NONSAMPLING ERRORS 



Mail List Problems 



Each census or survey is subject to error. In addition to 

 sampling variability, errors arise from nonsample sources such 

 as incorrect or incomplete reporting, processing, and the in- 

 ability to obtain a report from each eligible reporting unit. For 

 example, an operator may report the number of hogs and pigs 

 sold but may not report the value of the sale. In other cases, 

 the respondent indicated the presence of an item but not the 

 quantity. The accuracy of a census count is determined by the 

 joint effects of sampling and nonsampling errors. Thus, extensive 

 efforts were made to keep errors introduced during clerical and 

 electronic processing to a minimum level through the use of 

 quality control, verification, and check measures on specific 

 operations. 



CENSUS COVERAGE 



Although a complete and accurate count of farms, land in 

 farms, and farm production is the aim of each nationwide 

 census of agriculture, the complex structure of America's agri- 

 culture makes this difficult to achieve. Among the complexi- 

 ties are the many places to be included, the variety of arrange- 

 ments under which farms are operated, the continuing changes 

 in the relationship of operators to the farm operated, the 

 expiration of leases and the initiation or renewal of leases, the 

 problem of obtaining a complete list of agricultural operations, 

 the difficulty of locating and identifying some types of farms, 

 the operator's absence from the farm during the data collection 

 period, and the operator's opinion that part or all of the opera- 

 tion does not qualify and should not be included in the census. 



An evaluation of coverage has been conducted for each 

 census of agriculture since 1945. Although the primary purpose 

 of these evaluations is to identify problem areas and supply 

 evidence as a basis for improvements, they also provide users of 

 census data with estimates of the completeness of the census 

 counts. The results of the coverage evaluation study were pub- 

 lished for the 1978 census in Volume 5, Special Reports, part 3. 

 An evaluation of coverage was conducted in 1982 to measure 

 the extent of the undercount and overcount of farms in the 

 census. A description of this evaluation will be in a separate 

 Coverage Evaluation report. This report includes estimates of the 

 percentage of all farms, acres, and sales missed in the census. 



Classification Problems 



In 1982, the proportion of farms missed due to misclassifica- 

 tion (about 3 percent) was higher for farms with small values of 

 sales. The rate of misclassification was higher on (1) livestock 

 farms than crop farms, (2) farms with a small number of acres 

 than larger farms, or (3) full-owner farms than tenant or part- 

 owner farms. Full owners were misclassified more often than 

 part owners. Farm operators over 55 years of age were mis- 

 classified more often than younger operators. 



An evaluation study of classification errors was conducted in 

 the 1982 Census of Agriculture and will be reported In Coverage 

 Evaluation. A sample of mail list respondents was selected, and 

 these addresses reenumerated to determine whether they were a 

 farm or nonfarm. Two types of errors were identified; misclassi- 

 fied farms and overcounted farms. Misclassified farms were farm 

 operations included on the mail list but classified in the census 

 as nonfarms. Overcounted operations were nonfarm operations 

 classified in the census as farms. 



A major problem with the use of a mail list is the failure to 

 include all farms on the list. In 1982, approximately 10 percent 

 of all farms were not included on the census mail list. There 

 were several reasons for the farm operator's names not being 

 included on the mail list-the operation may have been started 

 after the mail list source was developed; the operation may not 

 have been included on any source list used to construct the 

 mail list; or the operation may have been removed from the list 

 because of incorrectly identifying duplicates or falsely classi- 

 fying it as a nonfarm prior to mailout. 



A great many of the farms not included on the mail list were 

 small in both acres and sales. The operator in many cases had 

 a full time off-farm job and farmed part time. In 1982, the 

 average size of farms and sales for census published farms and 

 farms not on the mail list is given below. These figures are sub- 

 ject to final review for the Coverage Evaluation report. 



Average size 



Census Farms not on 

 published farms mail list 



Land (acres) ■ 

 Sales (dollars) . 



439 

 $58,816 



58 

 $5,774 



RELIABILITY OF CENSUS ESTIMATES 



The sources of possible sampling and nonsampling errors 

 have been previously discussed. Some sources affected all the 

 data; others affected only certain items or geographic levels. The 

 results of these errors, bias and increased variability, are difficult 

 to measure. 



Census items were classified as either 100-percent or sample 

 items. The 100-percent items were those asked of all farm 

 operators. These included land in farms, harvested cropland, 

 livestock inventory and sales, and crop acreages and quantities 

 (sections 1 to 21 of the census report form). Variability in the 

 100-percent items is due to the variation associated with non- 

 response imputation and response error. Estimation of this 

 variation results in a standard error of an estimate originating 

 in the selection of the sample of small nonrespondents at the 

 State level. Sample items were items asked of approximately 

 1 in 4 farm operators and include value of land and building, 

 value of farm machinery, energy expenses, and selected farm 

 production expenses, such as hired farm labor and interest 

 expense (sections 22 to 28 of the census report form). Varia- 

 bility in estimates of sample items is the effect of the sample 

 selection and estimation procedure and all the factors affecting 

 the variability of lOOpercent items. 



In the 1982 Census of Agriculture, the sample used is one of 

 a large number of all possible samples of the same size that 

 could have been selected using the same sample design. Esti- 

 mates derived from the different samples would differ from 

 each other. The difference between a sample estimate and the 

 average of all possible samples is called the sampling deviation. 

 The standard or sampling error of a survey estimate is a measure 

 of the variation among the estimates from all possible samples, 

 and thus is a measure of the precision with which an estimate 

 from a particular sample approximates the average result of 

 all possible samples. The relative standard error of estimate 

 (percent) is defined as the standard error of the estimate divided 

 by the value being estimated. 



A-12 APPENDIX A 



1982 CENSUS OF AGRICULTURE 



