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ACS 2015 now available

FeaturesGeographiesVariables1 Year3 Year5 YearWhich To Use Order

When to use 1-year, 3-year, or 5-year estimates

Choosing which dataset involves more than simply considering the population size in your area. You must think about the balance between currency and sample size/reliability/precision.

For details, research implications, and examples, see "Understanding and Using ACS Single-Year and Multiyear Estimates," page 9 in General Data Users Handbook [PDF 1.6MB]

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 precise than 1-year, more current than 5-year

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

General Guidance for comparing ACS multiyear estimates
  • If you want to compare estimates for different areas, use the same ACS data file – you should not compare a 1-year estimate for one area to a 3-year estimate for another area.
  • The Census Bureau discourages direct comparisons between estimates for overlapping periods. Instead, compare non-overlapping estimates. Thus you should not compare the 2005-2007 ACS estimates to the 2006-2008 ACS estimates. It is better to compare 2005-2007 ACS to the 2008-2010 ACS estimate.
  • The power of the ACS is in estimating demographic distributions. So users are encouraged to analyze derived measures such as percents, means, medians, and rates rather than estimates of population totals.

For additional guidance in comparing ACS estimates to Census 2000 data the US Census Bureau offers the following tools: for an overview, use the quick guide, to compare by subject browse the subject/topic comparison chart, or use the table comparison tool to search by table number.

For more information you may want to read through the Handbooks that the Census Bureau publishes – they are found on the Census website at:

Series of Handbooks put out by USCB

Handbook for General Data Users


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