Predicting general criminal recidivism in mentally disordered offenders using a random forest approach

• Published in: BMC psychiatry Vol. 15; no. 1; p. 62
• Main Authors: Pflueger, Marlon O, Franke, Irina, Graf, Marc, Hachtel, Henning
• Format: Journal Article
• Language: English
• Published: England BioMed Central Ltd 29.03.2015; BioMed Central
• Subjects: Adult; Area Under Curve; Behavior; Crime - psychology; Crime - statistics & numerical data; Criminals - psychology; Criminals - statistics & numerical data; Female; Forensic Psychiatry - methods; Health aspects; Humans; Male; Mental Disorders - psychology; Mentally ill; Recidivism; Recurrence; Risk Assessment; Risk Factors; Substance-Related Disorders - psychology; Switzerland; Switzerland
• ISSN: 1471-244X; 1471-244X
• DOI: 10.1186/s12888-015-0447-4

Psychiatric expert opinions are supposed to assess the accused individual's risk of reoffending based on a valid scientific foundation. In contrast to specific recidivism, general recidivism has only been poorly considered in Continental Europe; we therefore aimed to develop a valid instrument for assessing the risk of general criminal recidivism of mentally ill offenders. Data of 259 mentally ill offenders with a median time at risk of 107 months were analyzed and combined with the individuals' criminal records. We derived risk factors for general criminal recidivism and classified re-offences by using a random forest approach. In our sample of mentally ill offenders, 51% were reconvicted. The most important predictive factors for general criminal recidivism were: number of prior convictions, age, type of index offence, diversity of criminal history, and substance abuse. With our statistical approach we were able to correctly identify 58-95% of all reoffenders and 65-97% of all committed offences (AUC = .90). Our study presents a new statistical approach to forensic-psychiatric risk-assessment, allowing experts to evaluate general risk of reoffending in mentally disordered individuals, with a special focus on high-risk groups. This approach might serve not only for expert opinions in court, but also for risk management strategies and therapeutic interventions.