is expressed in terms of the average value of the dollar for the most recent calendar year. For example, for 3-year or 5-year period estimates released in 2010, covering 2007–2009 and 2005–2009, respectively, all income amounts would be adjusted to reflect the average value of the dollar for 2009. Amounts for housing value and costs are also inflated to reflect the average value of the dollar for the most recent calendar year.

While the Census Bureau has not worked out all of the details of the weighting for 3-year and 5-year period data products, the general procedure will be to remove the adjustments to the 1-year period weights for housing unit nonresponse and agreement with housing unit and population controls and to make new adjustments. Unit nonresponse adjustments will be implemented for all occupied housing units for which data were obtained in the relevant 36 months or 60 months. Averages of the independent housing unit and population estimates for 3 years or 5 years, as applicable, will be used to adjust the weights of each housing unit and person for whom data were obtained during the relevant 36 months or 60 months.

The final data-processing steps for the 3-year and 5-year period estimates are to generate the various data products. At this stage, procedures are implemented to protect data confidentiality; also, for the 3-year period estimates, procedures are implemented (as for the 1-year period estimates) to combine categories (or delete entire tables) to meet precision standards. No screening for precision is applied to 5-year period estimates, as they are considered to be the building blocks for user-defined areas, such as groups of census tracts or block groups in a city.


Two paramount benefits that users will gain from the ACS in comparison with the census long-form sample are the more timely issuance of the data and the greater frequency with which the data will be released. Timeliness refers to the speed with which estimates are produced after the data are collected; frequency refers to how often the estimates are produced. A third important benefit will very likely be improved data quality in that the ACS data will likely be more complete and accurate than the long-form-sample data.

Timeliness and Frequency

Instead of producing point-in-time estimates once a decade for governmental and statistical areas, every year the ACS will produce period estimates—5-year period estimates for all areas, including small neighborhoods (census tracts and block groups) and small governmental units; 3-year period estimates for all areas with at least 20,000 people; and 1-year period

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