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The American Community Survey (ACS) is an ongoing survey from the U.S. Census Bureau that provides vital social, economic, housing, and demographic data. Unlike the decennial census, which is a point-in-time count every ten years, the ACS provides "period estimates" representing data collected over a specific window of time. The Census Bureau offers two different ACS period estimates, 1-year and 5-year, to accommodate the need for both data timeliness as well as for data availability for small geographic areas.
The 1-year estimates provide the most current ACS data available, summarizing survey responses collected over a single calendar year. Because these estimates rely on a smaller sample size, they are published only for geographic areas with populations of 65,000 or more. This includes all states, as well as many large counties and cities. A primary advantage of the 1-Year ACS is timeliness, making the data useful for analyzing recent trends and short-term changes in the characteristics of larger populations.
The ACS 5-year estimates combine data collected over 60 months to produce detailed statistics for all geographic areas, including small towns, census tracts, and block groups. By pooling five years of data, the sample size is increased significantly, supporting the production of estimates at smaller geographies as well as for more detailed cross-tabulations. These estimates are best used when geographic granularity and precision are more important than timeliness.
One of the most frequent uses of American Community Survey (ACS) data is to make comparisons between estimates - across different geographic areas, different time periods, or different population subgroups.
Comparing American Community Survey (ACS) estimates involves more than determining which statistic is higher or lower. Users should also conduct statistical testing to make sure differences are statistically significant and are unlikely to have occurred by chance. This testing takes into account the margin of error (MOE) associated with survey estimates, which are based on responses from a sample of the full population.
The Census Bureau provides a tool to help data users conduct statistical tests.
Census Bureau's Excel-based Statistical Testing Tool
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