• Local government users (Section 3-C). Uses of different ACS estimates are discussed separately for big cities (3-C.1) and small, oversampled jurisdictions (3-C.2). Also discussed is the special case of jurisdictions with large seasonal populations (3-C.3).

  • Transportation planners (Section 3-D). Their applications will rely heavily on the ACS 5-year period estimates and also the public use microdata sample (PUMS) files.

  • Academic and other researchers (Section 3-E). Researchers will make heavy use of the PUMS files and of an ACS summary file, similar to Summary File 3 from the 2000 long-form sample that is currently under development.

  • Media outlets and the public (Section 3-F). These groups will likely make the most use of the ACS 1-year period summary estimates provided in profiles, ranking tables, and change tables.

Whatever their category (federal agency, local government, other), users should review other sections in addition to the one addressed to them. Many of the specific applications discussed—each of which illustrates some but not all issues regarding use of ACS data products to replace long-formsample data products—pertain to more than one category of user.

Section 3-G discusses an issue that affects all users—namely, the fact that new population and housing numbers from the decennial census every 10 years will likely interrupt the time series of ACS estimates. The reason is that the ACS estimates for calendar years ending in 0 through 9 each decade will be calibrated at the level of an individual county (or a group of small counties) to annual population estimates updated from the previous census by records of births and deaths and estimates of net migration. A similar calibration will be made to housing unit totals updated from the previous census. When a new census is taken, the census counts will not necessarily coincide with the updated estimates, thereby producing discontinuities in the ACS time series.

The chapter concludes (Section 3-H) by summarizing the panel’s general guidelines for effective use of the ACS and suggesting ways in which users who expect to work extensively with the ACS small-area data can prepare during the ramp-up period from 2006 to 2010, as the first sets of 1-year, 3-year, and 5-year period estimates become available. Many users are rightly concerned, first and foremost, with how well the ACS can serve as a replacement source of useful and usable estimates for planning, research, public education, and a host of other applications that currently rely on the long-form sample. The examples in this chapter serve principally to address this underlying concern about the functionality of ACS data to meet current needs.

The decoupling of long-form-type data from the once-a-decade census,

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