flexibility to researchers. For example, in analyzing economic change, they can plan to use two (or more) PUMS files that coincide with different stages of a recession and subsequent recovery. Such an analysis was not possible with the once-every-10-years long-form-sample PUMS. The identification of PUMAs of about 100,000 population on each year’s ACS PUMS file also affords flexibility for analysis.
A drawback of the ACS 1-year PUMS files, as noted above for transportation, is the larger margins of errors compared with the 2000 long-form-sample 5 percent PUMS file. Many research uses of the PUMS data can benefit from combining two or more ACS PUMS files to increase the sample size for the analysis and thereby increase the precision of estimates. Researchers may be able to develop custom PUMS files for particular applications—such as a merged file of two or more 1-year PUMS for analyzing economic returns to education—that can be shared with other researchers.
Researchers will also need to grapple with the different reference periods for different respondents in the ACS PUMS files and develop appropriate analytical strategies. For income amounts for the previous 12 months, the Census Bureau will provide the reported amount, not adjusted for inflation. It will also provide a single inflation factor, which will adjust the values, on average, to July dollars for the latest year covered in a PUMS file (for example, 2005 for the 2005 PUMS file, which contains income reference periods that span January–December 2004 through December 2004–November 2005). A single inflation factor is used because the ACS PUMS files do not indicate the month of interview in order to protect confidentiality. Reconsideration of this decision and inclusion of the month (or season) of interview in the PUMS records and in selected summary tables would greatly increase the analytical value of the files (see Section 4-D.1).
This section discusses using ACS profiles and rankings, which will be appealing products for occasional users and the media (refer back to Box 2-2). It also discusses comparisons of ACS estimates with other data sources, which can confuse users when differences between the ACS and the other data sources are not understood.
Journalists who frequently use statistical information to track local, regional, and national trends will use not only the ACS profiles and rankings, but also more detailed tables. They, like other involved federal, state, and local data users, will need support from the Census Bureau to understand how to properly apply the data (see Section 7-A).