American Community Survey (ACS)

ACS data users often want to compare the current data with data from Census 2000 and previous ACS releases. Some comparisons might be inappropriate due to differences in questions or methods. This page provides guidance on these issues.

For all comparisons users should take a few things into consideration.

1. Geographic boundaries for the area of interest may have changed.
2. Although the ACS produces population, demographic and housing unit estimates, it is the Census Bureau's Population Estimates Program that produces and disseminates the official estimates of the population for the nation, states, counties, cities and towns and estimates of housing units for states and counties. The ACS should be used to examine housing characteristics and demographic, social, and economic characteristics of the population.
3. The weighting for the group quarters (GQ) population is controlled at the state level, but not at the sub-state level. Users may observe greater fluctuations in year-to-year ACS estimates of the GQ population at sub-state levels than at state levels. Substantial changes in the ACS GQ estimates can impact ACS estimates of total population characteristics.
4. There are global differences that exist between the ACS and Census 2000. These include differences in residence rules, universes, and reference periods.

General Guidance

Comparing 2008 ACS 1-Year Data to 2007 ACS 1-Year Data - The Census Bureau supports comparisons made between 2008 ACS 1-year data and 2007 ACS 1-year data. However, data users need to be aware that changes were made to the 2008 ACS questionnaire that impact comparability for some topics. Item by item guidance is provided below for all ACS topics including any new or modified topics in 2008. For another view of all the changes in the 2008 ACS, please visit "New and Notable."

Comparing 2008 ACS 1-Year Data to Census 2000 Data - There are global differences that exist between the ACS and Census 2000. These include differences in residence rules, universes, and reference periods. For example, the ACS uses a "two-month" residence rule - defined as anyone living for more than two months in the sample unit when the unit is interviewed whereas Census 2000 used a "usual residence" rule - defined as the place where a person lives or stays most of the time. The Census Bureau subject matter specialists have reviewed all of these factors and have determined that for most population and housing subjects, comparisons can be made.

Item-Specific Guidance

Specific item-level guidance is provided in the table below. Guidance is given for each item on comparing 2008 ACS 1-year data with Census 2000 data and on comparing 2008 ACS 1-year data with 2007 ACS 1-year data.

The "table crosswalk" identifies the 2008 ACS 1-year detailed tables for a specific item and the corresponding tables in the Census 2000 Summary File 3 (SF 3). In most cases, the 2008 ACS 1-year detailed tables are structured the same as the SF 3 tables. There are some instances in which the ACS tables show more detail or less detail than the SF 3 table.

For a complete list of changes between the 2008 ACS 1-year and the 2007 ACS 1-year detailed tables, please see "list of changes between 2008 and 2007 detailed tables" [Excel 51 KB].

For guidance on comparing 2007 ACS to other data sources, go to Guidance on Comparing 2007 ACS Data to Other Sources.

* Each subject area is listed with its 2-digit code. This code corresponds to the second and third characters of the ACS table number. For example, Table B08303 - Travel Time to Work - has the digits of "08" in the second and third position. This corresponds to the subject Journey to Work; Workers; and Commuting.

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