III. Systematic Reviews and Meta-Analytic Methods in Criminology
There is a consensus among those who advocate for evidence-based crime policy that systematic reviews are an important tool in this process. In systematic reviews, researchers attempt to gather relevant evaluative studies in a specific area (e.g., the impact of correctional boot camps on offending), critically appraise them, and come to judgments about what works “using explicit, transparent, state-of- the-art methods” (Petrosino, Boruch, Soydan, Duggan, & Sanchez-Meca, 2001, p. 21). Rigorous methods are used to summarize, analyze, and combine study findings. The Campbell Collaboration Crime and Justice Group, formed in 2000, aims to prepare and maintain systematic reviews of criminological interventions and to make them electronically accessible to scholars, practitioners, policymakers, and the general public (Farrington & Petrosino, 2001; see also http://www.campbellcollaboration.org/). The Crime and Justice Group requires reviewers of criminological interventions to select studies with high internal validity, such as randomized controlled trials and well-designed quasi-experiments with comparison groups (Farrington & Petrosino, 2001).
Meta-analysis is a method of systematic reviewing and was designed to synthesize empirical relationships across studies, such as the effects of a specific crime prevention intervention on criminal offending behavior (Wilson, 2001). Meta-analysis quantifies the direction and the magnitude of the findings of interest and uses specialized statistical methods to analyze the relationships between findings and study features (Lipsey &Wilson, 1993;Wilson, 2001). Although the methods are technical, meta-analysis provides a defensible strategy for summarizing the effects of crime prevention and intervention efforts for informing public policy (Wilson, 2001). For instance, Farrington and Welsh (2005) carried out a series of meta-analyses of criminological experiments of the last 20 years and concluded that prevention methods in general, and multisystemic therapy in particular, were effective in reducing offending. They also reported that correctional therapy, batterer treatment programs, drug courts, juvenile restitution, and police targeting of crime hot spots were effective. However, “Scared Straight” programs and boot camps for offenders were not effective at preventing crime.