The American Community Survey is the ambitious new national survey from the U.S. Census Bureau that is replacing the long form portion of the decennial census for the new millenium. While some
version of this survey has been in the field since 1999, it was not fully implemented in terms of coverage until 2006. In 2005 it was expanded to cover all counties in the country and the 1-in-40 households sampling rate was first applied. However, persons living in group quarters (such as nursing homes, dormitories and prisons) were not added to the survey until 2006. (The original plan was to begin GQ coverage in 2005 but last-minute budget reductions delayed it for a year.)
The full implementation of the (household) sampling strategy for ACS entails having the survey mailed to about 250,000 households nationwide every month of every year and was begun in January 2005. In January 2006 sampling of group
quarters was added to complete the sample as planned (albeit several years later than originally planned.) In any given year about 2.5% (1 in 40) of U.S. households will receive the survey.
Over any 5-year period about 1 in 8 households should receive the survey (as compared to about 1 in 6 that received the census long form in the 2000 census). Unfortunately, receiving the survey is not the same as responding to it, since the Bureau has adopted a strategy of sampling for non-response. This has resulted in something closer to 1 in 11 households actually participating in the survey over any 5-year period.
Data Release Plan Based on Population Size of Geographic Area
Data based on the ACS surveys for any calendar year will be published in the late summer of the following year for geographic areas with a minimum of 65,000 population. For smaller areas the Bureau will only publish data based on surveys for multiple consecutive years as follows:
In addition to the population threshold rules that are used to limit the publication of data for geographic areas the Bureau also applies their "data release rules" for each
table for each geographic area (that passes the total population threshold filter). Basically they analyze the cells of a table and assign a
measure of the statistical reliability of each cell based on the margin of error. We have indicated our dismay at the algorithm elsewhere (see "Thing 6" in
our Ten_Things to Know... page). The link there to the document that describes
the algorithm is broken, but we found it (or at least something quite similar) at http://www.census.gov/acs/www/Downloads/survey_methodology/acs_design_methodology_ch13.pdf .
The following excerpt from the 8-page document outlines the method. Be sure to note the final sentence. :
Data Release Rules
Even with the population size thresholds described earlier, in certain geographic areas some very
detailed tables might include estimates with unacceptable reliability. Data release rules, based on
the statistical reliability of the survey estimates, were first applied in the 2005 ACS. These release
rules apply only to the 1- and 3-year data products.
The main data release rule for the ACS tables works as follows. Every detailed table consists of a
series of estimates. Each estimate is subject to sampling variability that can be summarized by its
standard error. If more than half of the estimates in the table are not statistically different from 0
(at a 90 percent confidence level), then the table fails. Dividing the standard error by the estimate
yields the coefficient of variation (CV) for each estimate. (If the estimate is 0, a CV of 100 percent
is assigned.) To implement this requirement for each table at a given geographic area, CVs are cal-
culated for each table’s estimates, and the median CV value is determined. If the median CV value
for the table is less than or equal to 61 percent, the table passes for that geographic area and is
published; if it is greater than 61 percent, the table fails and is not published.
Whenever a table fails, a simpler table that collapses some of the detailed lines together can be
substituted for the original. If the simpler table passes, it is released. If it fails, none of the esti-
mates for that table and geographic area are released. These release rules are applied to single-
and multiyear period estimates based on 3 years of sample data. Current plans are not to apply
data release rules to the estimates based on 5 years of sample data.
Access the Data
To access the data within the MCDC data archive via Uexplore/Dexter go to the ACS section of the Uexplore/Dexter home page and follow the link to the desired vintage (e.g. follow the acs2014 link to access data based on 2014 vintage data). Here are those links (as of early 2017):