Violence by Psychiatric Patients: The Impact of Archival Measurement Source on Violence Base Rates and Risk Assessment Accuracy

Objective: This study examined the impact of using various archival sources of violence data on the recorded base rate of violence and on the accuracy of violence risk assessments in a sample of civil psychiatric patients. Method: Violence in the community, after release from involuntary hospitalization, was measured with 3 types of archival data: criminal records, psychiatric hospital readmission records, and readmission records from multiple general hospitals. Results: Findings indicated that the different measurement sources each identified unique incidents of violence, which were correlated moderately or not at all with one another, and that the estimated base rate of violence varied substantially as a function of outcome source. Not surprisingly, using a combination of sources identified the highest base rate of violence. Predictive validity estimates also varied widely under different measurement procedures and were more stable when a combination of sources was used. Conclusions: It is important in practical and research terms for studies of psychiatric patient violence to use multiple sources of outcome data. (Can J Psychiatry 2003;48:734-741)