Beginning in January 2011, the Census Bureau incorporated additional safeguards in the Current Population Survey (CPS) public use files to ensure that respondent identifying information is not disclosed. In general, respondents' ages were altered, or "perturbed", in the public use microdata files to further protect the confidentiality of survey respondents and the data they supply. One result of the measures taken to enhance data confidentiality is that labor force and other estimates from the public use microdata files will no longer exactly match most estimates published by BLS, which are based on internal, nonpublic-use files. Although certain topside labor force estimates for all persons will continue to match published data--such as the overall levels of employed, unemployed, and not in the labor force--estimates below the topside level (such as employment status by age, sex, race, and ethnicity) all have the chance of differing slightly from the published data.
In addition, estimates calculated using characteristics such as industry, occupation, hours worked, duration of unemployment, along with all other characteristics not expressly listed above, are subject to such differences. All such differences should fall well within the sampling variability associated with CPS estimates.