METHODS

This review involved conventional systematic searching, data extraction, and synthesis methods. Specifically, a comprehensive search of the literature was undertaken using electronic databases (Academic Search Complete, PubMed, PsycINFO, EMBASE, Web of Science, Sociological Abstracts, Social Science Abstracts, PAIS International and Lexis-Nexis), the Internet (Google, Google Scholar), and article reference lists. Search terms included violence, homicide, prohibition, drug law enforcement, enforcement, drug crime, gangs, drug gangs, and gun violence. The terms were searched as keywords and mapped to database-specific subject headings or controlled vocabulary terms when available. Each database was searched for English language articles from its inception to its most recent update as of October 2009.

Inclusion & Exclusion Criteria

Studies published in peer-reviewed journals, ab stracts from international conferences, and publications from governments and nongovernmental organizations that reported on a link between drug law enforcement, illicit drug strategies, and violence were all eligible for inclusion in the systematic review. Editorials, advocacy articles, and studies of police violence were excluded. We also excluded studies that focused on violence associated with military action against insurgencies funded through the drug trade.

Data Collection Process

Two investigators (DW, GR) conducted data extraction independently, in duplicate, using standardized techniques. Data abstractors collected information about the study design, sample size, methods of effectiveness measurement, and outcomes (i.e., violence). The data were entered into an electronic database such that duplicate entries existed for each study; when the two entries did not match, consensus was reached through discussion.

Data Items & Summary measures

The primary outcome of interest for this review was to identify reported associations between drug law enforcement and violence. Given the heterogeneity of the literature on drug law enforcement, in some instances proxy measures were used for both drug law enforcement (e.g., numbers of drug arrests, police officers) and violence (e.g., numbers of homicides, shootings).

Data Synthesis
To ensure scientific rigour, the Preferred Reporting of Systematic Reviews and Meta-Analyses (PRISMA) guidelines were used for systematic data synthesis .22 These guidelines are widely recognized as the gold standard in trans parent reporting of systematic evaluations of scientific research questions.

Because studies included in this systematic review varied extensively regarding methodologies and outcomes, findings were summarized on a per-study basis, and statistical data were entered into a standardized form. When reporting results from individual studies, the measures of association and p values reported in the studies were cited.