American Community Survey

Several of the ACS PUMS files have been reissued since their initial release. Below is a list of each file that was reissued with the date of reissue and a brief description.

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Public Use Microdata Sample files from the American Community Survey show the full range of population and housing unit responses collected on individual ACS questionnaires. For example, they show how respondents answered questions on occupation, place of work, and so forth. The PUMS files contain records for a subsample of ACS housing units and group quarters persons, with information on the characteristics of these housing units and group quarters persons plus the people in the selected housing units.

The records contain information from the completed ACS questionnaires for most questions for the selected subsample of housing units and group quarters persons. The questionnaire includes questions on age, sex, tenure, income, education, language spoken at home, journey to work, occupation, condominium status, shelter costs, vehicles available, and other subjects. See Subjects in the American Community Survey PUMS datasets in PUMS documentation.

As required by federal law, the confidentiality of ACS respondents is protected through a variety of steps to disguise or suppress original data while making sure the results are still useful. The first means of protecting is the suppression of all personal identification, such as name and address, from each record. In addition, a small number of records are switched with similar records from a neighboring area or receive another collection of characteristics developed by using a modeling technique. Age perturbation is one example of procedures that disguise original data by randomly adjusting the reported ages for a subset of individuals. The answers to open-ended questions, where an extreme value might identify an individual, are top-coded. Top coded questions include age, income, and housing unit value. In addition to modifying the individual records, respondents' confidentiality is protected because only large geographic areas are identified in the PUMS.

With the responses given in these files, you design tabulations to aggregate the responses in ways that are useful to you.

PUMS files are available for 1-year, 3-year, and 5-year estimate versions through the American Fact Finder (AFF). For help on deciding whether to use the 1-year, 3-year or 5-year version, see When to use 1-year, 3-year or 5-year estimates in Guidance for Data Users. Unless otherwise stated, PUMS or ACS microdata refer to the 1-year, 3-year or 5-year versions.

The ACS summary data are predefined tabulations of characteristics. The basic unit of analysis is a specific geographic entity -- state, county, etc. -- for which estimates of persons, families, households, or housing units in particular categories are provided.

With microdata, it is the user who determines the structure of the tabulation and the characteristic(s) to be tabulated.

In the ACS microdata, the basic unit is an individual housing unit, a group quarters person or persons who live in the selected housing unit. Each record shows most of the information associated with a specific housing unit or individual except for personal identifying information and some things that could be used to identify an individual. For more details of steps taken to protect the identity of respondents, please see the “About the ACS Public Use Microdata Sample File (PUMS)” section.

For many data users, the summary tables and tabular and narrative profile reports will suffice. Microdata are for those users who want to create do-it-yourself tabulations, to be able to further draw on the richness of detail recorded in the ACS.

PUMS estimates for selected housing and population characteristics are provided to assist data users in determining that they are correctly using the weights to compute estimates. These estimates are referred to as PUMS Estimates for User Verification. Data users who have doubts about the way they are computing estimates should attempt to reproduce the estimates that are provided in the Verification Files availabe in PUMS documentation.

Starting with 2006 files, we provide the standard error and the 90 percent margin of error for these verification estimates, which are calculated using the replicate weight method. For more information about the replicate weight method for calculating standard errors and the 90 percent margin of error, see the Accuracy of the PUMS in PUMS documentation.

Two resources are available to help PUMS users: “What PUMS Data Users Need to Know” handbook and “Introduction to the PUMS From the ACS” presentation.

Microdata users frequently want to look at relationships among variables not shown in the standard products offered by the Census Bureau. The advantage of PUMS is that data users can tabulate data according to the characteristics they want or need to know about. For example, what are the characteristics of unemployed homeowners? What characteristics do families with four or more children have in common?

PUMS files are perfect for people, such as students, who are looking for greater accessibility to inexpensive data for research projects. Data users in academic life -- economists, psychologists, and sociologists -- have found the PUMS useful for regression analysis and modeling applications.

Starting with the 2005 PUMS, the number of housing unit records contained in a 1-year PUMS file is about one percent of the total in the nation or approximately 1.3 million housing unit records and about 3 million person records. The 3-year PUMS files contain records for about three percent of housing units or about three times as many housing units and person records as the 1-year files. Similarly, the 5-year PUMS files contain about five times as many housing unit and person records as the 1-year files. Starting with the 2006 PUMS, the number of group quarters person records contained in a 1-year PUMS file is about one percent of the total population living in group quarters or about 81,000 records. The 2005-2007 3-year PUMS files, contains only about two times as many because there was no group quarters sample in the 2005 ACS. For the same reason, the 2005-2009 5-year PUMS files contain only about four times as many group quarter persons as the 1-year PUMS files. Subsequent 3-year PUMS files, and 5-year PUMS files will contain records for about three and five times, respectively, as many as the 1-year file.

For the housing unit population, there are two basic record types: the housing unit record and the person record. Each record has a unique identifier, i.e. a serial number that links the person to their proper housing unit. Each GQ person has two basic record types as well. The first is the person record and the other is pseudo-housing unit record, i.e., a "placeholder" record. All of a GQ person's data are included in their person record except the food stamp variables, which are the only data included in their "placeholder" record. A GQ person's "placeholder" record has zero housing unit weights so it is not counted in housing unit estimates. For more about the different record types, see the Accuracy of the PUMS in PUMS documentation.

The Census Bureau releases the PUMS in this format because of the tremendous amount of data contained in one record. Although these records are extremely large, they can be handled by most statistical or report-writing software. Each record has an individual weight, which allows users to produce population estimates close to those in other products showing sample data. Each record also includes replicate weights that are used to produce standard errors and to do statistical testing. For more information on using the replicate weights to calculate standard errors or the 90 percent margins of error, see the Accuracy of the PUMS in PUMS documentation.