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Randomized Experimental Designs

Experimental criminology is a part of a larger and increasingly expanding scientific research evidence– based movement in social policy. In general terms, this movement is dedicated to the improvement of society through the utilization of the highest-quality scientific evidence on what works best (see, e.g. Sherman et al., 1997). The evidence-based movement first began in medicine and has, more recently, been embraced by the social sciences. Criminologists such as David Farrington, Lorraine Mazerolle, Anthony Petrosino, Lawrence Sherman, David Weisburd, and Brandon Welsh, and organizations such as the Academy of Experimental Criminology and the Campbell Collaboration’s Crime and Justice Group, have been leading advocates for the advancement of evidence-based crime control policy in general and the use of randomized experiments in criminology in particular.

In an evidence-based model, the source of scientific evidence is empirical research in the form of evaluations of programs, practices, and policies. Not all evaluation designs are considered equal, however. Some evaluation designs, such as randomized controlled experiments, are considered more scientifically valid than others. The findings of stronger evaluation designs are privileged over the findings of weaker research designs in determining “what works” in criminological interventions. For instance, in their report to the U.S. Congress on what works in preventing crime, University of Maryland researchers developed the Maryland Scientific Methods Scale to indicate to scholars, practitioners, and policymakers that studies evaluating criminological interventions may differ in terms of methodological quality of evaluation techniques (Sherman et al., 1997). Randomized experiments are considered the gold standard in evaluating the effects of criminological interventions on outcomes of interest such as crime rates and recidivism.