CENSUS NONSAMPLING ERROR 



The accuracy of the census counts are affected by the 

 joint effects of the sampling errors described in the previ- 

 ous section and nonsampling errors. Extensive efforts 

 were made to compile a complete and accurate mail list for 

 the census, to design an understandable report form and 

 instructions, and to minimize processing errors through the 

 use of quality control, verification, and check measures on 

 specific operations. Nonsampling errors arise from incom- 

 pleteness of the census mail list, duplication in the mail list, 

 incorrect data reporting, errors in editing of reported data, 

 and errors in imputation for missing data. These specific 

 nonsampling errors are further discussed in this section. 

 Evaluation studies will be conducted to measure the extent 

 of certain nonsampling errors such as coverage error, 

 classification error, and item imputation. 



Census Coverage 



The main objective of the census of agriculture is to 

 obtain a complete and accurate enumeration of U.S. farms 

 with accurate data on all aspects of the agricultural oper- 

 ation. However, the cost and availability of resources for 

 this enumeration place restrictions on operationally feasi- 

 ble data collection methodologies. The past five agricul- 

 ture censuses have been conducted by mail enumeration 

 with telephone contact for selected nonrespondents. The 

 completeness of such an enumeration thus depends to a 

 large extent on the coverage of farm operations by the 

 census nail list. 



Historically, the census of agriculture has included 

 approximately 90 percent of the farms in the United States 

 and over 96 percent of the agricultural production. Com- 

 plete enumeration of agricultural operations satisfying the 

 farm definition of $1,000 or more in agricultural sales is 

 complicated by fluctuations in agricultural operations qual- 

 ifying for enumeration, the variety of arrangements under 

 which farms are operated, the multiplicity of names used 

 by an operation, the number of operations in which an 

 operator participates, the accuracy of data reporting, etc. A 

 new mail list is compiled for each census because no 

 current single list of agricultural operations is comprehen- 

 sive. 



An evaluation of census coverage has been conducted 

 for each census of agriculture since 1945. The evaluation 

 provides estimates of the completeness of census farm 

 count and major census data items. In addition, the 

 evaluation helps to identify problems in the census enu- 

 meration and provide information that can form the basis 

 for improvements. The results of the 1987 Coverage 

 Evaluation program will be published in volume 2, part 2. 



The evaluation of coverage conducted in 1987 was 

 designed to measure errors in the census mail list and in 

 farm classification. Mail list error includes a measurement 

 of farms not on the census mail list (undercount), and a 

 measurement of farms enumerated more than once in the 



census (overcount). Classification error includes a mea- 

 surement of farms classified as nonfarms in the census 

 (undercount) and of nonfarms classified as farms in the 

 census (overcount). Classification error arises from report- 

 ing and processing errors. Mail list undercount dominates 

 all coverage errors. Net coverage error is defined as the 

 difference of undercounted and overcounted farms. Mea- 

 surements of these errors, as well as a description of the 

 complete coverage program, will be available in the Cov- 

 erage Evaluation report. 



Mail List Coverage 



A major problem with the use of a mail list for the census 

 of agriculture enumeration is the difficulties that are encoun- 

 tered in compiling a complete list. The percentage of farms 

 on the census mail list varies considerably by State. 

 Several reasons have contributed to farm operators' names 

 not being included on the census mail list — the operation 

 may have been started after the mail list was developed, 

 the operation may be so small as not to appear in 

 agricultural related source lists used in compiling the 

 census list, or the operation may have been falsely clas- 

 sified as a nonfarm prior to mailout. A large proportion of 

 the farms not included on the mail list were small in both 

 acres and sales of agricultural products. 



The 1987 Census of Agriculture Coverage Evaluation 

 used the area segment sample of the 1987 June Enumer- 

 ative Survey (JES) of the National Agricultural Statistical 

 Service (NASS) to estimate farms not on the census mail 

 list. The Census Bureau contracted with the NASS to 

 augment the JES data collection and receive survey data 

 under the confidentiality protection afforded by Title 13, 

 U.S. Code, from all residents of area sample segments 

 with agricultural activity. These survey records were matched 

 to the census mail list. Records that did not match were 

 mailed a census of agriculture report form to estimate mail 

 list coverage. Estimates of farms not on the census mail 

 list used the capture-recapture dual frame estimator that 

 will be described in the Coverage Evaluation report. 



Table G provides coverage evaluation estimates of the 

 number of farms not on the mail list and selected charac- 

 teristics of those farms with their percent relative standard 

 error. The table also provides an estimate of characteris- 

 tics of farms not on the mail list as a percentage of total 

 farms in the State. The estimate of total farms in the State 

 is based on census farm count and the estimated number 

 of farms not on the census mail list. This estimate of total 

 farms in the State was not adjusted for classification and 

 list duplication errors. Estimates of these errors will be 

 made at the regional rather than the State level and will be 

 available in the Coverage Evaluation report. The table 

 provides the standard error (not relative standard error) of 

 this percent estimate. 



Respondent and Enumerator Error 



Incorrect or incomplete responses to the mailed census 

 report form or to the questions posed by a telephone 



1987 CENSUS OF AGRICULTURE 



APPENDIX C C-5 



