American Community Survey
Cautions, Documentation and Guidelines on Using ACS Data
NOTE: Data are available for some areas, such as Baltimore City with a population of over 600,000, for all three data releases (annual, three-year and five-year). For Kent County, however, with a population of just over 20,000, data are available for three-year and five-year releases only. Data from the different releases should not be mixed, however, so if a comparison of median household income between Baltimore City and Kent County is needed for example, one would have to use the same data set - the three or five-year data for Baltimore City and Kent County to be consistent.
The Census Bureau collects ACS data from a sample of the housing unit addresses in the United States --rather than from the whole population All ACS data are survey estimates. To help you interpret the reliability of the estimate, the Census Bureau publishes a margin of error (MOE) for every ACS estimate.
American Community Survey 1-, 3-, and 5-year estimates are period estimates, which means they represent the characteristics of the population and housing over a specific data collection period. Data are combined to produce 12 months, 36 months or 60 months of data. These are called 1-year, 3-year and 5-year data.
|Distinguishing features of ACS 1-year, 3-year, and 5-year estimates|
|1-year estimates||3-year estimates||5-year estimates|
|12 months of collected data||36 months of collected data||60 months of collected data|
|Data for areas with populations of 65,000+||Data for areas with populations of 20,000+||Data for all areas|
|Smallest sample size||Larger sample size than 1-year||Largest sample size|
|Less reliable than 3-year or 5-year||More reliable than 1-year; less reliable than 5-year||Most reliable|
|Most current data||Less current than 1-year estimates; more current than 5-year||Least current|
|Best used when||Best used when||Best used when|
|Currency is more important than precision Analyzing large populations more current than 5-year estimates||Analyzing smaller populations Examining smaller geographies because 1-year estimates are not available Precision is more important than currency||Analyzing very small populations Examining tracts and other smaller geographies because 1-year estimates are not available|
For more guidelines on understanding and using ACS and sample Power Point presentations: Compass Products and Other Documentation