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.
Randomized experiments have a relatively long history in criminology. The first randomized experiment conducted in criminology is commonly believed to be the Cambridge– Somerville Youth Study (Powers &Witmer, 1951):
Relatively few randomized experiments in criminology were conducted during the 1950s, 1960s, and 1970s (Weisburd et al., 2008). However, the number of randomized experiments in criminology started to rise in the mid- 1980s. In their influential book titled Understanding and Controlling Crime, Farrington, Ohlin, and Wilson (1986) recommended the use of randomized experiments whenever possible to test criminal justice interventions. This book generated considerable interest in experimentation among criminologists and, more important, at funding agencies such as the U.S. National Institute of Justice, which sponsored a series of randomized controlled experiments in the late 1980s. In their examination of randomized experiments on crime and justice, Farrington and Welsh (2006) found that experiments with a minimum of 100 participants more than doubled between 1957 and 1981, when there were 37, and between 1982 and 2004, when there were 85. Although randomized experiments in criminology are more common now compared with the 1980s, they continue to represent a small percentage of the total number of impact or outcome evaluations conducted in areas relevant to crime and justice each year (Weisburd et al., 2008).
This research paper begins by describing the key features of experimental, quasi-experimental, and nonexperimental research designs. The strengths of randomized experiments in determining cause and effect in criminology are assessed relative to these other commonly used research designs. Next, systematic reviews of existing evaluations and metaanalytic methods to synthesize the effectiveness of criminological interventions are discussed. These techniques represent important new features of the evidence-based policy movement in criminology. The research paper concludes by reviewing the critiques of experimentation in criminology and then presents a series of recommendations to overcome the ethical, political, and practical barriers to experimentation in crime and justice.