Mental Illness and Violence: Proof or Stereotype?

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1 Introduction

Study Mandate:

Objective and systematic study of the relationship between mental illness and dangerousness is crucial to the formulation of appropriate and effective policies for the provision of mental health services (Davis, 1991). This is true regardless of whether the service is required in the community, within the mental health system, or within correctional settings. Evidence supporting a relationship between mental illness and violence is also pivotal in the debate concerning the appropriate use of involuntary hospitalization, the design of community-based controls for violence among persons with mental illness (Mulvey, 1994), and the utilitarian need to understand the social consequences of deinstitutionalization policies (Mulvey, Blumstein, and Cohen, 1986).

In the post-deinstitutionalization era, negative community attitudes and fears, fostered in part by selective media reporting, have surfaced as the most persistent obstacle to the fulfilment of community-based treatment goals (Rabkin, 1979; Steadman, 1981). In addition, current health restructuring, which is occurring in all parts of Canada, will place unprecedented pressure on general hospital psychiatric programs and psychiatric facilities to transfer persons with mental illness to the community and to drastically curtail subsequent lengths of stay and even access for acute treatment.

While the claim that the mentally ill are violent has been traditionally opposed by mental health advocates and researchers (e.g. Monahan and Steadman, 1983), recent literature reviews written by prominent researchers in the field (e.g. Monahan 1993; Torrey, 1994) now suggest that mental illness may be causally connected to violence, particularly for certain sub-groups of the mentally ill. Faced with a second major wave of dehospitalization, and renewed scientific controversy, it is an opportune time to re-ask the question: is there compelling scientific evidence to support a causal understanding of the relationship between mental illness and violence?

The following critical appraisal of the literature was commissioned by the Health Promotion and Programs Branch of Health Canada. An advisory committee guided this project and was composed of representatives from the Mental Health Unit of Health Canada, the Canadian Mental Health Association, the Canadian Psychiatric Association, the John Howard Society of Canada, the National Network for Mental Health, and the Schizophrenia Society of Canada. The critical appraisal of the literature was conducted by psychiatric epidemiologists from the Calgary World Health Organization Centre for Research and Training in Mental Health in Alberta, Canada. This work complements a meta-analytic study focused on predictors of recidivism among the mentally disordered offender population underway at the Solicitor General of Canada. Findings should be available within the coming months.

Target Audience for this Report:

While the issues addressed by this report are of interest to mental health providers, persons with mental illness, and their families, and while every effort has been made to avoid unnecessary jargon, this report may be more readable by persons with some familiarity with scientific concepts. A glossary of terms (Appendix B) has been included to assist non-technical readers in understanding the use of key terms and a non-technical companion report is currently under development.

Definition of Terms:

Serious Mental Illness:

In order to make the results of this investigation useful to the widest possible audience, studies dealing with a variety of mental disorders were assessed including conditions such as schizophrenia, major depressive illnesses, substance abuse disorders, and personality disorders. The bulk of the literature reviewed relied on Diagnostic and Statistical Manual of Mental Disorders, Third Edition, Revised (DSM-III-R) as the standard diagnostic nosology (American Psychiatric Association, 1987). However, studies were not excluded from review if they used earlier versions of this nosology or another nosology.

A number of key words were used when conducting the computerized search to capture articles studying violence among the seriously mentally ill. These included:

• Mental disorder
• Mental illness
• Mentally ill offenders
• Psychiatric patients

Violence:

The term ‘violence' was used quite loosely throughout the literature to refer to a wide range of behaviours including acts involving physical assault, physical threats, verbal threats, psychological or emotional abuse, damage to property, suicide, and self-harm. This review focuses on violence toward others, as opposed to violence expressed toward the self. Violence toward others was broadly conceptualized to reflect behaviours of persons against others that were meant to intentionally threaten or actually inflict physical harm. Many researchers measured violence with reference to criminal acts involving arrests or convictions for violent crime.

We considered a definition that restricted ‘violence' to interpersonal physical acts to be appropriate for a number of reasons. First, if there is a causal relationship between mental illness and violence, it should be most easily detected in its most extreme manifestations. Second, the occurrence of physical violence can be determined more reliably, therefore, is likely to be more consistently defined and reported from study to study.

Synonyms for violence used in conducting the search strategy included:

• Violence
• Aggression
• Dangerous
• Violent behaviour
• Assault
• Crime
• Criminality
• Battery

Search Strategy:

Peer-reviewed articles published over the last 10-15 years were the main target for review because these represent the bulk of studies pertinent to present day populations of persons with mental illness. Exceptions to this rule were made for particularly interesting, informative, or “classic” studies. Similarly, while our main emphasis was on reviewing quantitative empirical studies, key qualitative studies and literature reviews were also included.

The search for appropriate material began with a structured investigation of four computerized databases (PsychLit, Index Medicus, Sociofile, and the Calgary WHO Collaborating Centre Forensic Holdings) representing peer-reviewed literature from psychology, sociology, law, criminology, medicine, philosophy, psychiatry, forensic psychiatry, and epidemiology. The critical analysis was restricted to peer-reviewed journals as these are known to meet minimum standards for scientific validity. Articles were reviewed in English, French, and Spanish. Non-English articles that were considered appropriate for inclusion in the annotated bibliography have been annotated in English. Also, because computerized bibliographic systems have been shown to miss many pertinent articles (e.g. Adams, Power, Frederick, and Lefebvre, 1994), relevant publications were also sought from the reference lists of articles that were reviewed.

The various key words for mental illness and violence (described above) resulted in a maximum of 32 different search combinations per database. As the search progressed and we became familiar with the most productive key words, it was possible to progressively narrow the search strategy. For example, it became clear after the first search that the term “battery” was used largely to refer to psychological test batteries. This term was dropped from subsequent searches. Some databases (such as Index Medicus) used fewer synonyms for mental illness and criminality so this reduced the number of search combinations.

Over 5,500 unique citations were captured from the computerized searches using the keyword combinations. These reflected some 8,000 authors, 8,600 key words, 940 journals, and spanned some 30 publication years. In order to manage this volume of material, complete references and all available abstract data were electronically downloaded to a desk-top computer-based system equipped with specialized software for further processing. This software proved  indispensable in identifying and eliminating duplicate references that appeared in more than one library database, and for creating lists.

A listing of citations and complete study abstracts was produced for the first level of critical review. So as not to overlook relevant citations, this list was reviewed independently by two members of the research team. Copies of articles were then retrieved from the library for more detailed critical review. Local library holdings provided access to the major North American and European journals. Inter-library loans provided access to the less accessible publications.

Of the original 5,500 citations, some 400 articles were retrieved from the library and reviewed in detail using standard epidemiological criteria. Those included in the annotated bibliography are based on our best judgement that they constitute the key publications in the area.

Critical Review Strategy:

Because of the stigma that could result from a premature and unproven statement purporting a causal relationship between mental illness and violence, this review has adopted a rigorous and conservative scientific perspective that permits a judgement of causality only (a) in light of compelling confirmatory evidence from well-designed and executed studies, and (b) given that no compelling disconfirmatory evidence exists.

An epidemiological framework was used to make a judgement of causality. Epidemiology is concerned with the occurrence of disease and health events in human populations and attempts to identify the factors that cause or influence these patterns (Lilienfeld and Stolley, 1994). In the United States, courts of law have determined that statements of causality in human populations come most authoritatively from studies employing epidemiological criteria (e.g. Brock v. Merrell Dow Pharmaceuticals, 1989; Daubert v. Merrell Dow Pharmaceuticals, Inc., 1993).

Epidemiologists adhere to a hierarchy of evidence placing the most credence in statistical associations demonstrated in well-designed and executed cohort studies. These studies define subjects on the basis of the presence or absence of mental illness and follow two or more groups through time to compare outcomes. Case-control study designs that define subjects on the basis of outcome (e.g. presence or absence of violence) then collect retrospective data on the presence or absence of mental illness, can provide persuasive evidence but are usually not deemed to be sufficiently strong to make a causal judgement. Descriptive cross-sectional surveys are used to generate hypotheses for further testing. Because data on both mental illness and violence are collected simultaneously, it is difficult to ensure that the mental illness predated the violence, as would be required for a causal relationship. Therefore, results from surveys are not used to infer causality.

Organization of this Report:

This report is organized into three main sections. Chapter  2 summarizes the main findings from the literature according to three broad themes: community-based studies, studies of the mentally ill population, and studies of incarcerated offenders. The aim of this chapter is to describe the key statistical associations that have been reported in the literature. Statistical associations that are strong and appear consistently across different types of studies conducted in different locations are considered to be most noteworthy. Chapter 3 critically reviews the evidence relating mental illness to violence with the aim of understanding whether the statistical associations reported in the literature meet the epidemiological criteria for causality. A listing of the references used in Chapter 3 is also included. Appendix A presents the annotated bibliography of articles used in this report. These are organized according to themes: main population of interest (community studies, studies of psychiatric patients, and studies of incarcerated offender populations), other empirical studies of interest, and review articles. Within each broad theme, articles are organized alphabetically, according to author and title. To assist the non-scientific reader in drawing pertinent comparisons across articles, all empirical studies have been critically reviewed and summarized according to a standardized abstract structure: (a) purpose and objective, (b) research design, (c) study setting, (d) study subjects, (e) measures used, (f) main findings, (g) conclusions, (h) methodological critique, and (i) causality. Appendix B contains a brief glossary of key technical terms.

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