Reference Name: SAMP-GLOSSARY Page 1 of 6

Title: Glossary of Sampling Terms

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Disclaimer: The definitions for these terms apply to PDP operations and may be 

different than the definitions provided by other agencies/programs. 

Alternate Site—the back-up site from the State's list of active sites where the sample 

should be collected if it is not available at the Primary (scheduled) Site.

Chain of Custody—documentation (e.g., worksheets or logbooks) that records sample 

movement from selection of the sample, to receipt at the laboratory, to final disposal of 

the extract(s). This documentation allows for traceability of movement of each sample.

Cold-to-the-Touch—the temperature of the surface of an object that "feels" colder than 

one’s own body temperature

Cross-Contamination—the physical movement and transfer of chemical or illnesscausing agents from one person, object, or place to another

Delicate Commodity—a commodity that may easily be damaged or spoiled if not 

properly packaged (to prevent movement) and kept cool (at a refrigerated temperature) 

during transport to its respective laboratory. Strawberries and eggs are examples of 

delicate commodities.

Distribution Center—a warehouse facility that purchases and receives food products

from multiple vendors, stores the food products on its premises, then distributes the 

products to multiple stores within its specific chain, e.g., a Safeway distribution center 

will receive, store, and distribute food for all the individual Safeway retail stores within its 

geographic proximity.

Double/Triple Sampling—extra sampling during a specified period of time to make up 

for times (most likely, seasons) when certain commodities are unavailable and therefore 

are unable to be collected. Double or Triple Sampling must be approved by MPD and 

the laboratory receiving the samples before it is initiated.

Electronic Sample Information Form (e-SIF)—digital version of the Sample 

Information Form that is entered and submitted using the RDE e-SIF software on 

handheld/laptop/desktop computers.

Ethylene Gas (C2H4)—a natural hormone that is produced by all plant tissue. It acts as 

a ripening agent that helps fruit become colorful and tasty by accelerating leaf and flower 

senescence (the wilting, fading, and general decay of plant tissue). Most plants produce 

ethylene gas even after they are harvested. When storing or transporting different types 

of produce in the same container, it is crucial to consider whether a certain commodity is 

an ethylene producer or is ethylene sensitive. For this reason, it is best to select 

produce that is not overly ripe.
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Title: Glossary of Sampling Terms

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Ethylene Producing Commodity—many fruits such as apples, bananas, and tomatoes 

show a strong increase in ethylene levels at the late green or breaker stage. As a 

consequence of high ethylene, chlorophyll is degraded and other pigments are 

produced. This results in the typical color of the mature fruit peel. When fruits are stored 

in an enclosed area, ethylene that is released from ripening and mature fruits 

accumulates and stimulates late-ripening fruits to premature ripening ("One rotten apple 

can ruin the whole basket"). Activity of many maturation-related enzymes thus increases. 

Ethylene producers should not be stored or packaged with ethylene sensitive products

because they may cause premature ripening of some products and may ruin others.

Ethylene Sensitive Commodity—generally, unripe produce is sensitive to ethylene gas 

and will commence ripening if stored with ethylene-producing commodities. Fruit and 

vegetables vary in their degree of ethylene sensitivity.

Extranet—also known as AGNISX, MPD’s Extranet is a browser-based portal site that 

allows MPD employees and participating States to share, modify, and discuss 

information electronically with users within and outside of USDA. The public does not 

have access to MPD’s Extranet.

Fact Sheet—a one-page document prepared by the PDP Sampling Manager that 

summarizes sample collection and shipping criteria for a specific commodity. 

Information included in a Fact Sheet includes: acceptable and unacceptable products or 

varieties for collection, desired sample collection size or weight, packaging and shipping 

instructions, and optimum storage/shipping temperatures. Fact Sheets for current PDP 

commodities must be made available to all sample collectors and are posted on MPD’s 

Extranet site.

FTE—Acronym for Full Time Equivalent. One FTE is equal to 2087 man-hours per year.

Hermetically Sealed—a seal on a bag or container that makes its contents airtight. The 

means by which the bag is sealed is by fusion, gasketing, crimping, or equivalent means 

so that no gas or vapor can enter or escape.

Internal SOPs—Standard Operating Procedures (SOPs) created by each State 

Sampling Manager that provide specific details concerning how a procedure is to be 

implemented in his/her particular State. Internal SOPs are intended as a supplement to

PDP SOPs, which represent minimum PDP requirements and are presented as a 

general guideline.

Objective Selection/Judgment—a selection process that will yield the same result no 

matter who conducts it; free of influence by emotions or personal preferences.

Pallet—a wooden, metal, or plastic framework designed to be picked up by mechanical 

devices such as forklift or pallet trucks for the storage and transport of boxed food 
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commodities inside a warehouse or distribution center. The holding capacity of each 

pallet varies by commodity and by interior building design/space.

Primary Site—the scheduled, preferred site from the State's list of active sites where the 

sample should be collected.

Probability Size Measurements—a measure of size for a unit in a collection from which 

a sample is to be drawn. The probability of selecting a particular unit for the sample is 

proportional to this measure (consequently, it must be known for all units before the 

sample is drawn). 

Processed Commodity—any food product that has undergone physical or chemical 

treatment resulting in a substantial change in the original state of the food. Frozen, 

canned, and dried foods are examples of processed commodities.

Proxy Site—a retail store that may be in close proximity to the Primary or Alternate Site 

and that preferably receives the product directly from the Primary or Alternate Site (in the 

distribution chain). Proxy sites may be used for the collection of PDP commodities that 

have been approved by MPD, usually for products that are not readily available at 

distribution centers and terminal markets.

Quality Assurance (QA)—an integrated system of activities involving planning, quality 

control, quality assessment, reporting, and quality improvement to ensure that a product 

or service meets defined standards of quality with a stated level of confidence. The PDP 

QA programs encompass sampling, laboratory analysis, and data reporting/database 

activities. Quality control (QC) is defined as the activities that are conducted on a 

routine/daily basis to carry out quality assurance (i.e., to reduce error and ensure that 

data are generated and/or processed within known and acceptable limits).

Quarterly Sampling Plan—a document that is transmitted via a memo to Sampling 

Managers that outlines weekly and monthly schedules for the collection of commodities 

and provides a source of information vital to both sample collectors and laboratory 

personnel on upcoming new commodities. Timing of drafts and final Quarterly Sampling 

Plan is as follows:

--45 days prior to beginning of new quarter: MPD draft sent to Sampling 

Managers for their review and comments

--30 days prior to beginning of new quarter: MPD final plan sent to Sampling 

Managers

--15 days prior to beginning of new quarter: each State final sampling schedule

posted to MPD’s Extranet site

Quarterly Sampling Schedules (final)—commodity collection schedules prepared by 

State Sampling Managers and approved by appropriate analyzing laboratory Technical 

Program Managers that list specific sites and dates when PDP commodities will be 
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collected for every month in each quarter. Sampling Managers must post their final 

schedules to MPD’s Extranet site two weeks prior to each new quarter.

 

Random Selection Process/Procedure—statistics of or characterizing a process of 

selection in which each item of a set has an equal probability of being chosen. A system 

for selecting a sample of units from a larger collection [statisticians prefer the word 

"population"] of units in which every member of the collection has a positive probability of 

selection. 

Refrigerated Temperature—a cooled container that can maintain temperatures 

between 33-45oF (1-8oC) for a specified period of time during holding or shipment of 

commodities to their respective laboratory.

Relative or Comparative Volume Information—a method used to calculate and show 

the differences in the volumes of produce that different vendors or collection sites carry

in each participating State [not a technical term per se -- if unit A has volume a and unit 

B volume b, then if A has relative volume a', B has relative volume b' (b/a).] States are 

required to update volume information at least once a year; this information is used by 

USDA-NASS statisticians to make monthly site selections for each State.

Remote Data Entry (RDE)—software system used to enter, review, and submit PDP 

data. The RDE system has two major components, a Windows-based system that 

allows sample collectors to enter and submit an electronic SIF and a Web-based system 

that allows laboratories to enter and submit completed data sets.

Retail Market/Store—a facility in which food is sold directly to the end-user customer.

Sample Information Form (SIF)—a form that contains detailed information on a 

commodity collected for PDP that makes each sample unique. SIFs may be in an 

electronic or paper format and must be emailed or shipped, respectively, for/with each 

set of samples.

 

Semi Annual Program Plan—a statement of work distributed quarterly each year by 

MPD for PDP planning that contains the following information: (1) administrative 

updates; (2) a list of new and revised SOPs; (3) commodity additions, deletions, and 

continuations, including names of laboratories who will be testing the new commodities; 

(4) testing additions, deletions, changes, and continuations; and (5) any other future 

program directions. The program plans often include the Shipping Assignment Charts 

for the upcoming quarter and an updated MPD Contact List.

Shipping Assignment Chart—a quarterly document created by the PDP Sampling 

Manager that contains pertinent collection and shipping information for all the sampling 

States: commodity names and codes that are scheduled for collection, State collection 

numbers, sample amounts/weights, collection changes from the previous quarter, 
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sample start dates, analyzing laboratory names and locations, and special collection 

notes. Current Shipping Assignment Charts are available on MPD’s Extranet site.

Sample—a given number of units, volume, or weight of a specific commodity 

collected at an assigned site on an assigned date. Each commodity sample is 

unique in that its label and associated Sample Information Form (SIF) contain 

information indicating it is different from other samples of the same commodity in at 

least one of the following areas: collection State; collection date; collection site; lot 

number; and origin of grower, packer, or distributor. All units in a fresh sample must 

represent the same lot number, while some processed products can be made up of 

separate lot numbers if approved by MPD. 

Size Measure—comparative volume number to show the size differences in sampling 

sites. (See “Relative or Comparative Volume Information”)

State Sampling Manager—a professional of appropriate education, training, 

experience, or combination thereof, who is responsible for the conduct of a State's 

sampling program and who assures that his/her sample collectors adhere to PDP

Sampling Standard Operating Procedures.

Sterile—free of any living microorganisms, pathogenic or non-pathogenic.

Subjective Selection/Judgment—a selection process that is influenced by emotions or 

personal preferences; not objective. (If something is free of subjective judgment, it is not 

influenced by emotions or personal preference.)

Tamper-Proofing—a method used to prevent accidental or intentional alteration of a 

closed or sealed package.

Terminal Market—an organized market in a city into which large quantities of 

agricultural produce are shipped for distribution and sale, generally to retailers, 

restaurants, and institutions. A collection of vendors/wholesalers doing business in the 

same place.

Vendor—an individual wholesaler (person or agency) who sells food in a terminal 

market. 

Volume Weighting—a way of estimating an aggregate value for a collection of units 

(e.g., a total or a proportion) from a sample that counts each sampled unit differently 

depending on its relevant size ("volume"). Statistics: a coefficient assigned to elements 

of a frequency distribution in order to represent their relative importance. [See “Relative 

or Comparative Volume Information.]
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Voucher—a method of payment for the purchase of fruit and/or vegetables from a food 

vendor. It is a document that acknowledges a liability or provides authorization to pay a 

debt. 

Whirl Pak®—a leak-proof primary sample bag which has twistable tabs near the 

opening that can be manipulated to tie and seal the bag once the bag has been "whirled" 

around on itself several times. There are generic versions of this bag that are 

acceptable for use in PDP sampling.

Wholesale Market—a market in which food is sold to retailers, distributors, or other 

wholesalers who in turn sell to retail or end-use customers. The sale of goods in 

quantity to retailers or jobbers for resale (as opposed to a retail market).