Comparisons of the C2SS and the 2000 long-form-sample estimates for individual items cannot establish which is closer to a measure of truth—additional research would be required to examine this issue, using such techniques as matches with consistently defined administrative records and reinterviews of households. Yet such comparisons can identify the extent to which items are broadly consistent between the two surveys, thereby giving users confidence in the ACS as a replacement for the long-form sample. Complete consistency should not be expected even with the same questions because of differences in reference periods and residence rules, question formatting, editing, interview mode, and other survey procedures, yet the finding of major differences would be cause for disquiet and suggest further needed research.
The comparisons of the C2SS and the 2000 long-form sample for household residents found that most items were broadly consistent between the two sources at the national level. Individual comparisons performed for 18 of the 36 counties in the ACS test sites also found a high degree of consistency for most items. (It was not possible to perform comparisons for group quarters residents because they were not included in the C2SS.) “Driving to work alone” was an instance of a category in which national estimates were similar between the C2SS and the long-form sample, but estimates differed substantially for some of the counties that were examined individually. For this category, the C2SS estimates were appreciably higher in three counties and appreciably lower in three counties than the corresponding long-form-sample estimates (U.S. Census Bureau, 2004b:23).
National-level differences between the two surveys that were statistically and substantively significant occurred for race, ancestry, vacancy status, tenure (owner/renter), number of rooms in the housing unit, disability status for people ages 5–64, employment status, and median income. Users should always exercise care when comparing estimates from any of the ACS data sets (2005, 2001–2004 test surveys, C2SS) with the 2000 long-form sample because of differences in the ACS and long-form-sample design and operations. They should be particularly careful when making comparisons for the items discussed below.
Race and Ethnicity The C2SS estimated a higher percentage of “white alone” and a lower percentage of “some other race alone” compared with the 2000 long-form sample (77.5 versus 75.3 percent for “white alone” and 3.9 versus 5.5 percent for “some other race alone”). These results appear due in part to differences in wording and format of the race and ethnicity questions, which the Census Bureau is investigating (U.S. Census Bureau, 2004a:32). Another contributing factor is that census enumerators, who