use microdata areas (PUMAs), which are defined to include about 100,000 people; and

  • limiting the detail that is provided for sensitive variables—for example, assigning a catchall code to income amounts over a certain threshold, such as $100,000 or more, and not identifying the specific amount.

Data Processing—1-Year Period Estimates

The computer programs to generate the ACS 1-year period data products each summer operate on 12 months of data collected in the preceding calendar year. These data include all of the mailed-back, CATI, and CAPI responses that were received in January through December of that year (including additional information obtained by telephone for incompletely filled out mail questionnaires). The major data processing steps are described briefly below.

Coding, Editing, and Imputation

As in the long-form sample, the first data-processing step for the ACS is to assign codes for write-in responses for such items as ancestry, industry, and occupation by using automated and clerical coding procedures. Coding is performed on a monthly basis. Then once a year, the raw data, the codes assigned to write-in items, and various operational data for the responses for the preceding January–December are assembled into an “edit-input file.” Computer programs review the records on this file for each household to determine if the data are sufficiently complete to be accepted for further processing and to determine the best set of records to use in instances when more than one questionnaire was obtained for a household.

Computer programs then edit the data on the accepted, unduplicated records in various ways. Computer programs also supply values for any missing information that remains after editing, using data from neighboring households with similar characteristics in a process called “hot-deck imputation.” The goal of editing and imputation is to make the ACS housing and person records complete for all persons and households

Because of the varying reference periods in the ACS, dollar amounts of income are adjusted for inflation using the national consumer price index for all urban consumers research series (CPI-U-RS) so that every amount reflects the average value of the dollar for the calendar year. For example, a person who reported an income of $20,000 in February 2005 for the period February 2004–January 2005 would have this amount inflated by a figure of 1.031 to give an amount of $20,620. The figure of 1.031 comes from dividing the average annual CPI-U-RS for 2005 (which has the value

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