complete information. Moreover, there was no telephone follow-up to fill in missing items on mailed-back questionnaires. Consequently, missing data rates were very high for many long-form questionnaire items in 2000—considerably higher than in the ACS to date (see Section 2-B.2 below).

Data Products

The ACS will produce data products that resemble those from the 2000 long-form sample. The products will be available primarily through the American FactFinder on the Census Bureau’s web site: (see Box 2-2). Because of the continuous design of the ACS, its data products will differ in two important respects from the long-form-sample products. First, the ACS data will be available every year instead of once a decade. As was just done for the ACS 2005 data, each year’s data products will be released in waves from August through November.2 Second, the ACS data that are released each year will not pertain to a point in time, like the long-form-sample data for Census Day; instead, they will be cumulated over a 12-, 36-, or 60-month period for governmental and statistical units depending on population size in order to provide sufficiently precise estimates for publication (see Table 2-5).

ACS products will include tables and profiles of characteristics for governmental and statistical areas; see Box 2-2. The confidentiality of these products will be protected by various means. One method is to combine detailed categories into broader categories when the individual categories contain too few sample cases. Another method is termed “data swapping,” in which computer programs may swap the data for an entire household that is at risk of being identified (for example, the only minority household in a block group) with the data for another similar household in a different area. Only a small percentage of records, which are never identified, are swapped. In addition to the various procedures that are implemented to protect confidentiality for the 1-year, 3-year, and 5-year period estimates, the Census Bureau will combine individual categories and even delete entire tabulations from 1-year and 3-year period products when the sampling errors are very large (see Chapter 4 for details).

ACS products will also include public use microdata samples (PUMS). PUMS files comprise samples of individual records, suitably processed to protect confidentiality by such means as:

  • deleting names and addresses from the records;

  • limiting geographic identification to large areas known as public


See for the release schedule for data products from the 2005 ACS.

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