14.1 Introduction
Area sampling frames are a complete set of stratified primary sampling units (PSU)
that are used to select the samples for probability area sample surveys. The PSUs
are composed of mutually exclusive, nonoverlapping land parcels, known as segments. The segments of an area sample survey cover the entire survey area, without
overlap or gap between adjacent segments, and have a known probability of selection which is commonly proportional to their area measurement. Complete coverage
of the survey population combined with a random selection of segments or sampling
units provides the means to obtain unbiased estimates with measurable precision
(Cotter et al. 2010; FAO 1998).
Area sampling frames are used for a variety of surveys ranging from crop acreage
and yield, to soils, livestock, forest and natural resource inventories, and are the
foundation of the agricultural statistics program of the National Agricultural Statistics Service (NASS) and many other statistical survey programs around the world
(Cotter et al. 2010; Ford et al. 1986; Vogel 1995; Nusser and House 2009; Arroway
et al. 2010). Area sampling frames or area frames have been used in NASS since
1954 as a primary tool for conducting surveys to gather diverse agricultural information, notably planted acreage of major crops and economic and chemical use, and
other information.
NASS’s primary area frame-based survey is the June Area Survey (JAS) in which
approximately 11,000 one-square-mile sample segments are visited by survey field
interviewers, known as enumerators, at the beginning of each growing season to
collect crop type and acreage information. Estimates of crop acreage and livestock
inventories are based on these data. The JAS is a component of data collection and
estimation for more than 14 official NASS statistical publications. In recent years,
agricultural surveys have become increasingly relied upon to provide timely, accurate, and useful statistical information for public use. The wide range of crop,
livestock, and economic statistics derived from area sampling frame-based surveys
and published in the NASS official reports helps to reduce the risk of instability for
agricultural operations. For these reasons, the JAS plays a critical role in many of the
NASS programs (USDA NASS 2017c).
The area frames are also used for follow-on surveys such as the Objective Yield
Survey in NASS. Further, every 5 years, additional segments are added to the JAS
for the Agricultural Coverage Evaluation Survey. Data collected from the JAS and
Agricultural Coverage Evaluation Survey segments are used to measure the completeness of the Census of Agriculture mail list. For these applications and more,
area frames are considered “the backbone to the agricultural statistics program of the
National Agricultural Statistics Service” (Cotter et al. 2010).
The accuracy of NASS survey statistics depends on the quality of the NASS area
frames and therefore the techniques used in their construction. The NASS area
frames are based on a stratification of U.S. land cover which classifies land into
different agricultural intensity groups or strata based on percent cultivation in a given
land parcel. The traditional stratification of land cover has been conducted using
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C. G. Boryan and Z. Yang
Area sampling frames are a complete set of stratified primary sampling units (PSU)
that are used to select the samples for probability area sample surveys. The PSUs
are composed of mutually exclusive, nonoverlapping land parcels, known as segments. The segments of an area sample survey cover the entire survey area, without
overlap or gap between adjacent segments, and have a known probability of selection which is commonly proportional to their area measurement. Complete coverage
of the survey population combined with a random selection of segments or sampling
units provides the means to obtain unbiased estimates with measurable precision
(Cotter et al. 2010; FAO 1998).
Area sampling frames are used for a variety of surveys ranging from crop acreage
and yield, to soils, livestock, forest and natural resource inventories, and are the
foundation of the agricultural statistics program of the National Agricultural Statistics Service (NASS) and many other statistical survey programs around the world
(Cotter et al. 2010; Ford et al. 1986; Vogel 1995; Nusser and House 2009; Arroway
et al. 2010). Area sampling frames or area frames have been used in NASS since
1954 as a primary tool for conducting surveys to gather diverse agricultural information, notably planted acreage of major crops and economic and chemical use, and
other information.
NASS’s primary area frame-based survey is the June Area Survey (JAS) in which
approximately 11,000 one-square-mile sample segments are visited by survey field
interviewers, known as enumerators, at the beginning of each growing season to
collect crop type and acreage information. Estimates of crop acreage and livestock
inventories are based on these data. The JAS is a component of data collection and
estimation for more than 14 official NASS statistical publications. In recent years,
agricultural surveys have become increasingly relied upon to provide timely, accurate, and useful statistical information for public use. The wide range of crop,
livestock, and economic statistics derived from area sampling frame-based surveys
and published in the NASS official reports helps to reduce the risk of instability for
agricultural operations. For these reasons, the JAS plays a critical role in many of the
NASS programs (USDA NASS 2017c).
The area frames are also used for follow-on surveys such as the Objective Yield
Survey in NASS. Further, every 5 years, additional segments are added to the JAS
for the Agricultural Coverage Evaluation Survey. Data collected from the JAS and
Agricultural Coverage Evaluation Survey segments are used to measure the completeness of the Census of Agriculture mail list. For these applications and more,
area frames are considered “the backbone to the agricultural statistics program of the
National Agricultural Statistics Service” (Cotter et al. 2010).
The accuracy of NASS survey statistics depends on the quality of the NASS area
frames and therefore the techniques used in their construction. The NASS area
frames are based on a stratification of U.S. land cover which classifies land into
different agricultural intensity groups or strata based on percent cultivation in a given
land parcel. The traditional stratification of land cover has been conducted using
266
C. G. Boryan and Z. Yang