Table 13.--Distribution of workers who did farm wagework only and workers who did both farm and nonfarm wagework, by selected characteristics, 1969 wagework only Workers who did both farm and : Farm and nonfarm : : Nonfarm APPENDIX A SOURCE AND RELIABILITY OF THE ESTIMATES Source of data. --The estimates in this report are based on data obtained in December 1969 through supplementary questions in the Current Population Survey of the Bureau of the Census. The sample is spread over 449 areas comprising 863 counties and independent cities, with coverage in each of the 50 States and the District of Columbia. Approximately 50,000 occupied households are designated for interview each month. Of this number, 2,250 occupied units, on the average, are visited but interviews are not obtained because the occupants are not found at home after repeated calls or are unavailable for some other reason. In addition to the 50,000 there are also about 8,500 sample units in an average month which are visited but are found to be vacant or otherwise not to be interviewed. The estimates in this report concern persons 14 years of age or older who did farm wagework in 1969. This data was compiled from supplementary questions to the Current Population Survey asked only if a person 14 years of age or older had performed farmwork for wages or salary during 1969. These questions concerned number of days of farm wagework, farm wages, migratory status, nonfarm wagework and nonfarm wages, chief activity in 1969, residence, and other matters. Not included in this report are hired farmworkers who died, who entered the Armed Forces, or who were removed from the civilian noninstitutional population for other reasons prior to the survey. Also not included are foreign nationals who did farm wagework in this country and returned to their homes before the survey. The number of foreign nationals admitted declined sharply after the termination of Public Law 78 in December 1964, and in 1969 totaled only 15,830. 1/ The total number of persons excluded from this report probably does not exceed 400,000. The estimating procedure used in this survey involved the inflation of the weighted sample results to give independent estimates of the civilian noninstitutional population of the United States by age, color and sex. These independent estimates were based on statistics from the 1960 Census of Population; statistics of births, deaths, immigration and emigration; and statistics on the strength of the Armed Forces. Reliability of the estimates.--Since the estimates are based on a sample, they may differ somewhat from figures obtained if a complete census had been taken using the same schedules, instructions, and enumerators. As in any survey work, the results are subject to errors of response and reporting as well as being subject to sampling variability. The standard error is primarily a measure of sampling variability, that is, of the variations that occur by chance because a sample rather than the whole of the population is surveyed. As calculated for this report, the 1/ Farm Labor Developments, Manpower Administration, Dept. of Labor. standard error also partially measures the effect of response and enumeration errors but does not measure any systematic biases in the data. The chances are about 68 out of 100 that an estimate from the sample would differ from a complete census figure by less than the standard error. The chances are about 95 out of 100 that the difference would be less than twice the standard error. The figures presented in tables 14-18 are approximations to the standard errors of various estimates shown in this report. In order to derive standard errors that would be applicable to a wide variety of items and could be prepared at a moderate cost, a number of approximations were required. As a result, the tables of standard errors provide an indication of the order of magnitude of the standard errors rather than the precise standard error for any specific item. Table 14.--Standard errors for estimated numbers of persons who did farm Estimated percentages and estimated averages are computed by using sample data for both numerator and denominator. The reliability of these estimates depends both upon the size of the estimate and the size of the totals upon which the estimates are based. Estimated percentages are relatively more reliable than the corresponding estimates of the numerators of the percentages, particularly if the percentages are 50 percent or more. Table 15 contains the standard errors of estimated percentages. Averages are subject to large sampling variability since the sample estimate of an average is affected by extreme estimates. If sensitive indicators are needed, other types of statistics, such as medians, should be considered. Tables 16, 17, and 18 contain the standard errors of estimated averages. Table 15.--Standard errors of percentages of persons who did farm wagework Table 16.--Standard errors of average number of days of farm wagework Note: Table 16 pertains to averages computed from distributions allowed to vary over the entire range of days worked. Standard errors for truncated distributions (e.g., workers with less than 25 days of farm wagework) are somewhat smaller. Table 17.--Standard errors of average annual earnings from farm wagework Table 18.--Standard errors of average daily earnings from farm wagework |