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, 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, on the selected subsample of housing units and group quarter persons, captured in their completed ACS questionnaires. 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.

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

The ACS summary data are predefined cross 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 characteristics to be tabulated.

In the ACS microdata, the basic unit is an individual housing unit or a group quarters person and the people who live in the selected housing unit are also available. Each record shows all the information associated with a specific housing unit or individual except for names, addresses, or other 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 incomes, 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 survey.

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. In addition, starting in 2006, we have added the standard error and the 90 percent margin of error based on replicate weights.

Tabulated 2007 PUMS Estimates for User Verification:

• PUMS estimates (SAS v8+ dataset)
• PUMS estimates (.lst text format)
• PUMS estimates (.csv format)

Note that some of these estimates may be different from the estimates for the same characteristics published in the American FactFinder. For an explanation of these differences, see the 2007 Accuracy of the PUMS document.

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? What kinds of Hispanic families in a state own their own homes?

The advantage of PUMS is that data users can tabulate data according to the characteristics they 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

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 persons to their proper housing unit. For the group quarters population, there are these two basic record types as well, but there are differences in the information provided on them. This is particularly true for the housing unit record type. For an explanation of these differences, see the 2007 Accuracy of the PUMS document.

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.