or a total of 3 million annual households.3 Over a decade, the ACS will survey approximately 30 million addresses; for comparison, 17 million housing units were surveyed by the long form at one time in the decennial census.
A key function of the ACS is to produce estimates for various levels of geography (from small areas to the total nation) and other population groupings. The ACS provides estimates annually for areas (and population groups) of 65,000 or more people; these estimates are scheduled to be made available in the summer or early fall for the previous year’s sample.4 To attain similar reliability to that provided for some of the small groups in the 2000 decennial census, the ACS estimates for the smallest areas or population groups must be based on data aggregated over 5 years.
The problem of the reliability of data for the smallest areas (such as counties) presents an equivalent statistical problem to the problem of the reliability of estimates for small (rare) subpopulations (small domain estimates), such as scientists and engineers, in terms of sample size considerations. Both small-area and small-domain estimates are subject to insufficient sample sizes to produce sufficient reliability. The National Science Foundation (NSF) faces a reliability problem in using the ACS as the NSCG sample frame not because it wishes to produce small-area estimates, but because it needs the ACS sample size for rare populations.
A recent National Research Council (2007) report, Using the American Community Survey: Benefits and Challenges, points out that there are some important differences between the ACS and the decennial long-form census. One, such difference is that ACS data products are 1-year, 3-year, and 5-year period estimates that average 12, 36, and 60 months of data, respectively. In contrast, the 2000 long-form sample of more than 16 million responding households obtained data for one fixed time—Census Day, April 1. In comparison with the long-form sample, the report suggests that the ACS has three major benefits:
Timeliness: ACS data products are released 8-10 months, instead of 2 years, after data collection.
Frequency: ACS data products are updated every year instead of every 10 years, which will make it possible in many areas to track trends in population characteristics that are important for understanding the science and engineering (S&E) workforce.
Quality: Higher quality of the data in terms of completeness of response to the survey items. The higher response rates for the