As required by federal law, the confidentiality of ACS respondents is protected through a variety of means, ensuring that it is impossible to identify individuals who provide any response, yet making sure the results are still useful.
The first means of protecting confidentiality is the removal 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, such as age, income, or housing unit value--where an extreme value might identify an individual--are top-coded. Top coding is the process of taking any response exceeding a particular value and replacing it with a predetermined value.
The Census Bureau also protects confidentiality by limiting the geographic area codes available on the PUMS files. The only geographic codes available in the PUMS records are those for regions, divisions, states, and Public Use Microdata Area or "PUMAs."
With the responses given in these files, you design tabulations to aggregate the responses in ways that are useful to you.