This study reached two major conclusions: little reliable evidence exists showing that variation in the severity of punishment has a substantial deterrent effect, and that strong evidence exists indicating that variation in the certainty of punishment has a large deterrent effect, particularly with the use of specific programs that alter the use of police. The authors of this study conducted a literature review to assess the following claims: 1) the marginal deterrent effect of increasing already lengthy prison sentences is modest at best; 2) increasing the visibility of the police by hiring more officers or allocating existing officers in ways that heighten the perceived risk of apprehension seems to have substantial marginal deterrent effects; and 3) the experience of imprisonment compared with non-custodial sanctions does not seem to prevent reoffending, rather the effect appears to be criminogenic. The results of the review show that little guidance exists in the statistical literature on how police resources should be used to reduce crime and imprisonment rates. Policy and research recommendations are included. References