I recommend the Primary Papers

The recent study by Fazel et al. (2009) is based on a sample comprising what amounts to be the entire population of schizophrenia patients in Sweden. This is a major strength of the study. The principal outcome of interest was conviction for violent crime. The authors reported odds ratios for violent crime in patients with and without substance abuse comorbidity, compared to a control group.

Schizophrenia patients commit acts of violence in the community and in the hospital. In the United States, arrests of psychiatric inpatients for assaults and other aggressive behaviors that they commit are rare, and prosecution leading to conviction is extremely unlikely. I suspect that the situation in Sweden is not dramatically different in this respect. If this is so, I have some comments.

First, schizophrenia patients generally spend more time in hospitals than members of the general population do. A minimum of two hospitalizations was an eligibility criterion for inclusion in the group of schizophrenia patients in this study. During hospitalization, they were not available to be arrested and convicted. Given these facts, it is likely that the patients had, on average, less time to commit convictable violent crime than members of the comparison group. It appears that the authors did not account for this difference in time exposure in their analyses. If so, the odds ratios they computed were underestimates.

Second, we need to keep in mind that violence by schizophrenia patients in the hospital is common (Volavka, 2002). This is not surprising, since violence is a leading cause prompting hospitalization, and patients are not discharged until the risk for violence is deemed acceptably low. Therefore, if violent patients were not hospitalized, violent behavior by schizophrenia patients in the community would occur at a substantially higher rate. Thus, the odds ratio for conviction for violent crime is kept low by the constant removal from the community to hospitals of the patients who are the most violent at the moment. Furthermore, if violent acts of hospitalized patients, such as causing injuries to others (which would be considered criminal if the patient were in the community), were included in the Fazel et al. analyses, the odds ratio would increase.

References:

Fazel S, Långström N, Hjern A, Grann M, Lichtenstein P. Schizophrenia, substance abuse, and violent crime. JAMA. 2009, May 20; 301(19):2016-2023. Abstract

Volavka J. Neurobiology of Violence. 2002. Washington, DC: American Psychiatric Publishing, Inc.

View all comments by Jan Volavka

  I recommend the Primary Papers

Comment by Seena Fazel, Martin Grann, and Niklas Långström
We are grateful for the interest and comments that our paper has attracted. We would like to take this opportunity to respond to some of these comments.

First, Dr. Volavka raises the potentially important issue of time at risk and whether the patients had less time at risk than the controls. In Sweden, any serious offences by hospital inpatients are reported to the police and lead to convictions. This is partly a consequence of the insurance system, which requires police involvement if insurance claims are made by health care workers or other patients. It is possible that minor offending, such as theft, by hospital patients does not lead to conviction, but our study focused on violent offending.

Second, we agree with Dr. Torrey that our comments about treatment for substance abuse comorbidity in patients should not detract from the need for treatment of the underlying schizophrenia. A recent review reinforces Dr. Torrey’s point and suggests that consideration should be given to using second-generation antipsychotics (Wobrock and Soyka, 2008).

Third, Dr. Hodgins states that our study “failed to provide information that could be relevant to improving treatments and services to reduce violence in this population.” However, it is possible to argue that our study does clearly endorse the case for good-quality randomized controlled trials for the treatment of comorbidity in schizophrenia, which have been lacking, according to a recent review (Wobrock and Soyka, 2008). In addition, our study underlines the importance of the assessment and management of comorbidity to reduce violence risk.

Fourth, Dr. Hodgins states that we were “inaccurate” to state that our study was larger than previous studies combined. In fact, we stated that it was larger than all longitudinal studies combined. A systematic review of all studies examining the risk of violence in schizophrenia that clearly demonstrates this is coming out in the August issue of PLoS Medicine (Fazel et al., 2009). Even if you assume (incorrectly) that we said that our study was larger than all previous studies combined, then the number of individuals with schizophrenia in the other 19 studies that we identified from 1980-2009 (longitudinal and other) included 10,420 patients. Our study included 8,003 patients with schizophrenia.

Fifth, Dr. Hodgins makes an interesting point about gender differences. This was not the focus of our paper, which examined primarily familial factors and substance abuse comorbidity over 30 years in patients with schizophrenia in Sweden. However, the review in PLoS Medicine finds an overall non-significant association toward higher risk estimates in female compared with male patients, which may not be quite as strong an effect as Dr. Hodgins suggests.

Finally, we agree with, and acknowledged in our paper as limitations, the comments about lack of information about treatment and a history of conduct disorder. However, including reliable and valid information on these and other more detailed potential risk factors in large population-based studies will remain an ongoing challenge to all research in the field.

References:

Wobrock T, Soyka M. Pharmacotherapy of schizophrenia with comorbid substance use disorder--reviewing the evidence and clinical recommendations. Prog Neuropsychopharmacol Biol Psychiatry. 2008 Aug 1; 32(6):1375-85. Abstract

Fazel S, Gulati G, Linsell L, Geddes JR, Grann M (2009) Schizophrenia and Violence: Systematic Review and Meta-Analysis, PLoS Med 6 (8). Abstract

View all comments by Seena Fazel