in addition to residence according to the 2-month rule, in order to make it possible to relate census and ACS results (National Research Council, 2006:Recs. 8-3, 8-4).

We support research with the ACS’s experimental methods panel (see Section 7-C.2) to assess the extent to which respondents give different answers to the decennial census usual residence rule and the ACS 2-month residence rule and the extent to which they follow the specific ACS rules, such as the rule to count boarding school students at home. The inclusion of questions on other residences at which respondents spend time would facilitate the determination of respondents’ usual residence and 2-month residence to use in analyzing the experimental results.7 Such research might in the future lead to improvements in the way in which the 2-month rule is explained to respondents, as well as possibly to a decision to modify the 2-month rule in some respect.

In addition, we support research on the effects of the residence rules, assuming they are applied as intended, on estimates for different geographic areas and population groups. For example, the application of the 2-month residence rule should provide a basis for identifying seasonal fluctuations in population in ways that would not be possible with a usual residence rule. A possibly confounding effect could occur from the 3-month data collection window for each month’s sample that is part of the ACS design. What is the effect, for example, on estimates of occupied versus vacant housing units when a seasonal resident does not respond by mail or CATI and has left the area by the time of the CAPI interview? Questions such as these should be addressed through appropriate research, including experimentation.


Recommendation 4-6: The Census Bureau should conduct experiments to determine the extent to which ACS respondents give different answers to the decennial census usual residence rule and the ACS 2-month residence rule and the extent to which they apply the specific ACS residence rules (for example, reporting commuter workers at the family residence, applying the 2-month rule prospectively). To help clarify residence according to the census and ACS concepts, the experimental questionnaire should ask about other residences at which respondents spend time. The Census Bureau should assess the implications of the experimental results for ACS population estimates for different geographic areas and population groups. Depending on the results, the Census Bureau should consider appropriate changes

7

The ACS questionnaire currently asks three relevant questions (see Table 2-2): whether any household members live at the address year round, number of months members live here, and main reason members stay at the address, but these questions are slated to be eliminated in 2008. Moreover, the questionnaire does not ask for information on other residences.



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