In addition to estimates of seasonal population fluctuations, the ACS could be a vehicle for information about multiple residences more generally—for example, people with weekday and weekend homes or students away at college or boarding school. Questions that may be needed to improve reporting of residence using the 2-month rule, such as whether a household member has another residence, could also provide useful information on multiple residences. Such information would be valuable not only for planning and research, but also for designing coverage improvement programs for the decennial census.

The census long-form sample has historically provided the basis for follow-up surveys for specific, relatively small, or “rare,” populations, such as scientists and engineers and low-income minorities. By using the long-form sample to identify a population of interest for follow-up after the census, targeted postcensus surveys could be more cost-effective than nontargeted stand-alone surveys, which require much larger sample sizes to capture enough cases of the rare population of interest.

The ACS can similarly provide the basis for sampling a small targeted population by serving as the initial screener to identify specific households or persons for interview. (ACS data can also be used to identify areas with a higher percentage of the target population for selecting a sample, using more current data than the long-form sample.) The ACS has the advantage that it can be used for this purpose more often than once a decade, although care will need to be taken to minimize respondent burden and provide for informed consent for any follow-on survey.

There is a procedure for identifying and testing new questions to be included in the ACS, which could potentially expand its use as a screener. For example, a question on field of bachelor’s degree is planned for testing in the 2007 Methods Panel. If the question is added to the ACS, it will be used to target a sample of people in science and engineering fields to support the work of the National Science Foundation. Of course, there is a limit on how many questions can be added to the ACS without an adverse effect on response rates and public perception of the survey, unless some questions can be identified for deletion. Moreover, all ACS questions are mandatory, which makes it incumbent on the Census Bureau to consider the response burden of any new questions very carefully.

There is a pressing need for the Census Bureau to conduct research on methods to improve the estimates of population by age, sex, race, and ethnicity that are used as controls for the ACS and serve so many other