Users can ease the transition from using long-form-sample estimates to using ACS estimates for their applications by becoming knowledgeable about general guidelines for effective use of the ACS (3-H.1) and by taking concrete steps in advance to prepare for the time when 1-year, 3-year, and 5-year period estimates will be released each year (3-H.2).

General Guidelines for ACS Use

Abstracting from the specific applications discussed above, this section provides the panel’s basic general guidelines for appropriate use of ACS estimates.

a. Always examine margins of error before drawing conclusions from a set of estimates. Users should follow this practice for the long-form sample, the ACS, and any other survey on which they rely. More specifically:

  • When using ACS data to estimate a number or percentage for a single area or population group, such as a city or county, the ACS period estimate chosen—1 year, 3 years, or 5 years—should satisfy the precision requirements appropriate for the purpose for which it is being used (refer back to Table 2-7a).

  • Five-year period estimates will not be precise for estimates of small population groups (for example, poor school-age children, poor elderly people, minorities, high school dropouts) for areas with fewer than about 50,000 people, which includes most counties, cities, towns, townships, and school districts, as well as every census tract and block group (refer back to Table 2-7a). Consequently, users should work with 5-year period estimates for small areas only with great care.

  • When it is unduly burdensome to examine numerous individual margins of error—as, for example, when working with a large number of 5-year period estimates for multiple geographic areas—users should at least examine some of the individual error margins to check that the estimates are of adequate precision for their purpose.

b. Review the available information about nonsampling errors for estimates of interest and use this information in interpreting findings from the ACS.

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