The information about the DHS, its staffing and criminal enforcement efforts, was compiled by TRAC from a variety of sources. The sources included computerized data obtained under the Freedom of Information Act from the Justice Department and from the United States Office of Personnel Management. These data were supplemented by interviews with current and former government officials, attorneys, and agency data processing specialists.

Additional information was drawn from internal administrative records, electronic and hardcover publications of the Department of Homeland Security and the former Immigration and Naturalization and Customs Services; internal administrative records and statistical reports of the Justice Department; electronic databases, internal records and hardcover publications of the Administrative Office of the United States Courts and the U.S. Sentencing Commission; internal records, electronic and hardcover reports of the Office of Personnel Management; internal records, electronic and hardcover reports of the General Accounting Office, the Congressional Authorization & Budget Submissions; reports by the White House Office of National Drug Control Policy as well as Congressional hearings. Basic population figures came from the United States Census Bureau.

This section on "About the Data" provides information about the following topics. Choose from the following links for further details on each of these topical areas.

  Data Sources and Coverage: details on specific data sources used on this site

  Judging the Quality of Government Data: general information about how to judge the quality of government statistics, and what steps TRAC uses to assess the quality of data it receives.

  Understanding the Terminology which Agencies Use: specialized terminology used by these agency sources in categorizing their activities.