Why don't the American Community Survey (ACS) Public Use Microdata Sample (PUMS) file estimates match data.census.gov estimates?

Estimates generated using the American Community Survey (ACS) Public Use Microdata Sample (PUMS) files will be slightly different from the pretabulated ACS estimates in data.census.gov because PUMS data:

• Include only about two-thirds of the cases used to create estimates on data.census.gov.
• Contain additional edits and modifications like "top-coding" of continuous variables with outlying values (such as income or transportation time) and the reduction of category availability for variables with hundreds of categories (such as ancestry or birthplace).

These measures and more are taken to protect the confidentiality of the PUMS data. For more information about PUMS confidentiality measures visit Section 1 of the Understanding and Using the ACS PUMS Files handbook. Further PUMS information and documentation is available on the Public Use Microdata Sample webpage.