Probleme der Prognose von Gewalt durch psychisch Kranke

Abstract

In many societies legislators try to reduce the number of criminal acts, especially acts of violence, by laws requiring the assessment and prediction of dangerousness of individuals known for criminal violence. The paper discusses the problems of predicting criminal violence by mentally ill subjects. After elaborating the intricate theoretical and methodological difficulties facing any variant of prediction of behavior the author explains why it is so difficult to compare the predictive power of several prediction instruments. Such a comparison is essential for any attempt to determine the most powerful instrument for special groups of subjects. In the second part the paper documents and discusses the power of several new instruments (VRAG, HCR-20, PCL-R for instance) predicting violence of mentally ill patients. Though when using these prediction instruments the results in most cases are superior to mere chance models they leave a lot of serious questions open because even the better instruments are confronted with the problem to combine a moderate sensitivity with an intolerable rate of false positives or a high rate of negative prediction with an intolerable low positive prediction rate.