Documentation: ACS 2008 -- 2010 (3-Year Estimates)
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Publisher: U.S. Census Bureau
Document: ACS 2010 3-Year Summary File: Technical Documentation
citation:
Social Explorer; U.S. Census Bureau; American Community Survey 2008-2010 Summary File: Technical Documentation.
ACS 2010 3-Year Summary File: Technical Documentation
Chapter 1. Introduction
1.1. The American Community Survey
The American Community Survey (ACS) is a household survey conducted by the U.S. Census Bureau that currently has an annual sample size of about 3.5 million addresses. The ACS data provides communities with the current information they need to plan investments and services. Information from the survey generates data that help determine how more than $400 billion in federal and state funds are distributed annually. Each year the survey produces data that cover the periods of 1-year, 3-year, and 5-year estimates for geographic areas in the United States and Puerto Rico, ranging from neighborhoods to Congressional districts to the entire nation. For more information about the ACS, please visit www.census.gov. ACS tables are published on the Census Bureau's American FactFinder (AFF) website, factfinder2.census.gov, and are available for download in several forms. This document will brief data users on the contents of the ACS Summary File and explain how they can use it to obtain the 3-year estimates.

1.2. The American Community Survey Summary File
The American Community Survey Summary File (ACSSF) is a unique data product that includes all the estimates and margins of error from the Detailed Tables and geographies that are published for the ACS. Other ACS data products such as Subject Tables and Data Profiles are created from the Detailed Tables and are therefore not available in the Summary File.Since the Detailed Tables contain a large number of cells, the tables are stored in a series of files with only the data from the tables, without such information as the title of the tables, the description of the rows, and the names of the geographic areas. That information is in other files that the user must merge with the data files to reproduce the tables.

The ACS Summary File data files are in American Standard Code for Information Interchange (ASCII) format. The files are divided into three types:
  • Geographies - (position based and comma delimited)
  • Estimates - (comma delimited)
  • Margins of Error - (comma delimited)
Chapter 2 discusses each component in detail and explains how to put them all together.

1.3. Topics and Geographies Covered
Data contained in the ACS Summary File cover demographic, social, economic, and housing subject areas. All Detailed Tables for the ACS 1-year estimates are in the Summary File and are listed in Appendix E.The published ACS Summary File geographies cover areas that are based on "summary levels". A summary level specifies the content and the hierarchical relationships of the geographic elements that are required to tabulate and summarize data. For example, summary level code "040" represents the U.S. States, Washington D.C., and Puerto Rico; while summary level code "050" represents counties and county equivalents within states.In addition to the summary level concept, the ACS 3-year estimates are published for areas that have passed the required 65,000 population threshold.Many resources are available to help users understand the ACS geographic terms and concepts. For additional nformation, please visit www.census.gov/geo/reference/index.html and www.census.gov/acs/www/guidance_for_data_users/geography/.

Users may also find the full list of summary levels published for the 1-year Detailed Tables in Appendix F.

1.4. Tools for Obtaining Data
Since using the ACS Summary File can be challenging, users should first check if their tables of interest are available for download on American FactFinder. Below are some other options to help users retrieve the tables they want. They are listed in order based on ease of use.

  • Summary File Excel Retrieval Tool
The Summary File Excel Retrieval Tool is a macro-driven Excel spreadsheet that provides a method to easily retrieve a table for the nation, states, and all of the geographic areas in a state (or for all cross-state geographic areas such as metropolitan statistical areas or census regions). This tool is designed to be easy to use, and does not require any programming experience. There is a drop down menu from which the user can select the state for the table and receive data for all geographies within the state. One key requirement is that Microsoft Excel 2007 or later is needed. Other hardware and software requirements for the tool are listed in Chapter 3.1. For more information about the application, visit the ACS Summary File page at http://www.census.gov/acs/www/data_documentation/summary_file/.

  • Summary File Excel Import Tool
The Summary File Excel Import Tool is a replicate of the Excel templates that Census 2000 provided for the SF3 summary file release. The Excel Import Tool provides a basic layout of each sequence in Excel in the same format as the estimate and margin of error files are formatted. For individuals that do not have Excel 2007 or later and are unable to use the Excel Retrieval Tool, the Excel Import Tool provides an alternative option to read the summary file into Excel. For more information on this tool, see Chapter 3.3.

  • SAS Programs
There are two programming options for SAS users. The first option is a set of individual SAS programs, one for each summary file by geography and sequence. These programs are best for users only interested in looking at a specific sequence for a specific geography. The second option is a single SAS program that is parameterized to allow users to read in any sequence for any geography into SAS. This program can also be used to read the entire summary file into SAS, and is designed for users looking for a large amount of data. For more information on these programs, see Chapter 3.1.

1.5. Notable Changes to the Summary File
The files for the 2008-2010 ACS 3-year estimates are similar to last year's publications (the 2009 ACS 1-, 3-, and 5-year estimates) with the following exceptions. These changes were established starting with the 2010 ACS 3-year release:

  • Geography Files Offered in Comma Delimited Format
The geography files are offered in two formats: position based and comma delimited. In previous years, the geography files were only offered in position based format.
  • SummaryFileXLS.zip Renamed to SummaryFileTemplates.zip
The zipped "SummaryFileXLS" folder was renamed to "SummaryFileTemplates" to more accurately reflect its contents: templates (or column headers) for each of the sequence files. This folder is located in the "User Tools" folder on the Summary File site: http://www2.census.gov/acs2010_3yr/summaryfile/UserTools/.
  • SummaryFileTemplates.zip Includes a Template for the Geography File

A template for the geography file was added in the "SummaryFileTemplates" zipped folder due to popular demand. For more information, visit Chapter 2.4.
  • Missing Value Has Been Changed From Dot to Empty Cell
Previously, a dot "." was used to indicate that an estimate was unavailable due to coefficient of variation (CV) filtering or Disclosure Review Board (DRB) restrictions. For the 2010 ACS Summary Files, the dot is being replaced by an empty cell. For more information, visit Appendix C.3.

  • Instructions Added on How to Join the Summary File to TIGER/Line Shapefiles
The Summary File Technical Documentation now includes instructions on how to join the ACSSF to TIGER/Line Shapefiles. For more information, visit Chapter 2.6.

1.6. Contact Us
Please send any technical questions or comments on the ACS Summary File you have via email to: acso.users.support@census.gov. If you have questions or comments about the American Community Survey, you can submit a question online at http://ask.census.gov/.