The information about the federal enforcement of the criminal laws by the U.S. Customs Service and the Justice Department on this Web site comes from many sources. This is a guide to the major agency data sources that were used. It is organized by Web site area.

• Customs at Work
  This area draws upon a wide scope of information sources, including background information about the agency, its history and evolving responsibilities, as well as its activities. Key sources of information were Customs Service agency reports, congressional hearings, GAO reports, budget documents, federal court records, and interviews. Prior scholarly work on the agency was also examined. Specific figures reported are also drawn from other areas on this site, sources for which are discussed below.

• National Profile and Enforcement Trends Over Time
  Historical staffing information about the Customs Service was obtained from the Office of Personnel Management. The primary source for criminal enforcement figures is the federal prosecutor database compiled by TRAC from U.S. Justice Department case management data systems. Reports by the White House Office of National Drug Control Policy were also used to track budget allocations for drug interdiction and investigative activities. Context concerning federal drug enforcement more generally also relied upon reports from the Administrative Office of the U. S. Courts and the U.S. Sentencing Commission.

• District Enforcement Annual Layers
  The primary source for these figures is the federal prosecutor database compiled by TRAC from U.S. Justice Department case management data systems. Customs Service internal sources were not used. Inquiries to the agency to review TRAC's findings did not meet with any response from the Customs Service.

  Coverage includes all referrals recommending criminal prosecution recorded as received by federal prosecutors where the Customs Service is recorded by Justice as the lead investigative agency. All criminal enforcement figures are based upon number of individuals (defendants or potential defendants) involved -- rather than number of cases. A single referral or case filed in court may involve more than one individual. Each defendant involved is separately counted in these figures.

  Population figures used in computing per capita rates and ranks are county level annual estimates from the United States Census Bureau.

  Customs Service staff figures are based upon the number of individuals on the payroll at the end of the fiscal year by post-of-duty and were compiled by TRAC from Office of Personnel Management sources. Unless otherwise noted, the figures include only fulltime staff in each occupational series.