The study found that the treatment effect for low-risk offenders was a slight decrease in reoffending; however, the confidence interval showed a wide range between the upper and lower levels, suggesting that the effect size calculated for the low-risk group should be interpreted cautiously. An increase in reoffending was found for the moderate-risk groups, and the high-risk groups experienced a decrease in reoffending. Mixed-risk groups experienced an 18-percent increase in reoffending; however, the small sample size suggests these findings should be interpreted with caution. The types of treatment used in the 42 studies eligible for analysis were substance abuse treatment and modification of antisocial thinking and attitudes. Treatment modalities were group milieu, cognitive behavioral therapy, family therapy, and therapeutic communities. Treatment locations included institutions and the community. Treatment formats were groups sessions and individual sessions. Thirteen studies involved low-risk offenders, and 14 studies included offenders classified as moderate risk. Twelve studies involved high-risk samples, and 3 studies provided treatment for groups with mixed-risk offenders. An extensive literature search identified all possible research that focused on program evaluation and risk. The selected studies were then narrowed based on their inclusion of specific criteria. These criteria required that only quasi-experimental studies with clearly defined treatment and comparison groups from an offending population were eligible (n=42).