In the United States, we often base criminal justice policy on ideology, rather than research.  This sometimes results in time, effort, and money spent on crime prevention measures that are ineffective, or at best, untested.  Groups within the public sector, private sector, and academia are changing this by implementing evidence-based practices.  For example, in the private sector, the IAHSS Foundation began publishing an evidence-based research series in 2015. Similar endeavors were undertaken by the public sector and academia much earlier.

As the title implies, evidence comes in different varieties. The evidence hierarchy, below, dates back to 1979 with subsequent conceptual expansions in 1988 and 2000 when it reached its current form. The evidence hierarchy shows the value of various types of evidence, as explained by Criminologist Jerry Ratcliffe in a short video.

As Dr. Ratliffe explained, Meta-Analysis and Systematic Reviews are the highest form of evidence for policy decision-making. A Systematic Review is a detailed, systematic and transparent means of gathering, appraising and synthesizing evidence to answer a well-defined question.

As explained by Thomas Abt in Bleeding Out, “Originating in medicine, these reviews exhaustively gather and rigorously interpret the results of multiple evaluations. They set clear goals, use transparent methodologies, and focus only on the most reliable studies. Systematic reviews are now widely regarded as providing the strongest evidence of “what works” when evaluating programs and policies.”

A Meta-Analysis is a statistical procedure for combining numerical data from multiple separate studies and should only ever be conducted in the context of a systematic review. For more information, consider the evidence criteria developed by the Campbell Collaboration and the Maryland Scientific Methods Scale, and a book chapter entitled Improving the Evidence Base in Security: Systematic Reviews and Meta-Analysis.

For crime prevention evidence, specificity matters. One should consider whether the evidence on crime prevention applies to specific crime categories (violent crimes, property crimes, disorder crimes) or to multiple crime types. For example, video surveillance has “no effect” on violent crime, but “promising effects” on property crime.

In some cases, the research on a particular crime prevention measure may have different findings for specific crimes (e.g. robbery, burglary, etc.). For example, one Randomized Control Trial found that directed patrols (a tactic used by law enforcement agencies to try to reduce or stop crime in specific or problematic areas) resulted in a sizable decrease in non-domestic firearm assaults, but had no impact on firearm robbery.

How does research quality impact forensic experts? Forensic experts are expert witnesses who testify or provide forensic-related opinions in a court proceeding by virtue of their specialized knowledge.  The primary objective of a forensic expert is to educate judges and jurors on a particular topic in which the expert holds specialized knowledge beyond that held by the average person. In premises security litigation, security experts have specialized knowledge that is beyond that of an average juror and may be retained by one or both sides of a legal dispute to educate jurors. These experts provide a needed service, but opinions should be supported with high quality evidence. It is important to note here that many elements of security have not been subjected to research; however, the knowledge base is growing rapidly. Meta-Analysis and Systematic Reviews exist for Situational Crime Prevention, security lighting, video surveillance, and Crime Prevention Through Environmental Design (CPTED). Many Randomized Control Trials exist for law enforcement such as the Philadelphia Foot Patrol Experiment, but so few are directly applicable to the security industry. This leaves forensic experts to rely solely on other forms of evidence (e.g. industry best practices, guidelines) or anecdotal evidence. While an expert may rely on his/her training, education, and experience, the security industry needs to continue developing quality evidence.