sample size is only about three-fourths that of the long-form sample and that the ACS then uses subsampling for the CAPI interviews. For planning purposes, the Census Bureau estimated that the sampling errors (known as the standard errors) of the ACS 5-year period estimates would be about 20 percent greater than the errors of the long-form-sample estimates, but recent work (Starsinic, 2005) suggests that the ACS sampling errors will exceed the long-form-sample errors by about 50 percent.
The ACS design, like the long-form-sample design, oversamples very small governmental jurisdictions (refer back to Table 2-3a). This oversampling reduces the sampling errors of estimates for those units, but it increases the errors for larger areas that are undersampled, as well as somewhat increasing the errors for larger units that include some oversampled and some undersampled areas relative to a design with the same sampling rate for all areas.
The subsampling used for CAPI interviews in the ACS increases sampling error for two reasons: first, the subsampling reduces the final sample
Brief Descriptions of Statistical Terms Used in This Report
Consider the example of MEDIUM CITY, 5-Year Period ACS Estimate (see Tables 2-7a, 2-7b, and 2-7c). Assume that MEDIUM CITY has a population of 100,000 with an estimated 20,000 school-age children, of whom 3,000 (15 percent) are estimated to be poor. For a 15.0 percent poverty rate for school-age children with a 1.28 percentage point standard error: