Prior to the ACS program, these types of information were collected by the U.S. Census Bureau only every 10 years through the long-form survey of the Census of Population and Housing. Full implementation of the ACS went into effect in 2005, replacing the decennial long-form in future censuses. Unlike decennial censuses that measure a single reference point every 10 years, the ACS is a continuous national survey. The ACS collects data almost daily and summarizes it over 1- and 5-year periods, depending on geographic scale of reporting. Access to more current data has tradeoffs, however, which include smaller samples and subsequently higher levels of variability.
ACS Reporting Requirements
Population size requirements
- 1-year estimates: Only areas with populations over 65,000
- 5-year estimates: Any size area
Estimates by geographic coverage
- U.S., states, metropolitan areas, counties, places: 1- and 5-year estimates (see size requirements above)
- Census tracts: 5-year estimates only
- Block groups: 5-year estimates only
- Zip codes: 5-year estimates only
Guidance for Use of ACS Data
The following guidance for use of ACS data is provided by the U.S. Census Bureau:
Comparing ACS 1-year data with other data
- Generally, you can compare ACS 1-year estimates with Census 2000 and other ACS 1-year data.
- However, since ACS variables change over time, some areas and subjects must be compared with caution, or not compared at all.
Comparing ACS 5-year data with other data
- Generally, you can compare ACS 5-year estimates with Census 2000 data.
- There are differences in question wording, residence rules, reference periods, and the way in which the data are tabulated which can impact comparability.
General Guidance for comparing ACS multiyear estimates
- When comparing estimates for different areas, use the same period length for each estimate. This means you should not compare a 1-year estimate to a 5-year estimate.
- The Census Bureau discourages direct comparisons between estimates for overlapping periods. Instead, compare non-overlapping estimates. This means the Census Bureau discourages comparing, for example, 2006-2010 ACS estimates to 2007-2011 ACS estimates. It is better to compare a 2006-2010 ACS estimate to a 2011-2015 ACS estimate.
- The strength of the ACS is in estimating characteristic distributions. The Census Bureau recommends users compare derived measures such as percents, means, medians, and rates rather than estimates of population totals.
American Community Survey Best Uses
| ACS 1- Year Estimates | ACS 5- Year Estimates |
|---|---|
| Populations of 65,000+ | Populations of any size |
| Smallest sample size (2.1 percent of households) | Largest sample size (approx. 10.6 percent of households) |
| Less reliable than 5-year estimates | Most reliable |
| Most current data | Least current |
| Best used when | Best used when |
| Currency is more important than precision | Precision is more important than currency |
| Analyzing large populations | Analyzing very small populations |
| Examining tracts and other smaller geographies because 1-year estimates are unavailable |
Knoxville Region ACS Data
Geographic coverage
- United States
- Tennessee
- Knoxville-Morristown-Sevierville combined statistical area (2013 boundary)
- Knoxville metropolitan statistical area (2013 boundary)
- Morristown metropolitan statistical area (2013 boundary)
- Counties within the Knoxville-Morristown-Sevierville combined statistical area (2013 boundary)
- Cities within Knox County
- Census tracts within Knox County
- Planning sectors
