title: Predicting general criminal recidivism in mentally disordered offenders using a random forest approach.
abstract: BACKGROUND
  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.
  
  
  METHODS
  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.
  
  
  RESULTS
  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).
  
  
  CONCLUSIONS
  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.
authors.affiliation: Department of Forensic Psychiatry, University Psychiatric Clinics, Wilhelm Klein-Str. 27, CH-4012, Basel, Switzerland. marlon.pflueger@upkbs.ch.
authors.forename: Marlon O
authors.initials: MO
authors.lastname: Pflueger
authors.affiliation: Department of Forensic Psychiatry, University Psychiatric Clinics, Wilhelm Klein-Str. 27, CH-4012, Basel, Switzerland. irina.franke@upkbs.ch.
authors.forename: Irina
authors.initials: I
authors.lastname: Franke
authors.affiliation: Department of Forensic Psychiatry, University Psychiatric Clinics, Wilhelm Klein-Str. 27, CH-4012, Basel, Switzerland. marc.graf@upkbs.ch.
authors.forename: Marc
authors.initials: M
authors.lastname: Graf
authors.affiliation: Department of Forensic Psychiatry, University Psychiatric Clinics, Wilhelm Klein-Str. 27, CH-4012, Basel, Switzerland. henning.hachtel@upkbs.ch.
authors.forename: Henning
authors.initials: H
authors.lastname: Hachtel
mesh_terms: D000328:Adult; D019540:Area Under Curve; D003415:Crime / Q000523:psychology / Q000706:statistics & numerical data*; D057237:Criminals / Q000523:psychology / Q000706:statistics & numerical data; D005260:Female; D005555:Forensic Psychiatry / Q000379:methods; D006801:Humans; D008297:Male; D001523:Mental Disorders / Q000523:psychology*; D012008:Recurrence; D018570:Risk Assessment; D012307:Risk Factors; D019966:Substance-Related Disorders / Q000523:psychology; D013557:Switzerland