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
|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 current data
||Less current than 1-year estimates; more current than 5-year
|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