General Questions
How Was the Census Conducted?
Census Data Compared to Other Data
Questions Addressing Specific Data Tables
How was the Census Conducted
Why are there two columns of 1997 numbers in the 2002 publication?
What statistical methodology is used to complete the Census? What is "Coverage Adjustment"?
How do these adjustments affect data at the County Level?
What is the accuracy of the results?
How do we account for farms that do not respond to the Census?
Why did the U.S. number of farms with 2,000 acres or more decrease in 1997 after adjusting for undercoverage?
Are the unadjusted numbers available like they were in the past?
Does NASS change its "Official Estimate" based on the Census results? Does NASS adjust the Census counts to match their official estimates?
Why weren't Alaska and Hawaii adjusted for coverage like all other states?
I've been tracking Census data for years. How can I interpret the coverage adjusted numbers?
We've used Agriculture and Economic Census data together to profile America. Has anything changed for the Economic Censuses and how do they differ?
My local government uses your Census data to make decisions in my local jurisdiction. How do changes to the way you conduct the Census affect me?
Where do you place crop acres, livestock and other data when a farm operates in more than one county? In addition, for Contractee Operations, are the data in the county of the contractor of contractee?
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WHY ARE THERE TWO COLUMNS OF 1997 NUMBERS IN
THE 2002 PUBLICATION?
Past censuses showed coverage
measures only for a limited set of data items and these were not in the
main tables. In order to provide the most complete picture of agriculture,
all data in the 2002 Census of Agriculture reflect coverage adjusted
totals. In order to have a bridge for historical comparisons, the 1997
numbers have also been adjusted and shown in these tables.
WHAT STATISTICAL METHODOLOGY IS USED TO COMPLETE
THE CENSUS? WHAT IS COVERAGE ADJUSTMENT?
NASS collects
census data from a list of all known potential agriculture operators. This
list was assembled from previous census records, State and Federal
agencies, trade associations and similar organizations that could be
identified as associated with agriculture. However, the list is never
complete. Producers go in and out of business every day and many small
operations are simply never identified. In order to measure the
incompleteness of the Census Mail List, i.e., determine how many producers
are not on the list, NASS conducts an Area Frame Survey each year. This
survey is based on sample tracts of land randomly selected throughout the
conterminous U.S. Every agricultural operator discovered within the
selected tracts is interviewed and all land in each tract is accounted
for. This process ensures that every agricultural operation in the U.S. is
eligible for selection. The results of this survey are then compared with
the Census Mail List to determine the level of completeness of the list
and characteristics of operations and operators that were missed. Census
data can then be weighted based on the characteristics of operations who
did not appear on the Census Mail List. All data included in census totals
are reported by census respondents. Some records have a weight greater
than 1 to account for similar operations missing from the list.
Classification and measurement errors were handled through the use of
commodity targets in the coverage adjustment process. Attempts were made
in the analysis and processing of data to identify and make corrections
for duplication and misclassification. Operation weights by type and size
were adjusted by the level of commodity incompleteness known from reliable
sources. This could result in slight adjustments of numbers either up or
down.
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HOW DO THESE ADJUSTMENTS AFFECT DATA AT THE COUNTY
LEVEL?
The coverage adjustments are generated and
therefore most accurate at the state level. The state level data
adjustments for undercoverage are then allocated among census records
having reported data with appropriate characteristics in the
counties.
WHAT IS THE
ACCURACY OF THE RESULTS?
The data to be released in
2002 census publications are the result of a consistent statistical
process designed to provide the truest picture of US agriculture. As such,
those data present a more complete and representative picture of the
agriculture and farming operations in each State and county than has been
possible in past census publications. The more rare the commodity or
characteristic included in the summary tables, the more chance there will
be for anomalies resulting from higher weights on some records.
Adjustments for undercoverage account for approximately 2.4 percent of
land in farms and 2.9 percent of product market value.
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HOW DO WE ACCOUNT FOR FARMS THAT DO NOT RESPOND TO THE
CENSUS?
NASS maintains a list of agricultural
producers which is used to generate the Census Mail List. Everyone on this
list was mailed a 2002 Census of Agriculture report form. Although
multiple attempts were made to obtain a response from each operator, some
producers did not return their form. Accounting for farms that did not
file a return is done through a nonresponse adjustment. A weight is
applied to the good responses from similar operations to compensate for
this nonresponse. The data in the 2002 Census of Agriculture are reported
data adjusted for nonresponse. This adjustment has also been made
throughout the history of the census.
The response rate has steadily increased over the course of the past
several censuses. The overall response rate for the 2002 Census of
Agriculture was 88 percent.
WHY DID THE U.S. NUMBER OF FARMS WITH 2,000 ACRES OR MORE
DECREASE IN 1997 AFTER ADJUSTING FOR
UNDERCOVERAGE?
This is an unusual result of the
change in methodology. Nonresponse weighting in 1997 produced one set of
weights for census records which were rounded to integers. In 2002, the
1997 data were summarized using the new methodology to be able to compare
data with 2002 census data. The new weights rounded differently and
resulted in a slightly smaller total (-0.25%) for farms with 2,000 or more
acres.
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ARE THE UNADJUSTED NUMBERS AVAILABLE LIKE THEY WERE IN
THE PAST?
Data adjusted only for nonresponse for
2002 are not readily available and NASS does not plan to publish them.
Census totals based solely on list records are subject to variation in
list coverage between censuses and therefore may not be truly comparable.
In other words, even though the same census process was used to count
known operations in 1997 and 2002, the number of known operations included
on the census list was different in 1997 than in 2002. Better indications
of overall changes are reflected in the comparable complete data totals
for 1997 and 2002. The "old" way loses comparability due to changes in
list coverage. We would recommend against using these numbers. If data
users have a specific request for unadjusted numbers this request should
be submitted via normal data lab procedures. Each request will be reviewed
and must be approved by the Associate
Administrator.
DOES NASS
CHANGE ITS "OFFICIAL ESTIMATES" BASED ON THE CENSUS RESULTS? DOES NASS
ADJUST THE CENSUS COUNTS TO MATCH THEIR OFFICIAL
ESTIMATES?
NASS continues to review census results to
evaluate and revise official estimates. Revisions to major estimates are
published in a series of historical bulletins. During 2004, twenty one
historical bulletins will be published. Similarly, NASS has also always
looked to other sources of reliable data (both internal and external) as a
check during data analysis and processing of the census. This includes a
review of NASS official estimates and estimates from other sources. For
example, livestock slaughter provides an indication of earlier livestock
inventory. . Census data, survey data, market data, and administrative
data all serve to benchmark the best numbers for agriculture.
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WHY WEREN'T ALASKA AND HAWAII ADJUSTED FOR COVERAGE
LIKE ALL OTHER STATES?
No data from area frame
samples were available in these States so there was no statistical basis
to make a coverage adjustment.
I'VE BEEN TRACKING CENSUS DATA FOR YEARS. HOW CAN I
INTERPRET THE COVERAGE ADJUSTED NUMBERS?
The 1997
census provides a bridge between the list only census approach (prior
method not adjusted for coverage) and total census results (new method
adjusted for coverage). Number of farms changed the most because of small
farms missing from the list. Relatively small changes to land, production,
and economic data resulted from coverage adjustments. Changes are
reflected from 1997 to 2002 on a coverage adjusted basis. (See Appendix C
for relative change resulting from nonresponse and coverage
adjustments.)
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WE'VE USED AGRICULTURE AND ECONOMIC CENSUS DATA
TOGETHER TO PROFILE AMERICA. HAS ANYTHING CHANGED FOR THE ECONOMIC
CENSUSES AND HOW DO THEY DIFFER?
The availability of
more complete lists of businesses for other economic censuses gives those
sectors an advantage over agriculture. The new 1997 and 2002 Census of
Agriculture totals are now more comparable with other businesses when
evaluating characteristics in different economic
sectors.
MY LOCAL
GOVERNMENT USES YOUR CENSUS DATA TO MAKE DECISIONS IN MY LOCAL
JURISDICTION. HOW DO CHANGES TO THE WAY YOU CONDUCT THE CENSUS AFFECT
ME?
Census results (as well as all NASS statistics)
are publicly available to everyone. NASS considers ways in which data may
be used when deciding what statistics to publish and how to generate them.
In the past, coverage adjusted numbers were not available for all items.
The new census numbers may not be directly comparable to data that users
may have relied on in the past, but the new 2002 census provides the best
data for decision makers. Impact resulting from the change to more
complete representation for agriculture may be evaluated using the 1997
bridge year.
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WHERE DO YOU PLACE CROP ACRES, LIVESTOCK AND OTHER
DATA WHEN A FARM OPERATES IN MORE THAN ONE COUNTY? IN ADDITION, FOR
CONTRACTEE OPERATIONS, ARE THE DATA IN THE COUNTY OF THE CONTRACTOR OR
CONTRACTEE?
The county in which the largest value of
agricultural products were raised or produced is the principal county in
which the reported farm or ranch data will be published.. . Generally,
when more than one county or State is reported, all data are allocated to
the principal county. However, reports received with land in more than one
county or State were split into two or more separate reports if the data
published collectively are extreme principal county or state level data.
For contractee operations, all data are published in the county which the
commodity was produced.
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