Which correctional strategies, programs, policies, and interventions effectively reduce crime? That is the question addressed in this book. Obviously, other issues such as costs and justice are important in public policy decisions. However, the degree to which crime is reduced is always important, and, in the eyes of many, it is the primary reason for or goal of corrections. In this book, therefore, I focus solely on the effectiveness of these policies in reducing crime. The decision whether a particular strategy is effective is made on the basis of scientific evidence.

Although crime reduction is one of the major, if not the major, goal of correctional policy, the goals of sentencing are somewhat different. Traditionally, four major goals are attributed to sentencing: retribution, rehabilitation, deterrence, and incapacitation. Retribution refers to just desserts: the idea that people who engage in criminal behavior deserve to be punished. This is an important purpose of most sentences. The three other goals of sentencing are similar to those of corrections. These goals are utilitarian in purpose, emphasizing methods to protect the public and reduce crime. The three goals differ, however, in the mechanism expected to provide public safety. The first, deterrence, emphasizes the onerousness of punishment; offenders will be deterred from committing crimes as a result of a rational calculation that the costs of punishment are too great. From this perspective, the punishment is so repugnant that neither the punished offender (specific deterrence) nor others (general deterrence) will commit the crimes.