U.S. Census Bureau, American Community Survey 2008 Summary File: Technical Documentation.

1) Details on changes in the detailed tables and derived products since the 2006 ACS, including new products, is available on the ACS Website at: http://www.census.gov/acs/www/Products/2008/prodchanges.html

2) Changes to the 2008 detailed tables which contain complete lists of new, removed, and modified tables can be referenced on the ACS Website on: http://www.census.gov/acs/www/Downloads/Table_Changes2008.xls

3) Because of added/dropped tables, changes were made to some of the tables in the sequences. Sequences 51 and 146 contain geo-restricted tables, so there are many missing tables in these sequences. Sequences 125-133 contain 3 new large median tables (these tables contain 499 cells). Due to the size restriction on the sequences (no more than 245 cells), each of the tables was broken into 3 sequences. For example, sequence 125 contains B24121 cells 1-167, sequence 126 contains B24121 cells 168-333, and sequence 127 contains B24121 cells 334-499. For more details, see Chapter 5 and review the file http://www2.census.gov/acs2008_1yr/summaryfile/merge_5_6_final.xls

4) ACS 2008 detailed tables that were subject to geographic restrictions are located on: http://www.census.gov/acs/www/Products/users_guide/ACS2008_Data_Product_Geographic_Restriction.xls

5) Each set of ACS Summary file Technical Documentation is tied to a specific ACS year. Currently we have five sets of ACS Summary file, 2005 (prototype), 2006 (prototype), 2006 (production), 2008 (production), and 2008 (production).

6) The ACS 2006 and ACS 2007 Production Summary files were created using the same file naming convention based on user input. For more details reference Chapter 1 of the technical documentation, section 3.3: File Identification.

Summary statistics.

The American Community Survey (ACS) is the largest household survey in the United States, with an annual sample size of about 3 million addresses. Every year the ACS supports the release of single-year estimates for geographic areas with populations of 65,000 or more.

This release of the American Community Survey Production Summary file (ACS-SF) contains the 2008 detailed tables (a.k.a. "base tables"). Please send any comments you have via email to: nicholas.m.spanos@census.gov. We will keep users aware of any updates via the ACS Alert from the ACS website.

The 2006, 2008, and 2008 data products include the Group Quarters (GQ) population. The GQ population includes all people not living in households. ACS data were collected from residents who were currently residing in the GQs when the ACS was conducted at that location. Data are collected at two types of group quarters: institutional, including residences such as correctional facilities, nursing homes, and psychiatric hospitals; and non-institutional, which include residences such as college dormitories, military barracks, group homes, and shelters.

Every table that should be a "total population" table will include the GQ population. But, tables describing household characteristics will not include GQ data. For example, tables such as Median Household Income, will only have data from the population living in households.

The ACS-SF contains sample data, which is information about the characteristics of local communities compiled from the questions asked of a sample of people and housing units. The ACS covers a broad spectrum of geographic areas in the United States and Puerto Rico. The topics listed below are covered by the ACS and focus on demographic, social, housing, and economic characteristics.

Demographic:
Sex	Age
Households by type	Race
Relationship	Hispanic origin
Social:
School enrollment	Educational attainment
Fertility	Residence one year ago
Veteran status	Disability status
U.S. citizenship status	Language spoken at home
Martial status	Place of birth
Year of entry	Ancestry
Grandparents caring for children	World region of birth of foreign born
Economic:
Employment status	Commuting to work
Class of worker	Income and benefits
Industry	Occupation
Poverty status
Housing:
Housing occupancy	Housing tenure
Units in structure	Year structure built
Number of rooms	Number of bedrooms
House heating fuel	Housing value
Occupants per room	Vehicles available
Mortgage status and costs	Utility cost
Year householder moved into unit	Gross rent

The Census Bureau uses the data collected by the ACS to create estimates and variances, which are termed statistics, for these characteristics. The statistics produced from the ACS describe the characteristics of population and housing in the United States and Puerto Rico. The ACS releases statistics in several forms - totals, proportions, percentages, means, medians, averages, and ratios. There are three sets of data files in identical format with one field per estimate. One file contains the estimates, the second file contains the standard errors, and the third file contains the margin of error.

The ACS-SF contains a total of 1374 unique detailed tables. Of these tables, ID's beginning with the letter "C" are collapsed versions of tables (i.e. these tables have fewer detailed cells). These detailed tables include both U.S. and Puerto Rico population and housing characteristics for the housing unit population and for a limited list of race and Hispanic or Latino groups. Population and housing items may be cross tabulated. Selected aggregates and medians are also provided. A complete listing of subjects in this file is found in the section, "Subject Locator."

The ACS Production Summary file includes all detailed tables for all geographic areas published by the 2008 ACS. The main directory of the ACS-Summary File's FTP server (http://www2.census.gov/acs2008_1yr/summaryfile/) contains documentation on using the ACS-SF and 53 subdirectories, for the United States, the 50 states, the District of Columbia, and Puerto Rico. The file structures are identical for all files, but the geographic coverage differs.

This abstract lists the most frequently accessed geographic levels. The "Summary Level Sequence Chart" section outlines the hierarchical and inventory geographic summaries in their entirety. Two summary level sequence charts are provided: one for the state files and one for the final national file.

A brief summary of the chapters in the documentation is listed below:

1. Chapter 1: Abstract contains an overview of the American Community Survey (ACS) and how to use the ACS Summary File technical documentation.
2. Chapter 2: How to Use the Summary File gives users the background information on the data tables. It also describes the naming conventions on the table names, and it gives a brief summary of the geographies.
3. Chapter 3: Subject Locator is an index designed to help users quickly identify the tables in the summary file. This index is arranged in alphabetical order by the name of a subject.
4. Chapter 4: Summary Level Sequence Chart has a detailed list on the geographies and their summary level. The summary level is a three-character code that the ACS uses for identifications on geographies. The summary level is used in the production of the ACS data.
5. Chapter 5: List of Detailed Tables contains information on the file identification, the tables identification number, title of the table, how many cells are the table, the start position for the table, and the sequence numbers.
6. Chapter 6: Accuracy of the Data provides data users with a basic understanding of the sample design, estimation methodology, and accuracy of the data.
7. Chapter 7: User Updates informs data users about corrections, errata, and related information. Users can find unique characteristics, changes, or corrections associated with the data. American Community Survey Notes and Errata, which contain user updates for individual files, are located on http://www.census.gov/acs/www/UseData/Errata.htm

Additional reference materials can be found in the appendices of this document:

A. Appendix A contains information on American Community Survey geographic terms and concepts.
B. Appendix B links to the subject definitions on the ACS Website.
C. Appendix C gives an overview on American Community Surveys collection methods and procedures. Data Collection and Processing Procedures are located in Appendix C.
D. Appendix D links to the ACS questionnaire on the website.
E. Appendix E links to data products and user assistance.
F. Appendix F links to maps of areas published by the 2008 ACS for the "nation," "counties" and "places," "PUMAs," "Core Based Statistical Areas," and the "110th Congressional District."
G. Appendix G links to ACS code lists for "Ancestry," "Hispanic Origin," "Industry," "Language," "Occupation," "Place of Birth," "Migration," and "Place of Work," "Race," and "State." Also included is the GQ Code List.
H. Appendix H consists of the document "Examples of Standard Error Calculations" which contains examples based on the real data to demonstrate the use of the formulas referenced in the Accuracy of the Data Document in Chapter 7.
I. Appendix I links to FTP documentation, including the ReadMe file and sample SAS programs.
J. Additional User Notes are located in Appendix J.

The section on User Updates informs data users about corrections, errata, and related explanatory information. These updates provide information about unique characteristics, changes, or corrections. However, sometimes this information becomes available too late to be reflected in the tables or related documentation. American Community Survey user updates are available on the Census Bureau's Internet site at http://www.census.gov/acs/www/UseData/Errata.htm
Users also can register to receive user updates by e-mail by contacting Customer Services Center, Marketing Services Office, U.S. Census Bureau on 301-763-INFO (webmaster@census.gov).