER

BOX

4%

CURB

8%

READ AND RESPOND RATES

(self-reported)

DOOR

16%

RARC Report

Report Number 

RARC-WP-15-009

Modes of 

Delivery and 

Customer 

Engagement 

with Advertising 

Mail

April 20, 2015
Executive 

Summary

Advertising mail delivered to a recipient’s door generates higher 

“read and response” rates than advertising mail delivered to 

the curbside or a neighborhood cluster box. Door delivery 

customers also are less likely to throw their ad mail away than 

customers with curb or cluster box delivery. 

These are among the key findings of a survey of 5,000 household 

mail recipients commissioned by the U.S. Postal Service Office 

of Inspector General (OIG) and conducted by InfoTrends, Inc. 

The degree of recipient engagement varied from one type of 

advertising mail to another.

Professor Michael Bradley of George Washington University 

analyzed the survey data. To control for the possibility that 

some other variable, such as gender or recipient use of the 

Internet, was not at play, Dr. Bradley performed statistical tests 

for relevant subgroups of the sample. He found no evidence 

that other defined variables were driving the results. Also, 

together with the OIG, Dr. Bradley analyzed data from two other 

U.S. Postal Service surveys. This analysis corroborated findings 

from the OIG/InfoTrends survey. 

This paper examines only recipients’ reported preferences; 

it does not reflect their actual behavior or explain its underlying 

causes. Nor does this paper discuss potential financial impacts 

on the Postal Service. We suggest that the Postal Service work 

closely with advertising mailers to better understand customer 

attitudes, their underlying causes, and any potential detrimental 

impacts on mail demand.

Highlights

The OIG, working with InfoTrends, surveyed 

5,000 households across the country to 

help determine their engagement with 

advertising mail.

Customer engagement with advertising 

mail varies with mode of delivery. 

Door delivery customers report higher 

levels of engagement with advertising mail 

than those who receive their mail through a 

curb or neighborhood cluster box.

Analyses of data from two Postal Service 

surveys reveal a general consistency with the 

results from the OIG-InfoTrends survey, which 

was analyzed by Professor Michael Bradley.

Centralized delivery will lower Postal Service 

delivery costs, but could have implications 

on the demand side. We suggest that the 

Postal Service and advertising mailers work 

together to understand these potential impacts. 

1

Modes of Delivery and Customer Engagement 

with Advertising Mail

Report Number RARC-WP-15-009
Table of Contents Cover

Executive Summary..........................................................................................................1

OIG Synopsis ...................................................................................................................3

Introduction .................................................................................................................3

Strategic Importance of Advertising Mail.....................................................................3

Methodology ...............................................................................................................3

Findings ......................................................................................................................4

Conclusions and Suggestions.....................................................................................6

Detailed Analysis ..............................................................................................................7

A. Introduction.............................................................................................................8

B. The OIG - InfoTrends Survey .................................................................................8

1. Survey Design ...................................................................................................8

2. Responses by Current Delivery Mode...............................................................9

3. Profile of Participants ......................................................................................10

C. Cluster Box Recipients’ Interactions with Advertising Mail Are Different ..............12

1. General Observations .....................................................................................12

2. Observations by Type of Advertising Mail .......................................................14

3. Hypothesis Testing ..........................................................................................20

a. Cluster Box and Door Read and Respond Rates ......................................20

b. Cluster Box and Door Discard Rates.........................................................22

c. Cluster Box and Curb Recipients...............................................................23

d. Cluster Box and Curb Tests .......................................................................27

D. Evidence from Other Surveys ..............................................................................29

1. Alternative Sources of Data.............................................................................29

a. Mail Moment Survey ..................................................................................30

b. Household Diary Recruitment Questionnaire ............................................32

2. Summary of Investigation of Alternative Sources............................................33

E. Exploring Other Possible Reasons for the Results...............................................33

1. General Attitudes Towards Advertising Mail ....................................................33

2. Responses by Gender.....................................................................................35

3. Responses by Internet Access ........................................................................36

4. Responses by Population Density...................................................................37

5. Responses by Residential Type ......................................................................41

F. Conclusion ...........................................................................................................41

Survey Questionnaire.....................................................................................................42

Contact Information ........................................................................................................48

Modes of Delivery and Customer Engagement 

with Advertising Mail

Report Number RARC-WP-15-009 2
OIG Synopsis Introduction

Postal delivery costs vary greatly by mode. Deliveries to neighborhood cluster box units are less expensive than curbside 

deliveries and are substantially less expensive than delivery to the door. The reason is obvious: carriers can avoid the time and 

expense of moving through a neighborhood when delivering the mail. The U.S. Postal Service Office of Inspector General (OIG) 

quantified the cost savings in an audit report in 2011.1

 This report addresses a different, yet equally important strategic question: 

does mode of delivery affect the recipient’s engagement with the mail? In particular, this paper analyzes whether mode of delivery 

has any effect on recipients’ stated engagement with advertising mail.

Strategic Importance of Advertising Mail

Advertising mail is of great strategic importance to the Postal Service. In 2013, Postal Service products generated $28.2 billion 

in contribution to institutional cost. The OIG estimates that 23 percent of this total, $6.3 billion, came from advertising mail sent 

to households.2

 According to the Boston Consulting Group, the Postal Service can expect the non-advertising component of 

First-Class Mail volume, its main source of contribution to institutional cost, to decline significantly by 2020. This inexorable change 

will force the Postal Service to rely increasingly on other products, including advertising mail, as well as cost-cutting to fund its 

operations.3

The Postal Service, like other postal operators, is considering moving delivery, to the extent possible, away from the door to 

curbside and cluster boxes.4

 However, door delivery is convenient for customers and is likely to be viewed as an entitlement by 

current door-delivery customers. This paper looks at a more nuanced aspect of this convenience. Simply stated: do door-delivery 

customers have a higher level of engagement with advertising mail? Do they read their advertising mail with a higher degree of 

frequency? This leads to a further question (not directly considered in this paper): could moving door-delivery customers to cluster 

boxes or curbside ultimately cause a decrease in mailing volumes? This is important because, despite cost savings on the delivery 

side, it is possible that such a decrease on the demand side could potentially put advertising mail’s contribution to Postal Service 

institutional costs in jeopardy.

Methodology

To investigate the issue of mail engagement, the OIG retained InfoTrends, Inc., a survey research firm, to conduct a survey of 

5,000 U.S. households. The survey methodology design ensured that respondents mirrored key demographic characteristics of 

the U.S. population. Ninety percent of respondents had Internet access and used the Internet to participate. The remaining 10 percent 

of respondents did not have Internet access and were contacted by phone. To analyze the survey data, the OIG retained 

Professor Michael Bradley of the George Washington University. Dr. Bradley’s analysis is summarized in the Detailed Analysis. 

The OIG worked closely with InfoTrends and Dr. Bradley to design a survey questionnaire that would address the key issues of interest. 

In addition to the OIG/InfoTrends data, the OIG asked Dr. Bradley to examine data from the Postal Service’s 2012 Mail Moment 

survey and the 2014 Household Diary Study recruitment questionnaire to see if these data supported the OIG/InfoTrends findings. 

1 U.S. Postal Service Office of the Inspector General, Audit Report – Modes of Delivery, Report Number DR-AR-11-006, July 7, 2011, 

https://www.uspsoig.gov/sites/default/files/document-library-files/2013/dr-ar-11-006.pdf. 

2 OIG calculation using data from three Postal Service sources from U.S. Postal Service, FY 2013 Public Cost and Revenue Analysis, Report Number USPS-FY13-1, 

December 27, 2013, http://www.prc.gov/dockets/document/88658; Postal Service, The Household Diary Study, May 2014, 

http://www.prc.gov/sites/default/files/uspsreports/USPS_HDS_FY13.pdf; and Postal Service, Market Dominant Billing Determinants, Report Number USPS-FY13-4, 

December 27, 2013, http://www.prc.gov/dockets/document/88662. 

3 The Boston Consulting Group, Projecting US Mail Volumes to 2020, Final Report – Detail, March 2, 2010, 

https://about.usps.com/future-postal-service/bcg-detailedpresentation.pdf.

4 Canada Post, Five Point Action Plan, December 2013, http://www.canadapost.ca/cpo/mc/assets/pdf/aboutus/5_en.pdf.

Modes of Delivery and Customer Engagement 

with Advertising Mail

Report Number RARC-WP-15-009 3
The OIG/InfoTrends survey asked about customer engagement with seven kinds of advertising mail:

1. Advertising mail from local companies I do business with.

2. Advertising mail from national companies I do business with.

3. Advertising mail from companies I do not do business with.

4. Donation Solicitations.

5. Credit Card Solicitations.

6. Catalogs.

7. Mail that includes a coupon.

To determine their engagement with the mail, recipients were asked how they handled the advertising mail they received. 

The options were:

1. Read and respond to the mail.

2. Read and throw away the mail.

3. Set the mail aside for later use.

4. Throw away the mail without reading it.

It is important to note that the survey results indicate what customers report they would do, not their actual behavior. 

Findings

The key findings of this research are:

■ For most kinds of advertising mail, mode of delivery has a significant impact on customer engagement. Customers who receive 

their advertising mail at their door are less likely to throw it away without reading it. Door-delivery customers are also more 

likely to read and respond to their advertising mail.

■ There are two exceptions to these findings:

● When advertising mail contains a coupon, customers “toss without reading” at the same rate, regardless of delivery mode. 

● Similar results held for advertising mail that came from a local company with which the customer had a pre-existing 

business relationship.

4

Modes of Delivery and Customer Engagement 

with Advertising Mail

Report Number RARC-WP-15-009
■ For some kinds of advertising mail, mode of delivery makes an enormous difference in customer engagement. 

● Respondents who received mail at the door said that they will read and respond to credit card solicitations at the rate of 

10.6 percent. The read and response rate drops by 70 percent, to 3.1 percent, when a cluster box is the mode of delivery. 

Respondents said that they would toss 59.2 percent of credit card solicitations without reading when they received them via 

a cluster box. The percentage reduced to 40.2 percent when delivery was made to the door.

● Responses to the remaining four categories were qualitatively similar to the credit card solicitation results, albeit with less 

dramatic differences by mode. 

■ Cluster box customers found their mail delivery location to be less convenient than either curbside or door delivery customers.

■ Most customers (63.3 percent) who currently do not have cluster box delivery say they would be displeased if their delivery was 

moved to a cluster box. Only 17.2 percent indicate they would be pleased by such a move.5

■ Dr. Bradley analyzed whether other factors besides delivery mode might be causing the results above. He examined whether 

numerous other variables such as attitude toward advertising mail, age of respondent, household income, population density, 

gender, and Internet use could have played a role in his findings. He concluded that none of these factors in the survey could 

explain the results.

■ Because cost savings for curbside delivery compared to door delivery are significant, Dr. Bradley repeated the analysis to 

compare curbside customers with cluster box customers. Curbside customers reported somewhat higher “read and respond” 

rates to advertising from local merchants with which they had done business and to advertising that contains a coupon. In 

addition, curbside customers reported that they were less inclined to throw away catalogs without reading them. Otherwise, the 

survey showed that curbside customers’ self-reported engagement with advertising mail is similar to that of cluster box customers. 

Analysis of the Mail Moment and Household Diary Study data supported these findings. 

■ Mail Moment survey cluster box respondents pick up their mail with less frequency than do respondents with other modes 

of delivery. Only 62.5 percent of cluster box customers picked up their mail at the first opportunity; compared to 93.9 percent 

of door customers and 87.7 percent of curbside recipients. In this regard, curbside and door customers report more similar 

behavior than curbside and cluster box recipients. 

■ According to the Mail Moment data, cluster box recipients were significantly less likely to keep their advertising mail and 

significantly more likely to discard it without reading. Similar, although less marked differences, were found in the Household 

Diary Study data.

These results reflect variations in customer response data. We caution the reader that extended inferences concerning causality 

can be problematic. Because we are working with survey data, we are not claiming to be investigating causality. Rather, we are 

examining stated postal customers’ actions and reactions. This examination revealed differences between cluster box and door 

recipients. Although the survey design and analyses controlled for other factors, we have not constructed a causal model of cluster 

5 Although the survey did not ask why customers would prefer cluster box delivery, previous OIG qualitative research indicated that these customers are concerned about 

the security of their mail. See OIG, What America Wants and Needs from the Postal Service, Report Number RARC-WP-14-009, February 18, 2014, 

https://www.uspsoig.gov/sites/default/files/document-library-files/2014/rarc-wp-14-009_1.pdf.

5

Modes of Delivery and Customer Engagement 

with Advertising Mail

Report Number RARC-WP-15-009
box recipients’ interactions with advertising mail and do not claim to have done so. Further work would be useful in identifying 

causal explanations of customer behavior by mode of delivery. 

It should also be noted that we surveyed customers about existing modes. Our survey results imply, but do not definitively 

conclude, that door delivery customers who are converted to cluster box or curbside delivery will adopt the same behaviors and 

attitudes toward advertising mail as current cluster box or curbside customers. The survey found that over 60 percent of recipients 

said they would be displeased if their current mail receptacle were changed to a locked cluster box. This is another potential area 

for additional research.

Conclusions and Suggestions

Results of this survey indicate that self-reported customer engagement with advertising mail varies with mode of delivery. Door 

delivery customers report a higher level of engagement with advertising mail than customers who received their mail through a 

neighborhood cluster box. Differences in engagement between curb delivery customers and cluster box customers are similar, but 

less pronounced. 

The results of this survey do not diminish the importance of centralized delivery to Postal Service cost savings efforts. We do 

suggest, however, that the Postal Service step up its customer research in this area. Part of that effort should be engagement 

with advertising mailers, especially those advertising mailers who stand to be most adversely affected by conversion of delivery to 

cluster boxes. More information would help them make more informed decisions about whom to target when designing their direct 

mail advertising campaigns. 

Finally, it should be noted that we examined mode of delivery’s impact(s) on advertising mail in broad terms. It could be the case 

that certain types or locations of cluster boxes might mitigate some of the adverse behaviors we discovered. More research is 

needed. Both the Postal Service and advertising mailers would benefit from having additional data on modes of delivery as soon 

as possible.

6

Modes of Delivery and Customer Engagement 

with Advertising Mail

Report Number RARC-WP-15-009
Detailed Analysis

Responsiveness to Advertising Mail by Delivery Mode

Professor Michael D. Bradley

Department of Economics

George Washington University

April 20, 2015

Modes of Delivery and Customer Engagement 

with Advertising Mail

Report Number RARC-WP-15-009 7
A. Introduction

Could the type of mail receptacle used by the U.S. Postal Service (the Postal Service) 

influence the ways in which postal customers interact with advertising mail? As the 

Postal Service contemplates a move to more cluster box deliveries, it is of value to 

examine this and other questions related to delivery mode. Specifically, do cluster box 

recipients differ from door or curb recipients in the way they handle and interact with 

advertising mail? Moreover, if cluster box recipients are observed to have different 

interactions, are they due to variations in the mail receptacle or to other factors – e.g.,

demographic or other differences?

This paper investigates these questions. It analyzes survey data, including data from a 

new survey commissioned by the Office of the Inspector General (OIG) to see if there is 

any evidence that cluster box recipients report different advertising mail retention or 

discard rates than door recipients or curb recipients. It also includes statistical analyses 

of data from two previous surveys conducted by the Postal Service.

Analysis of these three data sources indicates that cluster box recipients are less 

responsive to advertising mail than door recipients. The paper also investigates

possible reasons, other than receptacle type, that could explain why cluster box 

recipients appear less interested in advertising mail and reported lower advertising 

mail response rates.

Because it is based upon survey data, the following analysis describes what people 

said, not what they necessarily did. It thus focuses on their perceptions and attitudes 

about advertising mail not their actual handling and responses to the mail. In addition, 

the analysis identifies patterns and statistical differences in the survey responses, but 

does not investigate causality. The results should be interpreted with this in mind.

B. The OIG - InfoTrends Survey

1. Survey Design

To obtain data needed for investigating variations of responsiveness to advertising mail 

by delivery mode, the OIG worked with InfoTrends, Inc. to structure and conduct a 

survey designed to gather insight on the impact of cluster box usage on consumers’

behavior with respect to advertising mail.

1 (Different types of advertising mail, including 

nonprofit solicitation mail, are discussed in more detail in Section C2.)

 1 The OIG–InfoTrends survey concentrated on advertising mail, but asked questions about other types of 

mail as well. This study is limited to the data related to advertising mail.

8

Modes of Delivery and Customer Engagement 

with Advertising Mail

Report Number RARC-WP-15-009
The survey asked a group of mail recipients 20 to 25 questions, with two main purposes. 

a.)The survey was designed to produce data useful for gaining an understanding of 

how postal customers feel about cluster boxes and if/how those receptacles affect 

their interactions with advertising mail. In order to do this, the survey investigated 

how consumers handled, opened, read, and discarded a wide variety of advertising 

mail. These questions were asked of mail recipients with different types of mail 

receptacles making it possible to investigate different patterns of advertising mail 

interactions by mode of delivery. 

b.)The survey included a series of background questions about the participants. 

Response data can be used to check if any reported differences in mail interaction 

behavior can be attributed to factors other than mail receptacle type.

The OIG-InfoTrends survey was conducted in August 2014; and included 4,500 web-based

responses and 500 phone-based responses for consumers who do not have Internet 

access. The 5,000 total responses provided the primary data used in the analysis of 

mail recipients. 

2. Responses by Current Delivery Mode

The following chart displays the breakout of responses across current modes of 

delivery. It shows that 39 percent of respondents are in households with either a door 

slot or a mailbox near the door. Together, these categories comprise the “door” group 

and account for the largest group of total respondents by mode of delivery.

2

 

 

2 Of the 1,849 respondents classified as door recipients, 360 or 19.5 percent have a door slot, while the 

remaining respondents have a mailbox near the door. OIG-InfoTrends survey proportions presented in 

this chart are based on just the households receiving mail delivery and thus exclude a small proportion 

(about 4 percent) of respondents who picked up their mail at a post office or mailing center.

39%

32%

17%

12%

Distribution of Responses by 

Delivery Mode

Door Curb Central Cluster Box

9

Modes of Delivery and Customer Engagement 

with Advertising Mail

Report Number RARC-WP-15-009
To provide some perspective on this distribution, these proportions derived from survey 

responses can be compared with the proportions of delivery points, by type, reported

by the Postal Service for FY2013. The next table shows that for the Postal Service, curb 

delivery comprises the largest proportion of deliveries. This contrasts with the 

OIG-InfoTrends sample which shows more door deliveries than curb deliveries. The 

proportion of cluster box and central delivery points is about the same.3

Note that the central and cluster box categories from the Infotrends data are combined 

into one category for this comparison because that is the way the Postal Service 

delivery points data were presented.4 For the purposes of this paper, the differences 

in mode proportions are not critical because there are sufficient responses within each 

mode and the OIG-InfoTrends survey was designed to be representative of the U.S. 

population, not to replicate the Postal Service’s network as currently configured.

3. Profile of Participants 

The OIG-InfoTrends survey was sent to a general population sample and monitored by 

recipient age, gender, and region. The monitoring was done to ensure a match to the 

relevant proportions in the U.S. Census.

Before examining whether there is any evidence that cluster box recipients have 

different attitudes toward their advertising mail or handle their mail in a way that is 

different from other types of recipients, we need to check the demographic profiles of 

recipients to see if they exhibit material differences across receptacle types. If so, then it 

may be necessary to control for those differences when comparing cluster box 

recipients to other types of recipients.

The following table provides the overall mean (average) values and the means 

(averages) by receptacle type for important demographic variables such as age, 

income, and education.

 3 Central delivery boxes are banks of mailboxes in apartment buildings, condominiums, etc. 4 See, United States Government Accountability Office, “U.S. Postal Service: Delivery Mode Conversions 

Could Yield Large Savings, but More Current Data are Needed,” May 2014, p. 6.

10

Modes of Delivery and Customer Engagement 

with Advertising Mail

Report Number RARC-WP-15-009
In all instances, the average values for cluster box recipients were quite close to the 

full sample averages, suggesting that there is nothing atypical about their demographic

profiles. In addition, the demographics for cluster box recipients differed little from the 

demographics for door and curb recipients. This observation is important when 

comparing how these different types of mail recipients handle their mail; it suggests that 

any differences in attitudes towards their advertising mail cannot be attributed to the 

demographic factors of age, education, income, or employment.

5

One area in which there was a marked difference between door recipients and cluster 

box recipients was in the distribution by gender. Respondents with door receptacles 

were 54 percent male, whereas cluster box respondents were only 45 percent male.

These differences were large enough to merit further analysis in evaluation of survey

results. Curb respondents had a gender distribution that was quite similar to the gender 

profile for cluster box recipients.

 

5 For expositional convenience, we will define mail recipients by the type of receptacle in which they 

receive their mail. Thus, the term “curb recipient,” refers to those households who receive their mail in a 

curb line box.

51.7%

45.2% 46.5%

54.0%

48.3%

54.8% 53.5%

46.0%

0.0%

10.0%

20.0%

30.0%

40.0%

50.0%

60.0%

Central Cluster Box Curb Door

Gender Distribution of Respondents By Delivery 

Mode

Male Female

11

Modes of Delivery and Customer Engagement 

with Advertising Mail

Report Number RARC-WP-15-009
The potential impacts (or lack of potential impacts) of gender distribution are discussed 

in Section E2. 

One other area of difference between door recipients and cluster box recipients relates 

to their relative Internet access at home. Door recipients reported a much lower rate of 

Internet access than the other type of recipients. This also could have an impact on 

comparisons of door recipients to other types of recipients and bears investigation when 

further evaluating survey results. 

The potential impacts of differences in Internet access are discussed in Section E3. 

Responses by population density and by residential type are discussed and investigated 

in Section E4. 

C. Cluster Box Recipients’ Interactions with Advertising Mail Are Different

1. General Observations

The OIG-InfoTrends survey produced evidence indicating that cluster box recipients are 

less closely connected to advertising mail than door recipients. The differences were

found to be statistically significant after a series of statistical tests, detailed below. 

One set of evidence relates to how recipients view cluster boxes. For example, cluster 

box recipients found their mailbox location to be less convenient than door or even curb 

recipients. Nevertheless, over 80 percent of cluster box recipients stated that they found 

their mailbox location to be convenient.

91.2%

96.7% 97.0%

76.8%

0.0%

10.0%

20.0%

30.0%

40.0%

50.0%

60.0%

70.0%

80.0%

90.0%

100.0%

Central Cluster Box Curb Door

Percentage of Respondents with Internet 

Access

12

Modes of Delivery and Customer Engagement 

with Advertising Mail

Report Number RARC-WP-15-009
Perhaps more importantly, the survey found that among the recipients that did not 

already have a cluster box, over 60 percent would be displeased if their mail receptacle 

were changed to a locked cluster box. See figure below.

95.5%

90.2% 87.2%

80.8%

25

35

45

55

65

75

85

95

105

Door Curb Central Cluster Box

% Saying it is Convenient

Percentage of Respondents Who Find the 

Location 

of Their Mailbox to Be Convenient

13

Modes of Delivery and Customer Engagement 

with Advertising Mail

Report Number RARC-WP-15-009
2. Observations by Type of Advertising Mail 

A second set of evidence relates to the attention that different types of mail recipients 

gave to the advertising mail they received. The OIG-InfoTrends survey asked survey 

participants to report how they handled different types of advertising mail. Participants

were asked to choose one of the following answers that described how they handled 

their advertising mail by type of mail piece:

1. Read and respond to the mail6

2. Read and throw away the mail

3. Set the mail aside for later use

4. Throw away the mail without reading it.

The OIG-InfoTrends survey examined many different types of advertising mail to see 

how interactions with that mail varied by type. Participants were asked which action they

took for the following seven types of advertising mail:

1. Advertising mail from local companies I do business with

2. Advertising mail from national companies I do business with

3. Advertising mail from companies I do not do business with

4. Donation solicitations

5. Credit card solicitations

6. Catalogs

7. Mail that includes a coupon.

 6 These are the percentages of respondents who said they would read and respond to a particular 

advertising mail piece. Actual response rates are likely to be lower.

14

Modes of Delivery and Customer Engagement 

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Report Number RARC-WP-15-009
The results indicated that different types of advertising mail were handled in different 

ways by all recipients.7 Credit card solicitations were most likely to be thrown away

without being read. Charitable solicitations were also discarded at a high rate, but not as 

high as credit card solicitations. Both catalogs and advertising mail from companies with 

which the recipient has done business had relatively high read and respond rates.

Finally, mail with coupons included generated high response rates across-the-board.

Of particular interest, the OIG-InfoTrends survey produced data on how the read and 

respond rates for advertising mail varied across groups of participants defined by their 

type of mail receptacle. Comparing these rates provides some insight into whether or 

not the mail receptacle might affect how recipients interact with their advertising mail.

First, the OIG-InfoTrends data were used to compare the read and respond rates, 

as well as the discard rates, for mail recipients with cluster boxes with the read and 

respond rates and discard rates for mail recipients who received door delivery. The next 

set of figures graphically displays the results of this comparison.

The figure below shows the read and discard rates for catalogs. The catalog read and 

respond rate for door recipients, at 11.6 percent, was twice the read and respond rate 

for cluster box recipients, at just 5.5 percent. In contrast, 17.1 percent of cluster box 

recipients threw away their catalogs without looking at them but just 12.5 of door 

recipients did so. These results suggest that cluster box recipients were less receptive 

to catalogs then were door recipients.

 7 Note that the sum of the read and respond rate and the discard without reading rate for any type of 

advertising mail is less than 100 percent for each delivery mode. This is because survey participants also 

provided “read and throw away” and “set aside for later” responses. Because the implications of these 

responses for advertising mail engagement are less clear, our initial analysis of the survey data focused 

just on the read and respond and discard rates. Future research may be able to glean additional insights 

from the intermediate categories.

15

Modes of Delivery and Customer Engagement 

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Report Number RARC-WP-15-009
Next, we investigated advertising from companies with which the mail recipient has 

already done business, including both local companies and national companies. Both 

cluster box recipients and door recipients were more receptive to this type of mail than 

they were to catalogs, as the read and respond rates were higher than for catalogs. But 

again, both graphs display the pattern that door recipients had higher read and respond

rates and lower discard rates.

0

2

4

6

8

10

12

14

16

18

Read & Respond

Toss Without Reading

Percentage of Responses

Catalogs

Door Cluster Box

0

5

10

15

20

Read & Respond

Toss Without Reading

Percentage of Responses

Advertising Mail from National Companies 

I Do Business With

Door Cluster Box

16

Modes of Delivery and Customer Engagement 

with Advertising Mail

Report Number RARC-WP-15-009
As should be expected, the read and respond rates were much lower, and the discard 

rates were much higher, for advertising mail from companies with which the recipient 

had not done business, regardless of receptacle type. However, this difference in 

overall rates did not change the relative pattern exhibited by other types of advertising 

mail. Door recipients exhibited higher read and respond rates and lower discard rates

than cluster box recipients. 

0

5

10

15

20

25

Read & Respond

Toss Without Reading

Percentage of Responses

Advertising Mail from Local Companies 

I Do Business With

Door Cluster Box

17

Modes of Delivery and Customer Engagement 

with Advertising Mail

Report Number RARC-WP-15-009
0

10

20

30

40

50

Read & Respond

Toss Without Reading

Percentage of Responses

Advertising Mail from Companies 

I Do Not Do Business With

Door Cluster Box

05

10

15

20

25

30

35

40

Read & Respond

Toss Without Reading

Percentage of Responses

Donation Solicitations

Door Cluster Box

18

Modes of Delivery and Customer Engagement 

with Advertising Mail

Report Number RARC-WP-15-009
Credit card and non-profit solicitations generated similar patterns of interaction, albeit 

with recipients less likely to interact with credit card solicitations. Just 10.6 percent of 

door recipients and 3.1 percent of cluster box recipients read and responded to credit

card solicitations. At the same time, 40.2 percent of door recipients and 59.5 percent of 

cluster box recipients discarded credit card solicitations without looking at them. 

The last type of mail covered in the survey was advertising mail that included a coupon.

The next figure shows that coupon mail also had higher read and respond rates for door 

recipients, so all seven types of advertising mail have this characteristic. But, unlike the 

other six types of mail in which the discard rates were higher for cluster box recipients, 

the discard rate for coupon mail was the same for cluster box and door recipients.

0

10

20

30

40

50

60

Read & Respond

Toss Without Reading

Percentage of Responses

Credit Card Solicitations

Door Cluster Box

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These results suggest that cluster box recipients were less responsive than door 

recipients to the ad mail they received, but statistical evidence on these differences is 

helpful in assessing the validity of this comparison. This requires formal testing as to 

whether there is a difference between the responsiveness of cluster box recipients and 

the responsiveness of door recipients. By testing differences in both the “read and 

respond” proportions and the “throw out without reading” proportions, we can determine 

that the observed differences are statistically significant. 

3. Hypothesis Testing

a. Cluster Box and Door Read and Respond Rates

The statistical testing starts with the assumption that the groups of door and curb 

recipients are independent samples for basis of calculating the proportions of mail read 

and responded to. (This is typically the case in surveys, unless the subset respondents

are matched.8

) The next step is to label the outcome that a piece of mail is “read and 

responded to” by a door recipient as a “success” and define pp1 as the probability of a 

success (a mail piece is read and responded to) for door delivery recipients. 

Quantitatively, pp1 is measured as the ratio of pieces read and responded to relative to 

 

8 For respondents to be matched, they either have to be the same people in both groups, or people 

who have been individually matched on an important characteristic that might potentially influence the 

outcome. For example, matching would occur if both cluster box and door recipients were restricted to be 

women between the ages of 45 and 60. That is not the case in the InfoTrends survey. Door recipients and 

cluster box recipients are two completely different groups of individuals that we want to compare to 

determine if they are significantly different from one another with regard to their interaction with 

advertising mail.

0

5

10

15

20

25

Read & Respond

Toss Without Reading

Percentage of Responses

Mail that Includes a Coupon

Door Cluster Box

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all pieces handled by door recipients. The next step is to define pp2 as the probability of 

success for cluster box recipients and measured by the proportion of pieces read and 

responded to by cluster box recipients. The observed success rates in the two samples, 

pp̂

1 and pp̂2 are the estimates of their corresponding population success rates. The null 

hypothesis to be tested is that pp1 = pp2, or that pp1 − pp2 = 0. Note that under this null 

hypothesis, proportions of mail pieces read and responded to are the same for both 

door and cluster box recipients, so one can pool the information across the two samples 

to obtain a common population proportion of success, ppcc. That common probability of 

success is given by:

pp̂

cc = nn1pp̂

1 + nn2pp̂2

nn1 + nn2

With this definition in place, one can form the test statistic required for testing the null 

hypothesis of an equal proportion of mail read and responded to for door and cluster 

box recipients as:

TTTTTTTT SSTTSSTTSSTTTTSSSS = pp̂

1 − pp̂2

�pp̂

cc (1 − pp̂cc) � 1

nn1

+ 1

nn2

�

Computing this test statistic permits testing the hypotheses of equal read and respond 

rates. The critical value at a 95 percent level of confidence is 1.96, and the critical value 

at a 90 percent level of confidence is 1.65.9 This means the null hypothesis of equal 

responsiveness between door and cluster box recipients is rejected if the calculated test 

statistic is greater than either of these values.

The table below presents the hypothesis tests for the seven types of advertising mail

included in the survey. It shows that for all seven types of mail, the read and respond 

rate for cluster box recipients was smaller, and sometimes greatly smaller, than for door 

recipients. For “advertising mail from national companies with which the recipient does 

business,” the read and respond rate for cluster box recipients was half of what it was 

for door recipients and for “donation solicitations” the cluster box recipient rate was 

about one-third of the door recipient response rate. Moreover, all of the test statistics 

 9 Two-tailed tests are used when investigating the various hypothesis surrounding cluster box recipients 

and door (or other mode) recipients. In a two-tailed test the null hypothesis of equality between two 

values is compared to an alternative hypothesis that the two values are not equal, without restriction 

about which one of the two values is greater. In a one-tailed test, the null hypothesis of equality between 

the two values, is compared to an alternative is that one of the values is greater (or lesser) than the other. 

For a given level of significance, it is harder to reject the null hypothesis with a two-tailed test than it is 

with a one-tailed test, so the application of two-tailed tests is a conservative approach. 

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are well above 1.96, indicating that there is little chance that these results are simply 

due to statistical fluctuation.

b. Cluster Box and Door Discard Rates

The previous results indicate that cluster box recipients were less responsive to 

advertising mailings than door recipients, in terms of their positive responses to those 

mailings. However, it is also possible to test for differences in mail recipients’ negative 

responses to ad mailings. As discussed above, the OIG-InfoTrends survey also 

measured the proportion of participants that threw out their advertising mail without 

reading it. The statistical tests used to examine read and respond rates can also be 

used to see if cluster box recipients’ discard rates were the same as for door recipients.

As before, the null hypothesis is that discard rates are the same across receptacle types 

and the absolute critical values are the same. The one difference is that negative values 

for the calculated test statistics mean that the cluster box discard rate is greater than 

door discard rate. This means that the associated critical values will be negative at

-1.65 and -1.96.

The next table presents the results of testing this hypothesis for the seven mail 

categories. The results are not as uniform in rejecting the null hypothesis as for the read 

and respond tests, but they do indicate that cluster box recipients generally had higher 

discard rates than door recipients.

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In all cases, the discard rate was higher for cluster box recipients than for door 

recipients, and the null hypothesis of an equal discard rate for door and cluster box 

recipients is rejected for five of the seven mail types. Only two categories, “advertising

mail from local companies with which the recipient does business” and “mail that 

includes a coupon,” had statistically similar discard rates. In some cases, the difference 

in the discard rates was large. Door recipients discarded 40 percent of their credit card 

solicitations without looking at them while cluster box recipients discarded 60 percent.

Similarly, door recipients immediately discarded about 32 percent of “advertising mail 

from companies with which they do not do business,” whereas cluster box recipients 

immediately discarded 46 percent of that mail.

c. Cluster Box and Curb Recipients

Comparison of cluster box recipients with door recipients produced consistent evidence 

that door recipients were more engaged with advertising mail. The same methods can 

be used to examine possible differences between cluster box recipients and curb 

recipients. The next page presents the set of graphs comparing read and respond and 

discard rates for curb recipients and cluster box recipients. The graphs reveal far fewer

differences between curb and cluster box recipients than there were for door and cluster 

box recipients. 

Mode Sample 

Proportion

Test 

Statistic Result

Cluster Box 13.2%

Door 12.3% -0.55 Do not reject

Known Local Business

Tests of the Hypotheses that the Do Not Read and Discard Rate for Cluster Box 

Recipients Is the Same as for Door Recipients

Mode Sample 

Proportion

Test 

Statistic Result

Cluster Box 14.5%

Door 11.3% -2.08 Reject at 95%

Known National Business

Mode Sample 

Proportion

Test 

Statistic Result

Cluster Box 59.5%

Door 40.2% -8.14 Reject at 95%

Credit Card Solicitations

Mode Sample 

Proportion

Test 

Statistic Result

Cluster Box 46.4%

Door 31.6% -6.47 Reject at 95%

Unknown Business

Mode Sample 

Proportion

Test 

Statistic Result

Cluster Box 6.1%

Door 6.0% -0.10 Do not reject

Mail that Includes a Coupon

Mode Sample 

Proportion

Test 

Statistic Result

Cluster Box 40.0%

Door 31.2% -3.93 Reject at 95%

Donation Solicitations

Mode Sample 

Proportion

Test 

Statistic Result

Cluster Box 17.1%

Door 12.5% -2.84 Reject at 95%

Catalogs

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0

2

4

6

8

10

12

14

16

Read & Respond

Toss Without Reading

Percentage of Responses

Advertising Mail from National Companies 

I Do Business With

Curb Cluster Box

0

2

4

6

8

10

12

14

Read & Respond

Toss Without Reading

Percentage of Responses

Advertising Mail from Local Companies 

I Do Business With

Curb Cluster Box

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05

10

15

20

25

30

35

40

45

50

Read & Respond

Toss Without Reading

Percentage of Responses

Advertising Mail from Companies 

I Do Not Do Business With

Curb Cluster Box

05

10

15

20

25

30

35

40

45

Read & Respond

Toss Without Reading

Percentage of Responses

Donation Solicitations

Curb Cluster Box

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0

10

20

30

40

50

60

70

Read & Respond

Toss Without Reading

Percentage of Responses

Credit Card Solicitations

Curb Cluster Box

02468

10

12

14

16

18

Read & Respond

Toss Without Reading

Percentage of Responses

Catalogs

Curb Cluster Box

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While the read and respond rates were slightly larger for curb recipients than cluster box 

recipients, the differences were quite small. Similarly, discard rates were very similar 

across people receiving mail in these two types of receptacles. 

d. Cluster Box and Curb Tests

This similarity is highlighted by results of statistical tests. The next set of tables contains 

the results of testing the hypotheses that the read and respond rates were the same for 

cluster box and curb recipients for the seven types of advertising mail. In no instance 

can this hypothesis be rejected at the 95 percent level, and only twice can it be rejected 

at the 90 percent level.10 This suggests a strong similarity between the read and 

respond rates for the two types of recipients.

 

10 If a one-tailed test was performed, two of the hypotheses could be rejected at the 95 percent level.

0

2

4

6

8

10

12

14

16

18

Read & Respond

Toss Without Reading

Percentage of Responses

Mail that Includes a Coupon 

Curb Cluster Box

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Testing discard rates also reinforces the similarity in the way that cluster box and curb 

recipients interact with advertising mail. In only one case, catalogs, was the hypothesis 

of equal discard rates rejected.

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D. Evidence from Other Surveys

1. Alternative Sources of Data

In order to evaluate the results from the OIG-InfoTrends survey, the OIG also obtained 

relevant data from two recent Postal Service surveys: the Mail Moment survey and the 

Recruitment Questionnaire of the Household Diary Study. The Mail Moment survey was 

conducted by InnoMedia in 2012. It had 1,078 participants and was designed to foster 

understanding of the value of the consumer’s daily “mail moment.” That is, the Mail 

Moment survey was designed to investigate the value that households receive from

different kinds of commercial and advertising mail.

The Recruitment Questionnaire of the Household Diary Study is part of an ongoing 

study of mailing behavior by the Postal Service. The version of the Recruitment 

Questionnaire used in this analysis was taken in 2013-2014 and had 4,549 participants.

While much of the Household Diary Study analysis focuses on the quantities of mail 

sent and received by households, the Recruitment Questionnaire elicits a variety of 

attitudinal and demographic information from diary study participants.

Mode Sample 

Proportion

Test 

Statistic Result

Cluster Box 13.2%

Curb 12.1% -0.68 Do not reject

Known Local Business

Tests of the Hypotheses that the Do Not Read and Discard Rate for Cluster Box 

Recipients Is the Same as for Curb Recipients

Mode Sample 

Proportion

Test 

Statistic Result

Cluster Box 14.5%

Curb 13.8% -0.47 Do not reject

Known National Business

Mode Sample 

Proportion

Test 

Statistic Result

Cluster Box 59.5%

Curb 60.5% 0.40 Do not reject

Credit Card Solicitations

Mode Sample 

Proportion

Test 

Statistic Result

Cluster Box 46.4%

Curb 46.3% -0.04 Do not reject

Unknown Business

Mode Sample 

Proportion

Test 

Statistic Result

Cluster Box 6.1%

Curb 5.0% -0.80 Do not reject

Mail that Includes a Coupon

Mode Sample 

Proportion

Test 

Statistic Result

Cluster Box 40.0%

Curb 41.8% 0.82 Do not reject

Donation Solicitations

Mode Sample 

Proportion

Test 

Statistic Result

Cluster Box 17.1%

Curb 13.6% -2.30 Reject at 95%

Catalogs

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Although these two postal surveys were not specifically designed for cluster box 

research and asked different questions from the OIG-InfoTrends survey, they 

both generated data that can be used to potentially corroborate or contradict the 

OIG-InfoTrends results. These data are discussed below.

a. Mail Moment Survey

The Mail Moment survey data support the inference that cluster box recipients have 

lower retention rates and higher discard rates than either door or curb recipients. The 

Mail Moment survey asked several questions that can contribute to an investigation of 

different interactions with advertising mail for cluster box recipients than for door or curb 

recipients. For example, one question in the Mail Moment survey elicited participants’ 

interest in picking up their mail at the first opportunity. As the next table shows, cluster 

box recipients were far less likely to pick up their mail at the first opportunity then were 

either door or curb recipients. This suggests that cluster box recipients were less 

engaged with their mail than other types of recipients.

Another question in the Mail Moment survey asked participants to identify what they did 

with the advertising mail, catalogs, and flyers they received. The choices included keeping

the mail, discarding the mail without reading it, or reading the mail and then discarding it.

The next table presents both the retention rate and the discard-without-reading rate for 

door, curb, and cluster box recipients. The table shows that cluster box recipients had

the lowest retention rate and the highest discard-without-reading rate.

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Using the statistical procedure described in the previous section, it is possible to test 

whether the retention rate for cluster box recipients was significantly less than for door 

recipients or curb recipients. It also possible to test if the cluster box recipient discard 

rate was significantly greater than for door or curb recipients. The next table presents 

the calculated test statistics for those tests. (Recall that a positive calculated test 

statistic implies the cluster box rate is smaller and a negative calculated tests statistic 

implies that the cluster box rate is larger.)

If the calculated test statistic is larger (in absolute value) than the critical value of 

1.96 then the hypothesis of equal retention or discard rates can be rejected at the 

95 percent level.11 In all cases, the null hypothesis is rejected. 

Thus, the Mail Moment survey data support the inference that cluster box recipients 

have lower retention rates and higher discard rates that either door or curb recipients.

These are consistent with the Infotrends’ result for door and cluster box recipients, but 

unlike the OIG-Infotrends’ result, they found that curb and cluster box recipients had 

similar retention and discard rates. 

 11 This level of significance is for a two-tailed tests. A critical value of just 1.65 needs to be exceeded to 

reject the null under a one-tailed test.

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b. Household Diary Recruitment Questionnaire

One important question in the Household Diary Study Recruitment Questionnaire was 

geared to how recipients responded to advertising mailings. It asked participants to 

indicate how much attention members of the household pay to advertising material 

received through the mail. The options are: (1) "usually read it," (2) "usually scan it," 

(3) "read some but don't read others," and (4) "usually don't read it." The following table 

lists the proportions of recipients, by receptacle type, that reported usually reading their 

advertising mail.

The table shows that "usually read it" proportion for cluster box recipients is well below 

the proportions for the other receptacle types, and it would be of interest to test the null 

hypothesis that the "usually read it" proportion was the same for cluster box recipients 

as it was for door and curb recipients.

Using the procedure described in the previous section, these hypotheses were tested 

and the results appear in the next table. The results indicate rejection of the null 

hypothesis of equal reading rates at the 95 percent level of significance for door 

recipient and the 90 percent level of significance for the curb recipients.12

In other words, the Household Diary data indicated that cluster box recipients had a 

significantly lower advertising mail read rate than door and curb recipients. This 

matches the OIG-Infotrends results showing similar differences between cluster box and 

door recipients but shows more differences for cluster box and curb recipients than the 

Infotrends’ results.

 12 Using a one-tailed test, both null hypotheses could be rejected at the 95 percent level of significance.

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2. Summary of Investigation of Alternative Sources

The data from the two Postal Service surveys of mail recipients corroborates the main 

result found in the OIG-InfoTrends survey: cluster box recipients are less likely to read 

and retain their advertising mail than door recipients. The OIG-Infotrends’ data showed 

little difference between cluster box and curb read and respond rates, but data from the 

two Postal Service surveys indicated that cluster box recipients had lower read and 

response rates than did curb recipients. Finally, the Postal Service surveys produced 

evidence that cluster box recipients were more likely to discard their advertising mail 

without reading it than were either door or curb recipients.

E. Exploring Other Possible Reasons for the Results

The evidence from the OIG-InfoTrends survey indicates a different pattern of 

interactions with advertising mail for those who receive advertising mail in cluster boxes 

rather than in other types of mail receptacles. However, further investigation is 

warranted to be sure that these observed differences are due to the difference in mail 

receptacle and not due to an underlying variable, such as attitude toward advertising 

mail, household age, household income, population density, type of residence, gender, 

or Internet use.

It is also important to note that this investigation is limited to survey data examining 

postal customers’ attitudes and self-reported actions. These analyses are not intended 

to investigate causality. As detailed below, the survey design and analyses controlled

for other factors, but we have not constructed a causal model of cluster box recipients’ 

interactions with advertising mail and do not claim to have done so.

1. General Attitudes Towards Advertising Mail 

One possible reason for the differences in advertising mail responsiveness is that 

cluster box recipients, apart from the way in which they receive their mail, simply do not 

like advertising mail. That is, if people who do not like advertising mail just happen to 

receive their mail in cluster boxes, it could explain part or all of the differences in 

response rate between door recipients and cluster box recipients. To investigate this 

hypothesis, an analysis was performed on an OIG-InfoTrends survey question that 

asked the participants to indicate how they feel about the advertising mail they receive.

Participants were asked to rate their view of advertising mail on a scale from strongly 

liking it to strongly disliking it.

The following chart presents the results for door, curb, and cluster box recipients. It 

plots the percentages for each answer. Very few people strongly like their advertising 

mail and relatively few people strongly dislike it. More importantly, the general pattern is 

the same for all three receptacle types. It appears that there may be a somewhat more 

positive attitude by door recipients, as they have slightly higher approval rates and 

slightly lower disapproval rates when compared to cluster box recipients.

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The possible differences can be quantified by forming an index of advertising mail 

appeal. If we assign each of the categories a numerical value, ranging from a “1” for 

strongly liking to a “5” for strongly disliking, we can compute an index value. We do so 

by multiplying each answer’s proportion by its numerical value and finding the sum. The 

next table presents the calculated index values for the different receptacle types. As 

expected, door recipients have the lowest value, indicating the strongest preference for 

advertising mail, but the differences are quite small and would not appear to be 

sufficient to explain the significantly lower read and respond rates for curb recipients.13

As a result, we will investigate other possible reasons for the differences.

 

13 In fact, these differences could be caused by the inconvenience cluster box recipients face when 

disposing of any unwanted advertising mail. This factor could also explain why the index value for curb 

recipient is higher than for door recipients. 

0

5

10

15

20

25

30

35

40

45

Strongly like Somewhat like Indifferent Somewhat dislike Strongly dislike

% Naming Each Answer

Attitudes Toward Advertising Mail Received

Door Curb Cluster Box

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As indicated in Section C, the average values for key demographics, including age, 

income, and education are quite similar for door and cluster box recipients, ruling out 

these variables as potential causes for different response rates. But there were two 

types of demographics that were different between cluster box recipients and door 

recipients: gender and Internet access. Next, we investigate these as potential alternative 

explanations for the apparent differences between door and cluster box recipients.

2. Responses by Gender

First, we examine the differential in gender proportions. (Recall that door delivery 

recipients were about 54 percent male, while cluster box recipients were about 

55 percent female.) If the responsiveness to advertising mail is different for men and 

women, then this difference in gender profile could be the underlying cause for the 

measured differences between door recipients and cluster box recipients. Investigating 

this issue requires splitting the OIG-InfoTrends dataset into a male subset and a female 

subset.14 There were 2,512 female respondents (50.2%) and 2,488 male respondents 

(49.8%).15

The statistical analysis that was performed on the full set of data is repeated separately 

for the male and female subsets. The results will identify if men and women have 

different patterns in their responsiveness to the advertising mailings they receive.

The next table presents the results of testing the differences between door recipient 

advertising mail responsiveness and cluster box recipient advertising mail 

responsiveness, by gender. The first two columns test the differences in read and 

respond rates across the seven mail categories. As with the overall results, in all cases, 

the hypothesis of equal response rates was rejected in favor of the inference that the 

door read and respond rate is higher than the cluster box read and respond rate.

 14 There were 2,512 female respondents (50.2%) and 2,488 male respondents (49.8%). 15 As discussed above, the web survey was sent out to a general population sample that was monitored 

for age, gender and region. These areas had quotas to match the U.S. census. The survey did not screen 

for head of household; it went to a general population sample. The question about how often the 

respondents pick up their mail is covered in Question 16 of the survey. 

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The table shows that this result holds for both men and women. The next two columns 

present the results of testing the “do not read and throw away” rates between door 

recipients and cluster box recipients for men and women.

Although they do not exactly replicate the full sample results, the results by gender 

generally match them. For the full sample, equivalence of discard rates was rejected for 

five of the seven mail categories. For the female subsample, the number of rejections 

rises to six out of seven, adding the “mail that includes a coupon” category to the list.

For men the number of rejections of equal discard rates falls to three of the seven.

Taken together, these results suggest that differences in gender profile are not the 

basis for differences in response and discard rates between door recipient and cluster 

box recipients.

3. Responses by Internet Access

Next, the possible role of differential Internet access is investigated. Nearly all 

cluster box respondents indicated they had Internet access (96.7%), while just over 

three-quarters of door respondents had Internet access (76.8%). As with gender, this 

raises the possibility that the observed difference in response rates between door and 

cluster box recipients may have to do with Internet access and not mail receptacle type.

To test this possibility, the analysis that was performed on the full set of data is repeated 

for just the 4,403 respondents that said they had Internet access. In other words, all of 

the door recipients and cluster box recipients included in this test reported having 

Internet access, so differential Internet access can be ruled out as a source of mail 

responsiveness differences.

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The next table provides the results of repeating the statistical tests for Internet users. As 

with the complete sample, the test for read respond rates showed that among Internet

users, the door response rate was greater than the cluster box response rate for all mail 

categories. This indicates that the differences between door and cluster box read and 

respond rates are not due to differential Internet access.

The test for discard rates provides even stronger evidence of differences between 

cluster box recipients and door recipients. When all responses were used, there were 

two categories, “advertising mail from companies with which I do business” and “mail 

that includes a coupon” for which we could not reject the null hypothesis of equal 

discard rates. Using the Internet access only subsample, the hypothesis for both of 

those categories is rejected at the 90 percent confidence level. In sum, there is no 

evidence that a difference in Internet access is the basis for the observed differences in 

advertising mail response between door recipients and cluster box recipients.

4. Responses by Population Density

One additional investigation was pursued in analyzing alternative sources of observed 

responsiveness rates. This investigation examines whether the differences between 

cluster box recipients and door recipients are the same in both rural (low population 

density) and urban (high population density) areas. For example, we can test whether 

cluster box recipients have lower read and respond rates in low population density 

areas than they do in high population density areas. 

This investigation required obtaining data by ZIP Code from the most recent (2010) 

Census. The Census data set contains information on 33,120 five-digit ZIP Codes 

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including the ZIP’s total population and square miles of land area. These variables can 

be used to construct a measure of population density – the number of people per 

square mile.

The next table shows the distribution of InfoTrends survey responses across population 

density quartiles:16

The table shows that the survey responses came primarily from the high density 

ZIP Codes, with almost 65 percent of them coming from highest density quartile. Also,

only 3 percent of the responses came from the lowest population density quartile. The 

concentration of responses in the two highest density quartiles makes it difficult to 

perform an analysis by population quartile because there are so few responses from low 

density areas. 

To have sufficient responses in the lower density areas, the OIG-InfoTrends data set 

will be split into two subsets, with the high population density subset consisting of 

responses from ZIP Codes in the highest density quartile and the low density subset

consisting of responses from ZIP Codes in the remaining three quartiles. Even with this 

split, just 35 percent of the responses (1,728) come from the lower density ZIP Codes.

Nevertheless, as the next table shows, there are material differences in population 

density across these two subsets.

 16 Although there were, 5000 responses in the survey, we were able to match 4,927 of them to the list 

of Census ZIP Codes. The remaining 73 could either be from ZIP Codes that were not in existence in 

2010 or from responses in which ZIP Code was erroneously reported.

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In addition, there are sufficient observations in the low density subset to support 

statistical testing of the differences between cluster box and door read and respond 

rates. The results of that testing, along with the same tests for discard rates, are 

presented in table below. For both population density subsets, the results for the read 

and respond rates exactly matched the overall results. The tests showed that for all 

categories of advertising mail, read and respond rates for door recipients were

significantly higher than read and respond rates for cluster box recipients. This 

difference held for both high and low density areas. As a result, lower read and respond 

rates for cluster box recipients do not appear to be arising because of differences in 

population density.

The results for the high density subset exactly matched the overall results for discard 

rates, with five of the seven ad mail categories showing statistically higher discard rates 

for cluster box recipients. The results for the low density subset were not as close. 

Although the results generally showed higher discard rates for cluster box recipients, 

as compared with door recipients, the difference was statistically significant for only 

two of the five advertising mail categories. Nevertheless, there is no evidence that 

population density is the explanation for difference in discard rates between door and 

cluster box recipients.

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Data from the two Postal Service surveys were also investigated to see if there were

any evidence of variables other than the mail receptacle causing the observed 

differences in interaction with advertising mail. (Recall that both the Mail Moment survey 

and the Household Diary Study survey produced evidence suggesting the cluster box 

recipients had a higher level of interaction with the Internet.)

In the Mail Moment survey, cluster box recipients appeared to have a higher affinity for 

Internet use. Cluster box recipients were less attached to the mail for paying bills than 

door recipients and they were less likely to worry about the safety of electronic 

payments. In the Household Diary Study survey cluster box recipients appeared to have 

slightly higher broad band Internet access and are less likely to have no Internet access

than door recipients.

The Household Diary Study survey suggests that this difference may also be reflected 

in cluster box households' attitudes about the security of the mail as compared to 

messages on the Internet. Just under 30 percent of cluster box recipients thought the 

mail was more secure and 60 percent thought the two were equally secure. In contrast, 

approximately 40 percent of door recipients thought the mail was more secure than the 

Internet, with about 50 percent thinking they were equally secure.

The two Postal Service surveys did not produce data that permitted testing the 

hypothesis as to whether a greater affinity of Internet use among cluster box recipients 

was the source of difference in responsiveness of cluster box recipients as compared to 

door recipients. But the OIG-InfoTrends survey data did support such an analysis;

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results of testing indicated that the differences remained, even when just comparing 

Internet users.

It is important to keep in mind that these results are based upon survey data, not the 

actions postal recipients performed. The results should thus be interpreted as reflecting 

peoples’ attitudes toward advertising mail, not their interactions with it. Finally, the 

results identify patterns and statistical differences, but do not investigate causality.

5. Responses by Residential Type

Finally, data from the Household Diary Study survey indicated that the type of residence 

in which the recipient lives did not appear to affect how cluster box recipients interact 

with advertising mail. A smaller proportion of cluster box recipients then door recipients 

read their advertising mail whether both groups lived in single detached houses, 

apartments and condominiums, or townhouses and duplexes.

F. Conclusion

As the Postal Service contemplates a move to more cluster box deliveries, an

important strategic question to investigate is whether the type of mail receptacle could 

influence the way in which postal customers interact with the advertising mail they 

receive. This paper has examined this issue using data from a new survey 

commissioned by the OIG and conducted by InfoTrends as well as two previous 

surveys managed by the Postal Service. All three surveys were designed to be 

representative of the U.S. population and stratified by key demographic elements.

Results from extensive data analyses indicate that cluster box recipients had

significantly lower read and respond rates than door recipients for all types of 

advertising mail. In a number of instances, the cluster box read and respond rates were 

half of those for door recipients. Cluster box recipients also had higher discard without 

reading rates than door recipients.

Analysis of data from two other surveys commissioned by the Postal Service 

corroborated the main results from the OIG-InfoTrends survey.

To verify that the lower read and respond rates for cluster box recipients were not due 

to another variable such as household age, income, type of residence, gender, 

population density, or Internet access, subsequent analyses with rigorous statistical 

testing were performed. In all cases, the evidence indicated that the reported 

differences in read and respond rates were not due to alternative demographic or 

attitudinal variables.

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Survey 

Questionnaire

Cluster Box for Postal Delivery Research

Technology Usage

Q1: Do you have Internet access at home?

 Yes

 No

Q2: How do you most often access the Internet?

 Personal computer

 Work computer

 Public computer (e.g., library)

 Smartphone

 Mobile tablet

 Other (please specify)

 I do not use the Internet

Demographic Questions

Q3: How old are you?

 Under 18 years (terminate)

 18 to 24 years

 25 to 34 years

 35 to 44 years

 45 to 54 years

 55 to 64 years

 65 years or older

Q4: What is your gender?

 Male

 Female

Q5: Which state do you live in?

Please choose from the dropdown menu.

Include “Do not live in the U.S.” and terminate on this response.

Q6: What is your 5 digit zip code?

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Q7: What is the highest level of education you have achieved?

 Did not graduate high school

 Graduated high school

 Attended college

 Graduated 2-year college

 Graduated 4-year college

 Post graduate

Q8: What is your annual household income?

 Less than $15,000

 $15,000 to $24,999

 $25,000 to $34,999

 $35,000 to $49,999

 $50,000 to $74,999

 $75,000 to $99,999

 $100,000 to $149,999

 $150,000 to $199,999

 $200,000 and over

 Prefer not to answer

Q9: What is your employment status?

 Employed full time (more than 30 hours)

 Employed part time (less than 30 hours)

 Unemployed (including full-time students)

 Retired

 Homemaker

 Other (please specify)

Q10: Is anyone in your household disabled?

 Yes, I am

 Yes, I am (along with others in the household)

 Yes, others in the household are

 No

Mail Preferences

Q11: Where do you normally receive your mail? 

 Door slot

 Mailbox installed on my porch or near my front door

 Curbside single (not part of a cluster or group of mailboxes)

 Central mailbox cluster inside an apartment, condominium or other building

 Central mailbox cluster in my neighborhood

 PO Box (USPS or private)

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Q12: Where do you normally receive your packages?

 At my door

 In my lobby unsecured

 My neighbor/building manager accepts for me

 In a parcel locker at my outside cluster box

 At the shippers office (UPS/USPS/ FedEx)

 Other

Q13: In a typical month, how many parcels/packages do you receive?

 0

 1

 2-4

 5-7

 8-10

 11-13

 14-16

 17-19

 20+

Q14: Do you find the location of your mailbox to be convenient?

 Yes

 No

Q15: Do you consider your mail to be safe in the location where it is delivered?

Letter mail

 Yes, very safe

 Yes, usually safe

 No, somewhat unsafe

 No, very unsafe

Parcels/packages

 Yes, very safe

 Yes, usually safe

 No, somewhat unsafe

 No, very unsafe

Q16: In a typical week, how often do you check your mail?

 Six times

 Five times

 Four times

 Three times

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 Twice

 Once

 I do not check my mail weekly

Q17: Do you change how often you check the mail depending on the season?

 Yes

 No

Q18: Would you (do you) find it useful to have a lock on your mailbox?

 Yes

 No

Q19: How do you receive the following types of communications?

Only by mail

Both by mail 

and 

electronically

Electronicall

y only N/A

Newspapers and 

magazines    

Bills and statements    

Personal mail (letters, 

postcards, greeting 

cards, 

announcements)

   

Q20: On average, how many of the following types of communications do you receive each 

month via physical mail?

0 1 2-4 5-7 8-

10

11-

13

14-

16

17-

19 20+

Newspapers and 

magazines

Personal mail (letters, 

postcards, greeting 

cards, announcements)

Catalogs and other 

advertising mail

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Q21: In a typical month, how many different bills and statements do you receive only by 

mail, both by mail and electronically, and electronically only?

0 1 2-4 5-7 8-10 11-

13

14-

16

17-

19 20+

Only by mail

Both by mail and 

electronically

Electronically only

Q22: In an average month, what portion of your bills do you pay by mail?

 All

 Most 

 Half

 Some

 None

Q23: What do you typically do when you receive the following types of mail?

Read and 

respond

Set aside 

for later 

use

Read and 

throw 

away

Throw 

away 

without 

reading

N/A

Advertising mail from 

local companies I do 

business with

Advertising mail from 

national companies I 

do business with

Advertising mail from 

companies I do not do 

business with

Donation solicitations

Credit card 

solicitations

Catalogues

Mail that includes a 

coupon

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Feelings Regarding the Postal Service

Q24: How do you feel about the advertising mail you receive?

 Strongly dislike

 Somewhat dislike

 Indifferent

 Somewhat like

 Strongly like

Q25: How would you rate the level of service that you currently receive from the Postal Service?

 Very unsatisfied

 Somewhat unsatisfied

 Indifferent

 Somewhat satisfied

 Very satisfied

Q26: Suppose your mail delivery was moved to a locked cluster box in a central outdoor 

location in your neighborhood/apartment complex, how would you react?

 Very displeased

 Somewhat displeased

 Indifferent

 Somewhat pleased

 Very pleased

Q27: Would you consider paying a yearly fee to retain home delivery?

 Yes 

 No

How much would you be willing to pay per year to retain home delivery?

 $5 or less

 $5 to $25

 $25 to $50

 $50 to $75

 $75 to $100

 $100 or more

Q28: How would having a cluster box change how frequently you checked your mail?

 I would check it less often

 I would check it more often

 It would not change my current habit

 I already have a cluster box

Q29: If you had to use one word to describe the Postal Service, what would it be?

________________________

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U.S. Postal Service Office of Inspector General

1735 N. Lynn Street

Arlington, VA 22209

Telephone: 703-248-2100

www.uspsoig.gov

For media inquiries, contact Agapi Doulaveris

Telephone: 703-248-2286

adoulaveris@uspsoig.gov

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