this chapter summarizes the major findings of the original research reported in this book. The literature on police use of force has developed enormously over the years and draws on a variety of data sources, although it relies mainly on official agency records and observational studies. Each of these methods has its limitations. First, many agencies do not collect use-of-force information. Second, if the data are collected, they are often created by the officers who were involved in the action, which may bias the information. Third, the data are not uniform across agencies. Fourth, many agencies that collect information do not grant access to outside researchers. For these and other reasons we discuss, the study of police use of force is fraught with problems. Of course, other data can be used to examine an agency's use of force, including lawsuits, citizen complaints, and observational techniques, but, as we have seen, each of these methods also has its own shortcomings.

Agencies that collect and maintain use-of-force data may only require them for specific types and/or high levels of force, and not for the full range of cases. For example, one agency may only require reports for incidents when an intermediate weapon is used, while another may have officers complete specialized forms for all force used beyond handcuffing and come-along holds. Making comparisons across agencies is therefore problematic and must be undertaken with caution.