WHAT'S IN A FRAME? 

by Terry Holland 

When I first started working for the Agency and before I had taken a sampling course, I kept 

hearing people talk about "the list frame" and "the area frame." "What are these things called 

frames?" I wondered. I imagined two gilded picture frames hanging on a wall - in one, a great 

list of farmers in tiny print; in the other, a huge detailed map of the United States. How they 

drew samples from these things I had no idea! Obviously I had the concept wrong, so I decided 

to do some digging. I started with Webster's dictionary: 

 frame (n) 1 a: something composed of parts fitting together and united ... 

 2 a: the constructional system that gives shape or strength (as to a building) ... 

 3 c: a structural unit in an automobile chassis supported on the axles and 

 supporting the rest of the chassis and the body ... 

None of the definitions seemed to fit, so I tried another dictionary. The same definitions were 

given: window frames, eyeglass frames, house frames, skeletons, baseball innings, bowling 

frames, film exposures, frame of mind, frame of reference, but no sampling frames! I tried a 

statistical dictionary. No luck! There was no clear definition of a frame. What should I do 

now? 

With more digging, I finally discovered that the concept of the frame is relatively new. First 

stated by Frederick F. Stephan in 1936, the "frame" concept was adopted by the United 

Nations Subcommission on Statistical Sampling in 1948. According to W. Edwards Deming, a 

frame is "a set of physical materials (census statistics, maps, lists, directories, records) that 

enables us to take hold of the universe piece by piece." A universe is simply "all the people or 

firms or material, conditions, concentrations, models, levels, etc., that one wishes to learn 

about ..." 

More simply, a frame is a means by which a universe may be sampled. To select a sample, the 

universe must be divided into parts, called sampling units. The frame is a list or map of all 

sampling units, or a set of rules for identifying sample units. 

When I was in Oregon, I worked on a Filbert Objective Yield Survey. We used a list of all 

filbert orchards in two States, identified by owner, operator, location, size, age, and variety. 

The list was updated every 4 years by a census of bearing and nonbearing orchards. A sample 

of orchards was selected and located. According to specific instructions, enumerators then 

selected three trees in each orchard to be in the sample. In this case, the universe was all 

bearing trees about which we wanted to know how many nuts they would produce. The 

frame was a list of orchards with a set of rules for further identifying trees. 

This example illustrates the requirements of a frame. First, a frame must have enough 

information to define and locate any sampling unit that may be selected. If the sampling unit 

cannot be defined or found, there can be no frame. Even if the owner and operator of each 
orchard changed during the 4 years between updates, the physical location of each orchard 

and tree did not. Second, the frame should cover the entire universe. If the frame covers only 

part of the universe, the results of the survey will apply only to that portion of the universe 

included in the frame. Since it takes 4 years for new filbert trees to come into production and 

the list was updated every 4 years, the frame meets this requirement. If instead the tree 

inventory was taken every 5 years, then every fifth year the results of the survey would 

reflect production from orchards that had been bearing for more than a year, not production 

from all bearing trees. Third, each element of the universe must be included in one and only 

one sampling unit. Obviously, each tree was found in one and only one orchard. 

Over the years, NASS has developed a list frame and an area frame (those things I used to 

wonder about) to support many different survey needs. The list frame is simply a list of farm 

operators and agribusinesses. We maintain names, addresses, telephone numbers, and other 

items that enable us to locate the farm or business, if sampled. We also maintain control data 

that allow us to refine the frame for specific survey designs. Because the person or operation 

reporting may be different from the operator or business sampled, we have developed a set of 

rules to associate reported information uniquely with the name selected. 

The list frame has a major problem - it does not cover the entire U.S. farm population! 

Sources of names for small and specialty farms are difficult to obtain, making construction of 

a complete list of farms nearly impossible. Even if a complete list could be built, it would be 

out-of-date before it could be used. About two-thirds of all U.S. farms are currently available for 

sampling from the list. Fortunately, we can usually compensate for this undercoverage by using 

samples from the area frame to supplement list samples. 

The area frame is simply the entire U.S. land area divided into segments. Unique and 

identifiable boundaries of sampled segments are outlined on maps and photos to enable us to 

locate the segment. We have developed rules that allow us to associate farm operations, grain 

storage facilities, crops, animals, and other agricultural commodities with land inside each 

segment. Every possible item of interest can be uniquely associated with some segment of 

land, so we can say the area frame entirely covers any possible universe. Samples from the 

area frame may not estimate well for rare and specialty commodities, so it is important that 

all operations producing these types of items be maintained on the list. 

You know, if you really think about it, Webster's definitions of frame aren't too far off the 

mark! A sampling frame is composed of parts (sampling units) that fit together and are 

united. In the constructional sense, NASS sampling frames give shape and strength to our 

sample designs. In the automotive sense, the list and area frames support the rest of the 

NASS survey and estimating programs (chassis and body), but without adequate coverage and 

rules of association (axles) the programs are of limited value.