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The American Community Survey

Rev. Nov. 5, 2013
General Info   |  Data Release Plan   |  Access Data   |  What to Expect   |   ACS Data Profiles
PUMS Data   |  PUMAs   |   CPR Method   |   More Information / Things to Know

General Information

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:

Suppressing Tables

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 (and extensive metadata) within the MCDC data archive go to the ACS section of the Uexplore/Dexter home page.

Prior to the 2005 survey year the only data available from the ACS are for selected geographic areas with a minimum of 250,000 population. Beginning with 2005 data there are data for geographic areas of 65,000+ population. These data (as well as the later data available on our site) can be accessed via the Census Bureau's American FactFinder web application. For the MCDC online data archive we began downloading and converting ACS data starting with the 2005 results (released in 2006). We are providing access to the ACS summary data (base tables, profiles and our own custom extracts -- all but the PUMS data, which are stored separately -- see below) for each year in these uexplore-able data directories:

Note: If you do not see the latest year you are looking for check the ACS section of the Uexplore/Dexter home page.
acs2012 acs2011 acs2010 acs2009 acs2008 acs2007 acs2006 acs2005

The acs directory is generic (i.e. not time or data product specific) and contains a number of interesting documents. The Readme file/web page you are currently reading is contained in this directory.

The MCDC has created a series of xsamples mini tutorials that demonstrate how to access data in the archive. Several of these pertain to the ACS data, including our most recent xsamples module, acsBasetbls, which combines frames-based access to a collection of input and output modules with links to video modules that show and tell how the extraction works.

What To Expect (Coming Soon)

This Year (2013)

There will be the usual 3 sets of estimates released this year, starting with the single-year data for large areas in September. The specific dates per the Census Bureau Events Calendar (revised following government shutdown in late October) are:

  • Sept. 19: Single-year estimates for 2012.

  • Nov. 14: Three-year period estimates for 2010-2012.

  • Dec. 17: Five-year period estimates for 2008-2012.

ACS Data Profiles and the ACS Extract Assistant

Both the Census Bureau and the Missouri Census Data Center provide data profile reports (and corresponding data files) containing highlights of the very detailed information contained in the complete set of base tables. The Bureau profiles can be accessed via American FactFinder. Access to the MCDC's acsporifle application stypically starts by access the ACS Profile Menu page (this link is currently featured at the top of the MCDC's Quick Links box, which appears on most MCDC web pages. The closely-related ACS Trends report can be accessed from a main menu page that also appears in the Quick Links box, or you can access it as a link from the acsprofiles report page. For users who prefer to access their data in machine-readable formats (for 5-year estimates only, currently) and for all-available geographic areas of a type (e.g. all counties in the U.S. or in a selected state) there is a custom Dexter front end application - American Community Survey Standard Profile Extract Assistant that will assist you in building a dexter query form that will select just the data you need. It comes with a video-based tutorial (linked to at the top of the application page) that shows you how it works.


The ACS also includes a public use microdata sample (PUMS) product. We plan to keep all such datasets (regardless of year) in the acspums data directory. We currently have data for 2004 thru 2011 . 2012-vintage PUMS data are expected as follows:

  1. 1-year data on Nov. 14, 2013
  2. 3-year data on Feb. 6, 2014
  3. 5-year data on March 6, 2014.
This collection will only be of direct interest to researchers with access to and knowledge of how to use a statistical software package. For a more detailed discussion see the ACS PUMS item from our "Ten More Things to Know..." web page, linked to in the Where to Get More Information section, below.

PUMAs (Public Use Microdata Areas) Related to ACS

Users of this web site will notice that we place considerable emphasis on data summarized at the PUMA geographic level. This is because PUMAs are large enough (100,000 minimum population) that they qualify to have new single-year ACS data published each year. We can use PUMA data therefore to look at trends and maps that cover the entire state. We have created custom reports to help users understand where these PUMAs are (what counties and cities they contain or in which they are contained) together with links to pdf map files showing them (see our Geographic Reference Reports, the first 3 bullets). To learn more see the discussion of PUMAs that appears in our introductory Ten Things to Know About the American Community Survey page (cited just below).

CPR: Experimental Method For Estimating Data for Smaller Counties

The MCDC has experimented with a methodology for estimating county level ACS data using a County to PUMA Ratio methodology. If interested, try viewing Introduction to the County-PUMA Ratio Method and the related Time Promoting Using CPR Methodology pages. We welcome user feedback on these topics as we weigh the value of pursuing such approaches to enhancing the ACS data products.

Where to Get More Information

There has been and continues to be a lot written about the ACS. Here are some of our favorite resources.

  • American Community Survey Home Page at the Census Bureau. This is the official site. Comprehensive, with many links to the various components. From it (under the "About the ACS" tab) you'll find a link to the current (2010) ACS Questionnaire (pdf file).

  • American Community Survey Geography page showing which geographic levels are getting 1-year, 3-year and 5-year estimates (for recent and one future data cycle). This is where you can find out (for example) when to expect data for 113th Congressional Districts, or when we started getting data by 2010 census tracts instead of 2000 tracts. You can also find Release Notes regarding any anomalies in the data, such as the situation in 3 New York counties where they modified some tract boundaries starting with the 2011 release. This page contains a link to Geography and the American Community Survey, which is the ultimate source for the topic.

  • 2011 Data Release contains information specific to the 2011 vintage data release (completed in December, 2012). The schedule for the 2012 vintage data has not yet been released. (But check the 2011 page to see if this has changed, in which case there will be a link to it.)

  • The ACS Compass Products page at the Bureau's ACS web site provides links to a series of educational materials related to the ACS. Includes handbooks, power point tutorials and other materials, which seem to be appearing almost every few weeks. The Compass Handbooks are all targeted to specific audiences and have titles such as What General Data Users Need to Know, What the Business Community Needs to Know, etc.

  • Stats Indiana ACS Page has some nice ACS data and links. For example, it contains the following link for estimimating MOE's of calculated values.

  • Online ACS Calculator at Cornell University provides a quick and easy way to calculate MOE's and do signficance-of-difference tests by simply entering the relevant estimate and MOE values, and letting it do the calculations. The formulas used are the ones published in the Bureau's Compass guides and are known to be less than perfect. Nevertheless... To get the MOE for a percentage you enter the values for the numerator in the Value1 boxes, and of the denominator in the Value2 boxes; then select Proportion as the Operation and read the answer in the Result box.

  • Ten Things to Know About the American Community Survey is a locally produced introductory document that focuses on things that new users will need to know in order to make use of this important data resource. (Parts are specific to the 2005 edition of the data.) Created in April, 2007.

  • Ten More Things to Know (and Do) About the American Community Survey is a locally produced document that is obviously a sequel to the previous item. This document (which is actually three separate web pages linked together) is considerably longer and more detailed than its predecessor, with lots of screenshots and specific examples of how to access the data. Created in early 2010.

  • The American Community Survey vs. the Decennial Census Long Form is an essay that considers the question "Are we better off now [6/2009] than we were a decade ago?" following the Big Trade involving giving up the decennial census long form in exchange for the ACS.

  • The ACS Section of MCDCs Product Inventory Showcase points to various data products/applications on this (MCDC) web site related to the ACS.

  • Population Bulletin on The American Community Survey from the Population Reference Bureau is an excellent in-depth review of the survey (written in September, 2005) . This is a 20-page pdf document.

  • Map of Missouri by County (pdf file) showing the three population categories (<20K, 20K to < 65K and 65K+) relevant to ACS data products. Also displays the PUMA boundaries and labels. (Because sometimes you can use PUMA level data as the next best thing when county level is not available.)

  • The Docs subdirectory of the MCDC's (this) acs data directory has some useful links.

You can subscribe to the "ACS Alerts" mailing list so that you will be notified of the latest news about the ACS. See the ACS Alerts web page for more information. The alerts are also posted to the ACS web site.

URL: http://mcdc.missouri.edu/data/acs/Readme.shtml

This file last modified Wednesday December 18, 2013, 12:24:15

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