The information about the federal enforcement of the criminal laws by the INS 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.

• INS 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 INS 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 drawn from other areas on this site, sources for which are discussed below.
  
  
• National Profile and Enforcement Trends Over Time
  Data on aliens deported, inadmissables, and voluntary departures under docket control came from INS internal sources. Historical staffing information about the INS was obtained from the Office of Personnel Management. Data sources on criminal enforcement are discussed at more length below in the section on district enforcement.
  
  
• 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. INS internal sources were not used. Available INS data on criminal enforcement actions are quite cursory in nature, and TRAC has uncovered major questions regarding their reliability and validity. For example, INS figures for criminal prosecutions and convictions resulting from their investigations are substantially smaller than counts based upon federal prosecutor records of referrals received from INS, or court records on immigration cases.

  Coverage includes all referrals recommending criminal prosecution recorded as received by federal prosecutors where the Immigration and Naturalization 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.

  INS 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.