Basic kinds of information that users need to understand in order to make the transition from the long-form sample to the ACS, including the implications of differences for data quality and utility, include:

  • Differences between the long-form-sample and ACS questionnaires: the format of the questionnaires, the application of residence concepts, the reference periods for questions, and the wording of questions.

  • Differences between the long-form-sample and ACS data collection processes: an understanding of how the ACS data are collected, using different modes, from a series of monthly samples supporting annually updated 1-year, 3-year, and 5-year period estimates for different levels of geography.

  • Differences between the long-form sample and the ACS in the accuracy and geographic specificity of population and housing unit controls that are applied to the estimates.

  • How to compare ACS estimates to the 2000 census long-form sample (and other surveys) in light of differences between them—in particular, how to make comparisons for the 2005 ACS estimates, which pertain to households only and do not include group quarters.

Information relevant to methods and practices for using the ACS that users need to understand include:

  • The provision of data from the ACS, including: the various formats for obtaining data, the geographic levels of data availability, and the trade-offs between different data products. Data access needs to be emphasized, via the American FactFinder web portal, data on CDs and DVDs, and data available from the Census Bureau’s FTP sites.

  • The sampling error of estimates for 12-month, 36-month, and 60-month intervals and how to interpret variability.

  • How to interpret multiyear period estimates.

  • How to gauge change over time using multiyear estimates and how to conduct comparisons across areas.

  • Special issues for small-area data, focusing on strategies to increase precision at a small-area level, such as combining information across time and geography.



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