External Validity of Studies on Aggressive Behavior in Patients with Schizophrenia: Systematic Review

Tilman Steinert1, *, Karen Hamann2
1 Centre for Psychiatry Suedwuerttemberg, Ulm University, Germany
2 Rhein-Jura Klinik, Bad Saeckingen, Germany

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© Steinert and Hamann; Licensee Bentham Open.

open-access license: This is an open access article licensed under the terms of the Creative Commons Attribution Non-Commercial License ( which permits unrestricted, non-commercial use, distribution and reproduction in any medium, provided the work is properly cited.

* Address correspondence to this author at the Centre for Psychiatry Suedwuerttemberg, Ulm University, Weingartshofer Straße 2, 88214 Ravensburg Weissenau, Germany; Tel: (+49) 751-7601-2738; Fax: (+49) 751-7601-2767; E-mail:


Studies on violence in schizophrenia use two different approaches: use of epidemiological data, and clinical studies recording direct patient data after gaining informed consent. With regard to informed consent requiring agreement and cooperation, the question arises as to what extent participants represent patients with schizophrenia and violent behaviour (external validity). We conducted a systematic literature research. In most of the studies, aggression or violence, respectively, were poorly defined. Only 5 (15.2%) studies used a cut-off score on an aggression scale. Only 6 studies (18.2%) reported the number of patients who refused to participate, and 16 (48.5%) reported the number of drop-outs. Only 3 studies (9.1%) reported a systematic comparison of participants and non-participants. We found that data which allow for the assessment of representativeness of the investigated samples are poorly reported. For most studies, doubts regarding external validity seem justified and generalisability is questionable due to possible selection bias.

Keywords:: Aggression, external validity, review, schizophrenia, violence.