Mental Illness and Violence: Proof or Stereotype?

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Acknowledgements

The researchers gratefully acknowledge the contribution of members of the Advisory Committee to this project:

Ms. Bonnie Pape,
Director of Programs,
Canadian Mental Health Association,
National Office,
Toronto, Ontario.

Ms. Susan Hardie,
Former National Coordinator,
National Network for Mental Health,
Guelph, Ontario.

Mr. Jim Holman,
Board Member,
National Network for Mental Health,
Guelph, Ontario.

Ms. Ann Braden,
President,
Schizophrenia Society of Canada,
National Office,
Don Mills, Ontario.

Mr. Alexander Saunders,
Chief Executive Officer,
Canadian Psychiatric Association,
Ottawa, Ontario.

Mr. James MacLatchie,
Executive Director,
John Howard Society of Canada,
Ottawa, Ontario.

Ms. Carol Silcoff,
Research Consultant,
Mental Health Unit,
Health Care and Issues Division,
Systems for Health Directorate,
Health Promotion and Programs Branch,
Health Canada.

Ms. Stephanie Wilson,
Program Officer,
Mental Health Unit,
Health Care and Issues Division,
Systems for Health Directorate,
Health Promotion and Programs Branch,
Health Canada.

The advice provided by Mr. Bob Shearer and Ms. Nena Nera of the AIDS Care, Treatment and Support Unit of Health Canada is gratefully acknowledged. The assistance of Marnie M. Hamilton, BSc., Research Assistant, who provided technical and library support is also acknowledged.

Preface

The issue of a possible relationship between mental illness and violence is not new. However, it is being increasingly highlighted through, for example, the work of the Federal/Provincial/ Territorial Implementation Work Group on the High-Risk Violent Offender Task Force Recommendations. This issue has also received attention in the non-governmental sector. Mental health advocates have traditionally stated that persons with mental illnesses are no more likely to commit violent acts than are persons who are not mentally ill. However, recent research and sensationalization of reports in the media have suggested that this may not be true, and that a certain subgroup of the mentally ill may be more violent than persons who are not mentally ill.

To help shed light on this complex and controversial issue, a critical review of the literature was commissioned by the Health Promotion and Programs Branch of Health Canada. A report was prepared under contract by Dr. Julio Arboleda-Flórez, Dr. Heather Holley, and Ms. Annette Crisanti, of the Calgary World Health Organization Collaborating Centre for Research and Training in Mental Health. Funding for this project was provided by the AIDS Care, Treatment and Support Unit under the National AIDS Strategy of Health Canada.

This project was a collaborative effort, with representatives from the Canadian Mental Health Association, the Schizophrenia Society of Canada, the Canadian Psychiatric Association, the National Network for Mental Health, and the John Howard Society of Canada sitting on an advisory committee.

The report is organized into five chapters. Chapter 1 provides an introduction to the report, and includes definitions, and a description of search strategies. 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. Key statistical associations reported in the literature are described. Chapter 3 critically reviews the evidence relating mental illness to violence with the aim of determining whether the statistical associations reported in the literature meet the epidemiological criteria for causality. A listing of the references used in Chapter 3 is included. Two Appendices are also included: Appendix A contains an annotated bibliography of articles reviewed. Appendix B contains a brief glossary of key technical terms.

This report should be of value to any of the myriad of Canadian players who are involved in the mental health, social services, and criminal justice sectors, including service providers, policy-makers, programmers, researchers, consumers or family members.

A note on language:

Terminology used to refer to serious mental health problems and to persons with serious mental health problems in the report, such as “psychiatric patient”, reflect the terms used by the authors of the articles reviewed. For the sake of accuracy, the terms have not been altered, although it is recognized that more commonly used terms such as “consumers” or “survivors”, may be preferred by some readers.

Executive Summary

Introduction and Rationale:

Mental health advocates have traditionally stated that persons with mental illnesses are no more likely to commit violent acts than are persons who are not mentally ill. However, there has been growing uncertainty as to the exact nature of the relationship, among caregivers, health care providers, and advocacy groups, spawned, on the one hand, by sensational media accounts and television dramas, and on the other, by conflicting scientific reports. This complex issue has important consequences for persons with mental disorders and their families, health care and social service providers, policy makers, programmers, and persons in the criminal justice system. To help shed light on this issue, this critical review of the literature was undertaken.

Search Strategy:

Computerized databases covering the scientific literature in the areas of psychology, sociology, criminology, law, medicine, philosophy, psychiatry, forensic psychiatry, and epidemiology were searched for any articles dealing with mental illness and violence. In order to maintain a broad search strategy, a number of different synonyms were used for the terms ‘mental illness' and ‘violence' resulting in 32 different search combinations and capturing over 5,500 unique citations. These reflected some 8,000 authors, 8,600 key words, 940 journals, and spanned some 30 publication years.

The review focused on articles published in the last 10-15 years because these were considered to represent the bulk of studies pertinent to present day populations of the mentally ill. 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 serious functional mental illnesses (such as schizophrenia or major depressive illnesses), substance abuse disorders (particularly alcohol abuse), and personality disorders (particularly antisocial personality disorder). To keep the review manageable, the definition of violence was restricted to acts involving physical assaults or threats to others, including violent criminal acts.

The report contains detailed abstracts of over 100 different articles pertaining to the relationship between mental illness and violence. Empirical studies are grouped according to a number of different topic areas, depending on main population of interest. These include (a) General Population Samples (b) Psychiatric Patients (c) Incarcerated Offenders (d) Other Empirical Studies of Interest, and (e) Reviews and Position Papers.

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 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 epidemiologic framework was used to make a judgement of causality. Epidemiology is concerned with the study of the occurrence of disease and health events in human populations and attempts to identify the factors that cause or influence these patterns. In the United States, courts of law have determined that statements of causality in human populations come most authoritatively from studies employing epidemiological criteria.

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.

Summary of Key Findings:

Studies cited in this review are drawn primarily from Canadian and American sources. A caveat must be noted with respect to generalizability of findings from the United States, where much of the research has been conducted, to Canadian populations. Interpretation and application of findings to the Canadian context must be cautiously undertaken in view of differences in the health care and criminal justice systems of the two countries.

A number of statistical relationships were reported throughout the literature. These are summarized as follows:

• The strongest predictor of violence and criminality is past history of violence and criminality. This was true regardless of diagnostic group (e.g., whether schizophrenia or substance abuse).
• As yet, there is no consistent evidence to support the hypothesis that mental illness (e.g., depression) that is uncomplicated by substance abuse is a significant risk factor for violence or criminality, once past history of violence is controlled.
• Whether persons with schizophrenia are at risk of violence depends, in part, on the context and the presence of psychotic symptoms. For example, persons with schizophrenia have been found to be at somewhat increased risk of committing violent acts when in the community, especially when they are experiencing psychotic symptoms. Conversely, violent behaviour has been found to be low among hospitalized patients with schizophrenia who are receiving appropriate neuroleptic medication.
• The occurrence of violent incidents among persons hospitalized with a mental illness may be increasing. However, a small number of these persons, typically those with acute psychotic symptoms or dementia, or who have a history of prior violence, have usually been found to be responsible for the majority of violent incidents. Most violent incidents leading to hospitalization occur in the home, and involve episodes of damage to furniture or minor assaults to relatives.
• Formerly hospitalized mental patients may be at high risk of arrest and violence when released into  the community, particularly if they have a history of prior arrests or violence or if they experience psychotic symptoms;
• Family members (not the general public) are the most likely targets of violence from formerly hospitalized patients in the community;
• Substance abuse appears to be a significant risk factor for violence and criminality among community, hospitalized, and offender populations. It is unlikely that a member of the public would be at risk of violence from someone with a non-substance abuse disorder;
• Studies of police-citizen encounters in both Canada and the United States show that the pattern of criminality among persons with mental illness and persons without mental illness coming into contact with the police is similar. Persons with mental illnesses are no more likely to be charged with a violent crime compared to those persons who do not have a mental illness;
• The prevalence of substance abuse disorders and mental disorders is high among remanded and provincially incarcerated offenders. Yet, the overall rate of detection of mental illness by correctional staff appears to be quite low. Explanations for the high prevalence of mental illness among incarcerated offenders have included the “criminalization” of mentally disordered behaviour, the “psychiatrization” of criminal behaviour, and the pathogenic nature of incarcerated environments;
• In general, offenders' post-release adjustment does not appear to be related to major mental illnesses (such as schizophrenia or depression) or substance abuse disorders when prior criminality and age are controlled; and
• Most generally, individuals who are younger are at higher risk of violence and criminality.

Does Mental Illness Cause Violence?

A critical analysis of the literature reveals that as yet, there is no compelling scientific evidence to suggest that mental illness causes violence.

Studies of violence among the treated mentally ill population demonstrate that this population does have higher levels of criminality and violent criminality compared to the general population, and a high incidence of violence while in hospital. Similarly, studies of mental illness among incarcerated offenders have shown a high prevalence of serious mental disorders and substance abuse disorders. However, despite such clear demonstrations, these findings do not support the conclusion that mental illness causes violence for the following methodological reasons:

• It is not always clear how comparisons across study groups should be adjusted to take account of factors such as age, sex, socio-economic status, prior arrests, or prior institutionalizations. For example, many authors have used violent criminality as a measure of violence. However, it is known that the relationship between mental illness and violent criminality depends on whether  study groups are statistically comparable with respect to other characteristics that predict crime such as socio-economic status, age, or prior arrest histories. When study groups are comparable on these factors, the relationship between mental illness and violence often disappears. However, authors have dealt with these issues differently, depending on their understanding of the causal process underlying the relationship between mental illness and violence and as yet, no study has appropriately dealt with all of these factors. Therefore, it is difficult to draw firm causal conclusions.
• Using current psychiatric diagnostic conventions, it is not possible to diagnose mental illness independently from violence. Almost half of the disorders described in the North American standard Diagnostic and Statistical Manual for Mental Disorders, Third Edition, Revised (DSM-III-R) (American Psychiatric Association, 1987) are described or defined in part on the basis of violent behaviours and similar criteria are used in the more recent DSM-IV (American Psychiatric Association, 1994). These include schizophrenia, bipolar disorder, substance abuse, and some personality disorders. Over time, our concept of mental disorder has changed to incorporate more criteria pertaining to violence. Therefore, it is likely that the more recent studies that show a statistical relationship between mental disorder and violence are an artifact of the way we have come to define and measure these conditions.
• A number of commonly used psychiatric medications (including tranquilizers/ sedatives) have been reported to cause aggression. It is not known to what extent such paradoxical reactions could account for violence among the mentally ill receiving short and long-term psychopharmacological treatments.
• Virtually all studies conducted to date have based their results on treated populations of persons with mental illness or incarcerated offenders. These groups are not representative of all persons with mental illnesses. These studies are biased toward those sub-populations of persons with mental illness who are more prone to violence. Current civil committal legislation, which is based on a standard of dangerousness, ensures that persons who are dangerous to themselves or to others are admitted to hospital. If persons do not meet the more stringent committal criteria and refuse hospitalization, they may be arrested in order to access mental health services through correctional routes. Because of these selection pressures, results based on treated populations will lead to exaggerated estimates of the relationship between mental illness and violence.
• Many studies have relied on institutional records (such as admissions to a psychiatric facility or arrests) to classify their subjects. Clearly, institutional records do not correctly classify all persons with a mental illness or all persons who have committed a violent act. Too often, official statistics reflect political biases and  social trends and this interferes with the appropriate interpretation of the data.
• Primary data collected from general population samples have the greatest potential to produce valid results bearing on the issue of mental illness and violence. To date, however, only two studies in the general population have been conducted—one in the United States and one in (Alberta) Canada. Both used state-of-the-art epidemiological survey techniques and representative samples of the general population. Both studies used a structured diagnostic interview schedule for DSM-III-R diagnoses to define mental disorders. Items referring to violent behaviour used to derive these psychiatric classifications were then used to define violence. While both studies report a statistical relationship, it is not clear whether this could be explained by the lack of independence in the way mental illness and violence were defined. Secondly, neither study was able to establish temporal ordering of factors; a crucial omission. Therefore, it is not clear whether the violence preceded the mental illness, or vice versa. Only when mental illness precedes violence can a causal interpretation be made.
  

Potential Directions for Future Research:

We are not yet at the stage where it is possible to make a valid causal judgement about the relationship between mental illness and violence. Yet, based on our current knowledge from biochemical and genetic studies, a link between these two remains biologically plausible.

Several methodological challenges lay ahead for future research. Perhaps most importantly, we must develop independent measures of mental illness and violence. The DSM standard psychiatric nosology has limited application in this area given that almost half of the disorders are described or defined in part on the basis of violent acts. Secondly, researchers must move out of institutions to measure the relationship of mental illness and violence in unselected or representative samples. Finally, longitudinal follow-up designs which permit clear temporal ordering of factors and appropriate treatments for factors such as age, sex, socio-economic status, and prior violence must become the gold standard. Until such studies are completed, there can be no scientific basis for concluding that mental illness causes violence.

The paucity of published literature incorporating the perspective of those who have a mental illness should also be addressed. The views and experiences of consumers and their family members would contribute further to the examination of violence as it is experienced by these individuals in community and hospital settings, and among peers. This is an area where future work is needed.

While not the subject of the current review, the research reviewed in this study raises questions in regard to the extent to which the following issues are being addressed:

• Appropriate identification of mental illness and substance abuse problems among incarcerated offenders in correctional settings.
• Management of disturbed behaviour by the mentally ill that is often directed towards family members. Such approaches are being used in hospital settings.
• Appropriate access to community resources for former mental patients in the community.
• Appropriateness of treatment for the mentally ill in correctional and community settings.

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