Quantifying violence in mental health research

• Violence and mental illness research is limited by variation in defining violence.
• Multiple sources and assessments provide richer information about violence.
• Detailed information is often diluted as a result of dichotomization of groups.
• This presents methodological challenges for the field.
• Future studies should move from defining, towards quantification of violence.

Research into mental illness and its relationship with violence has been constrained by inconsistencies in the definition and measurement of violent behavior. We conducted a systematic literature search of Scopus, EMBASE, PsycINFO, and Ovid Medline with search terms relating to the measurement, rating and quantification of violent behavior in mentally disordered populations. We identified nine tools designed to assess violence and critically evaluated them. Broadly, measurement tools tended to focus on multiple, but different, facets of violence, which included: severity of act, severity of outcome, frequency and intent, with each suggested as a valid outcome measure for violent acts. The use of multiple sources of information to inform assessment appears to provide detail; however, that detail is then often diluted as a result of dichotomization of sample groups. This presents methodological challenges for the field. Future studies should give consideration to the trade-off between preserving the richness of data and the difficulties associated with recruiting large patient samples. Studies should move from simply defining violence towards quantification across different dimensions of violence and using multiple sources of information.