"This report presents newly developed national estimates of arrests and arrest rates covering the 30-year period from 1980 to 2009, based on data from the FBI's Uniform Crime Reporting Program (UCR). By reviewing trends over the 30 years, readers can develop a detailed understanding of matters entering the criminal justice system in the U.S. through arrest. […] To interpret the arrest statistics presented in the report, readers are encouraged to review the FBI's counting rules discussed in the Methodology. This report uses arrest rates rather than arrest counts to display 30-year trends, because rates control for changes in the size of the reference population over this time period. In addition, readers should review graph legends before studying the graphs because some arrest rates have been multiplied by a constant to make the trends more visible."
National Criminal Justice Reference Service (U.S.): https://www.ncjrs.gov/