ACS: Multiyear Estimates Choosing between 1-year and 3-year

Users of data for the Nation, States, Congressional Districts, counties, metropolitan areas and other geographical areas with populations of 65,000 or more now have two sets of estimates available: ACS 1-year estimates and ACS 3-year estimates. There are several factors that data users should consider when choosing between these estimates.

The ACS 3-year estimates are based on a larger sample and are therefore more reliable but they use data for earlier time periods and are therefore less current. The ACS 3-year estimates include about three times as many sample interviews as the ACS 1-year estimates but a third of those interviews are three years old and a third are two years old. When deciding between ACS 1-year and 3-year estimates users must balance the need for precision against how rapidly the estimate is changing over the 3-year period.

The ACS 3-year estimates are typically preferable for estimates based on small populations. An estimate of a characteristic can have an acceptably small standard error when it applies to the full population of a published geography. However, the estimate of that characteristic may have an unacceptably large standard error when it applies to a subset of the population of the same geography. This is because the size of the population determines how large the sample is for the estimate. An example of such a situation could be the percentage of families with a female householder, no husband present, and with related children under 5 whose income in the past 12 months is below the poverty level.

Use ACS 1-Year Estimates:

For geographies with a population of 65,000 or more when currency is more important than the precision of the estimates (and one is not analyzing a small population).

Use ACS 3-Year Estimates:

For geographies with a population from 20,000 to 64,999 because 1-year estimates are not available for these areas.
For geographies with a population of 65,000 or more when analyzing data for small populations or when the precision of the estimates is more important than the currency of the data.

For more information on multiyear estimates and choosing between the 1-year and 3-year estimates see the following document:
Statistical Issues of Interpretation of the American Community Survey's One-, Three-, and Five-Year Period Estimates [678K]

Using Multiyear Estimates

What is an ACS multiyear estimate?

What types of geographic areas are published for the 1-year and 3-year ACS?

Four things you should know about how ACS multiyear estimates are produced

American Community Survey (ACS)

Using Multiyear Estimates: Choosing Between ACS 1-year and 3-year Estimates