American Community Survey (ACS)

ACS Public Use Microdata Sample File (PUMS)

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.

All identifying information, such as names and addresses, is removed to ensure confidentiality. The records contain information from the completed ACS questionnaires for the selected sample of housing units and group quarters persons. The questionnaire included questions on age, sex, tenure, income, education, language spoken at home, journey to work, occupation, condominium status, shelter costs, vehicles available, and other subjects. For more information click on the following link: Subjects in the American Community Survey PUMS datasets.

The full range of population and housing information collected in the American Community Survey is available in the PUMS. For most questions asked on the ACS questionnaire, the response is given in these files -- and you design tabulations to aggregate the responses in ways that are useful to you.

PUMS files are available in both 1-year estimate and 3-year estimate versions through the American Fact Finder (AFF). For help on deciding whether to use the 1-year or the 3-year version click on the following link: Using Multiyear Estimates. Unless otherwise stated, PUMS or ACS microdata refer to both the 1-year and the 3-year versions.

Summary Data and Microdata -- What's the Difference?

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 all the information associated with a specific housing unit or individual except for names, addresses, or other personal identifying information.

The Census Bureau uses a minimum population threshold to help avoid disclosure of information about any household or individual. Only large geographic areas are identified on microdata records -- in the case of the American Community Survey, the nation, states, and Public Use Microdata Areas (PUMAs).

To further protect confidentiality, there is limited detail on items such as place of residence, place of work, high income, and other items.

Why Use PUMS?

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.

Help With Using PUMS!

PUMS estimates for selected housing and population characteristics are included here 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 one of the following files. Starting with 2006, 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, see the Accuracy of the PUMS.

Who Can Use PUMS?

Microdata users frequently want to look at relationships among variables not shown in the standard products offered by the Census Bureau. For example, what are the characteristics of unemployed homeowners? What characteristics do families with four or more children have in common?

The advantage of PUMS is that data users can tabulate data according to the characteristics they want or need to know about.

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.

PUMS Records

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 records. The first 3-year PUMS file, for the period 2005-2007, contains records for about three percent of housing units or about three times as many as the 1-year file. 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 first 3-year PUMS file, for the period 2005-2007, contains only about two times as many because there was no group quarters sample in the 2005 ACS. Subsequent 3-year PUMS files will contain records for about three percent of the total population living in group quarters or three times 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 group quarters 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 group quarters 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 group quarters 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.

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, see the Accuracy of the PUMS.