"The statistics of crime are known as the most unreliable and difficult of all statistics. First, the laws which define crimes change. Second, the number of crimes actually committed cannot possibly be enumerated. This is true of many of the major crimes and even more true of the minor crimes. Third, any record of crimes, such as arrests, convictions, or commitments to prison, can be sued as an index of crimes committed only on the assumption that this index maintains a constant ratio of crimes committed. The assumption is a large one, for the recorded crimes are affected by police policies, court policies, and public opinion."
(Source: Sutherland, E. (1947). Principles of criminology (4th ed.). Chicago: J.P. Lippincott. As cited in Mosher, J.C., Miethe. T.D., & Phillips, D. M. (2002). The mismeasure of crime. Thousand Oaks, CA: Sage Publications.)