Format of PUMS Files
For the housing unit population, there are two basic record types:
Each record has a unique identifier, i.e., a serial number that links the person to their proper housing unit.
The group quarters population (whether sampled or imputed) has two basic record types as well:
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. Learn more about different record types in the Accuracy of the 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, view the Accuracy of the PUMS documentation.
Number of Housing Unit 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 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.
Number of Group Quarters RecordsThere was no group quarters sample in the 2005 ACS. The group quarters sample was added to the ACS in 2006.
From the 2006 PUMS to the 2010 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 ACS 3-year PUMS files contains only about two times as many records as the 1-year file. For the same reason, the 2005-2009 ACS 5-year PUMS files contain only about four times as many group quarter persons as the ACS 1-year PUMS files.
The ACS 3-year PUMS files (2006-2008, 2007-2009, and 2008-2010) and the 2006-2010 ACS 5-year PUMS file contain records for about three and five times, respectively, as many group quarters persons as the ACS 1-year file.
Starting with the 2011 ACS PUMS, the number of group quarters person records roughly doubled to represent about two percent of the total population. Subsequent PUMS files will contain the larger proportion of the group quarters population. Learn more about Group Quarters Small Area Estimation.