• ACS 3-year and 5-year period estimates do not refer to a particular year, such as the end year or the middle year. They are period estimates—averages of characteristics over a 36-month or 60-month period—and should be labeled as such. Otherwise, readers may draw an incorrect inference—for example, assuming that a 5-year period estimate of 15 percent poverty is the rate for the end year, when the end-year rate could be considerably higher or lower.

  • ACS 1-year period estimates are also an average over 12 months (except for the special estimates released in June 2006 for January–August 2005 and September–December 2005 for areas affected by Hurricanes Katrina and Rita).

i. Use ACS 3- and 5-year period estimates for income, housing value, and housing costs with care. To compensate for the differing time periods for which dollar amounts are collected, those amounts are adjusted to a common calendar year by the change in the national CPI. This inflation adjustment expresses all of the reported dollar amounts in a comparable manner with regard to purchasing power as of the most recent calendar year in the period. However, the resulting estimates should not be interpreted as current-year estimates.

j. Use care in comparing ACS estimates with estimates from other data sources, including the 2000 long-form sample and other surveys, and be cognizant of the differences that could affect the comparisons. Such differences may include population coverage, sample size and design, reference periods, residence rules, and interview modes.

Suggestions for Users During the Ramp-up Period

In the next few years, users who plan to make extensive use of the ACS will have an opportunity to prepare for the full range of 1-year, 3-year, and 5-year data products that will be available beginning in 2010. It is important for users—including federal, state, and local agencies, and private organizations—not to stint attention or resources in order to make the most of this opportunity, so that they are well prepared to work with the full richness of the ACS data by 2010.

We outline below some of the steps that the technical staff of an agency can take to ensure that their agency is well prepared to work with the ACS data (see also the recommendations in ORC Macro, 2002:Ch. 10).

a. Steps to prepare agency management:

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