Criminal justice professionals and criminologists use many different kinds of evidence—quantitative, qualitative, historical, and legal—to answer the questions they pose. Most practitioners rely on methods derived from the social sciences to gather evidence: interviews, direct observation, surveys, narrative analysis, natural setting experiments, and analysis of demographic, statistical, legal, geographic, and historical data. Criminologists also use theory-based evidence or the history of a theory or law enforcement policy.

As a student, you will probably be required to use both primary and secondary sources as evidence and to gather and analyze both quantitative and qualitative data. Quantitative data may include crime statistics, incarceration rates, racial profiling data from police stops, ticketing rates, and data on crime statistics linked to geographic areas. Qualitative data may include your own observations, others’ responses to interviews and surveys, and the stories people tell about their encounters with crime and the criminal justice system.

Your instructors will also expect you to consult relevant secondary sources, including articles in scholarly and popular periodicals (such as Police Chief ), news media, government and legal documents, statistical reports, and organizational Web sites, reports, and studies.