Mental Illness and Violence: An Epidemiological Appraisal of the Evidence
J Arboleda-Flórez MD, FRCPC, FAPA, DABFP, PhD1
Objective: To conduct a critical review of the literature on the matter
of mental illness and violence, to examine whether there is enough evidence
to establish a causal link, and to provide epidemiological background to
measure the risk to the population.
Method: Based on a computerized search of the literature on mental illness
and violence previously conducted for Health Canada, studies in the area
were critically reviewed and divided into 3 main categories: 1) studies
of criminal and violent behaviour among psychiatric patients, 2) studies
of psychiatric illness among offenders (prevalence studies in institutions,
analytical studies, and community follow-up of offenders), and 3) epidemiological
community-based studies on the issue of mental illness and violence (police–citizen
encounters, representative samples, and other epidemiological studies).
Causality rules and measures of risk were then applied to the evidence
Results: The review of the literature suggests that only a small minority
of hospitalized patients, typically those suffering from acute psychotic
symptoms, are involved in violent incidents. Formerly hospitalized patients
are at a higher risk of committing violence if they are not properly treated
and are experiencing threat/control-override psychotic symptoms. Substance
abuse disorders significantly raise the risk for violence. Family members
are the most at risk of being victimized.
Conclusion: An association exists between mental illness and violence,
but the many covariations that naturally affect the equation between them
introduce uncertainties in establishing causality.
(Can J Psychiatry 1998;43:989–996)
Key Words: deinstitutionalization, violence, criminalization, offenders, causality
Advocates for mentally ill persons have traditionally stated that persons
with mental illness are no more likely to commit violent acts than are
persons who are not mentally ill. This long-sustained position has become
harder to hold in light of sensational media coverage of crimes committed
by mentally ill persons (1), television dramas that depict mentally ill
persons as dangerous (2,3), and scientific reports that point toward an
association between mental illness and violence (4–6). That an association
exists seems to be an accepted fact, but the exact nature of the association
remains to be determined. This complex issue and its final resolution have
important consequences for persons who suffer from mental disorders and
their families, health care providers, legislators, programmers, and personnel
in the justice and criminal systems (7).
Objective and systematic study of the relationship between mental illness,
violence, and dangerousness is crucial to the formulation of appropriate
and effective policies for the provision of mental health services (8).
This proposition-like statement holds true regardless of whether the service
is required in the community, the mental health system, or correctional
settings. Evidence supporting a relationship between mental illness and
violence is also pivotal in the debate concerning the appropriate use of
involuntary hospitalization, in the design of community-based controls
for violence among persons with mental illness (9), and in the utilitarian
need to understand the social consequences of deinstitutionalization (10).
In the postdeinstitutionalization era, negative community attitudes and
fears have been cited as the most persistent obstacle to the fulfilment
of community-based treatment goals (11,12). In Canada, these attitudes
and fears may also obstruct health restructuring initiatives that are placing
unprecedented pressures on psychiatric facilities to transfer persons with
mental illness to the community, to curtail lengths of stay, and to reduce
access to psychiatric beds.
While the claim that mentally ill persons are violent traditionally has
been opposed by mental health advocates and researchers (13), recent literature
reviews and research reports suggest that mental illness may be causally
connected to violence, particularly for certain subgroups of the mentally
ill population (14,15). As we confront a major second wave of dehospitalization
and renewed scientific controversy, it is indeed very pertinent 1) to review
the literature on mental illness and violence, 2) to question whether compelling
scientific evidence already exists to support a causal understanding of
the relationship between them, and 3) to assess the potential risk that
mental patients could pose to the community.
This paper, therefore, presents a review of the literature on mental illness
and violence and undertakes a critical epidemiological appraisal of the
evidence in regard to causality and potential risk.
Studies that have examined the relationship between mental illness and
violence have focused on the violent behaviour of identified psychiatric
patients or on the presence of mental illness among identified offenders.
With some overlap, these studies could be divided into 3 large categories:
1) studies of psychiatric patients, 2) studies of offenders, and 3) epidemiological
Studies of Psychiatric Patients
About 20% of studies (7) on mental illness and violence have focused on
physical violence of hospitalized psychiatric patients. Most of these studies
have concluded that a small percentage of patients (about 5%) are responsible
for just over one-half of all violent incidents and for more than one-half
of the serious injuries (16,17). Patients with psychotic symptoms, particularly
paranoid symptoms, have been found to be at a higher risk for physical
aggression toward others (18–20), and among psychogeriatric patients, those
suffering from dementia have been shown to present a greater risk of violence
(21). Noble and Rodger report an increase of violent incidents occurring
in hospitals between 1976 and 1984 (18). Similarly, Volavka and others
report an increasing trend in the prevalence of arrests of psychiatric
patients for incidents that occurred while in hospital (22).
In a study in a university-based, locked, short-term psychiatric inpatient
unit, Straznickas and others found that 19% of patients (113 of 581) had
physically attacked someone in the 2 weeks prior to their admission (23).
Among those who had assaulted someone, 50 had assaulted people outside
of the family, 10 had assaulted both family members and individuals outside
of the family, and 53 had assaulted only family members. In addition, 31
of those patients who were assaultive had attacked more than 1 person.
Violence and fear-inducing behaviour have been found to be characteristic
of the acute exacerbations of chronic conditions such as schizophrenia
or mania leading to hospitalization. For example, Binder and others found
that 21% of randomly selected inpatients (N = 150) in a university psychiatric
unit had attacked persons and that 25% had engaged in fear-inducing behaviour
in the 2 weeks prior to their admission (24). This was especially true
for patients suffering from schizophrenia or mania. In addition, 13% of
patients attacked others during their admission, and 32% engaged in fear-inducing
behaviour. Patients with a diagnosis of mania were more likely to attack
others, while those with a diagnosis of schizophrenia were more likely
to engage in fear-inducing behaviour.
Many studies have examined the relationship of specific symptoms and diagnoses
to violence. Link and Stueve compared a sample of 232 patients, 42 of whom
were inpatients, with a community representative sample of 521 individuals
chosen from the same neighbourhood as the patients (25). Current and former
patients were significantly more likely to have engaged in hitting, fighting,
and weapon use than never-treated community controls, and this association
remained when groups of patients were divided into more detailed treatment
groups (first-contact, repeat-contact, former patients). Patients who were
suffering from threat/control-override psychotic symptoms were more likely
to engage in violent behaviours. This finding was associated with a strong
dose response, so those patients at the high end of the scale were more
prone to violent acts than those at the lower end. The authors concluded
that the threat/control-override symptom scale largely explained the association
between patient status and violence.
Perhaps the most consistent and striking findings are the association of
substance abuse disorders (alcohol and/or drug abuse) to violence and criminality
and the small association or lack of association of other disorders (for
example, schizophrenia, affective disorders, anxiety disorders) to violence
(26). The relationship of substance abuse disorders and violence was indicated
as early as 1974 (27). Guze and others demonstrated that patients with
diagnoses of sociopathic personality disorder and substance abuse were
more likely to have a history of felony convictions. This finding led the
authors to conclude that sociopathy, alcoholism, and drug dependence were
the principal psychiatric disorders associated with crime. Similar findings
have been reported in more recent studies (28,29).
The importance of substance abuse as a predictor of violence was found
to hold, even when studies were restricted to a single diagnostic group,
such as patients with schizophrenia. Cuffel and others, for example, studied
only patients who had been diagnosed with schizophrenia to determine whether
a comorbid substance abuse diagnosis increased the risk of subsequent violence
(30). Data were gathered from a retrospective review of files of 103 outpatients.
Violent behaviour was broadly defined from verbal threats to destruction
of property and physical assaults. Patients who were polysubstance abusers
were found to be significantly more likely to commit a violent act.
Another significant finding from this body of research points to the importance
of prior violence and criminality in predicting subsequent violence and
criminality (31–34). This relationship is important because of the high
percentage of mentally ill patients who report prior criminal and violent
acts (29,35). Cirincione and others, after controlling for the effects
of arrest history, assessed the extent to which a diagnosis of schizophrenia
was predictive of criminal violence among 2 cohorts of patients admitted
to a New York State facility, one in 1968 (N = 255) and the other in 1978
(N = 327) (36). Data were obtained for violent crimes (murder, manslaughter,
rape, attempted rape, kidnapping, and sodomy) for 11 years following the
index admission. Prior arrest history significantly correlated with violent
crime in both cohorts. For those without prior arrest, diagnosis did not
predict subsequent violent crime. Similarly, Wessely and others demonstrated
a slightly increased risk of criminality among those patients with schizophrenia
(37). However, the much larger effects of prior criminality and substance
abuse overshadowed this increase.
Finally, the study by Buckley and others draws attention to and provides
information on the likely target of violence (38). These authors studied
698 patients who were diagnosed with schizophrenia and admitted to a psychiatric
inpatient department between 1983 and 1988. Patients with a history of
violence were found to be similar to those without such history with respect
to positive or negative symptomatology or family history of mental illness.
Sixteen percent of these patients, mostly males, had engaged in a physically
violent or destructive (to property) act since the onset of their illness.
Most of the incidents of community violence occurred in the home and involved
episodes of damage to furniture or assaults on relatives.
Studies of Offenders
Studies of mental illness among offender populations include those that
have estimated the prevalence of mental conditions in incarceration settings,
analytical studies of mental disorder and violence, and follow-up of offenders
released to the community.
Prevalence Studies in Institutions. Two Canadian studies provide compelling
evidence that a significant proportion of incarcerated persons suffer from
substance abuse disorders and serious mental illness. In a study at the
Remand Centre in Edmonton, Bland and others, on a sample of 180 inmates,
found a lifetime prevalence of any psychiatric disorder of 92% and, in
descending order, substance abuse 87%, antisocial personality disorder
57%, affective disorder 23%, and schizophrenia 2% (39). This systematic
sample was obtained from males in custody at the Remand Centre in Edmonton
who were examined by lay interviewers using the Diagnostic Interview Schedule
(DIS). The larger than usual proportion of antisocial personality disorders
found in this study may have been a function of the DIS, which uses information
about criminality in the diagnostic criteria.
In a more recent and larger study, Arboleda-Flórez took a stratified simple
random sample of 1200 admissions to the Calgary Remand Centre (40). Subjects
were examined within the first 24 hours of detention by 4 senior forensic
psychiatrists who used the Structured Clinical Interview for the Diagnostic
and Statistical Manual of Mental Disorders (DSM) (SCID), the Hare Psychopathy
Checklist (PCL), the General Health Questionnaire (GHQ), and other instruments.
A principal diagnosis on either Axis I or Axis II of the DSM-III-R was
made in 728 of the 1200 interviewees (60.7%). The 1-month prevalence was
49.5% for females and 56% for males for an Axis I disorder and 3.6% for
females and 5.5% for males for an Axis II personality disorder. Substance
abuse disorder occurred in 35.7% of women and 47.3% of men. Schizophrenia
was not found among women (possibly because there were fewer women in the
sample) but occurred in 1.2% of males.
Studies showing a high prevalence of substance abusers among incarcerated
offenders also have been reported in the United States (41,42) and the
United Kingdom (43).
Analytical Studies Among Offenders. Very many studies have examined whether
violent criminality can be associated with mental illness or a particular
diagnosis within offender populations. Since most of these studies have
suffered from multiple methodological problems and have yielded inconsistent
results, only the most recent and important ones are reviewed here. Toch
and Adams’ study is the largest (44). These authors used record linkage
technology to study the relationship between mental illness and criminality
in New York State. Computer records of 8379 inmates were matched to New
York State Mental Health services records. Inmates were considered to have
suffered from a mental illness if they appeared in the mental health files.
Of those without a history of mental illness, 13.8% had a history of recent
or remote violence compared with 17% of those with a history of mental
illness or substance abuse. In addition, 5.8% of those with a combination
of mental illness and substance abuse committed unmotivated violent acts
compared with only 1.2% of those without a history of either.
Rice and Harris studied violent recidivism among matched cohorts of 685
persons referred for a brief forensic psychiatric assessment (45). Psychopathy,
schizophrenia, and alcohol abuse were the independent variables. Violent
recidivism occurred in 31% of the subjects. A diagnosis of alcohol abuse
alone or in combination with psychopathy (diagnosed with the PCL) was more
frequently related to violent recidivism. Persons diagnosed with schizophrenia
were less likely to recidivate.
Abram conducted a study aimed at unravelling interactions among alcoholism,
drug abuse, and antisocial personality disorder (46). The study found a
relationship between antisocial personality disorder and 3 levels of prior
criminality (violent crime, felony property crime, and “other” crime [misdemeanours])
and a relationship between substance abuse disorders and 2 levels of prior
criminality (felony property crime and “others”). Intriguingly, this study
did not find an association between alcoholism or “drug disorders” and
criminality, even when controlled for age and comorbid disorders, usually
antisocial personality disorders. This finding echoes the statement made
by Monahan and Steadman that “no relation or, at best, a much weaker relation
is found” between crime and mental disorder when controlling for demographic
and life-history factors (13).
Finally, a Canadian study by Hodgins and Côté examined the relationship
of mental disorder to violent criminality in a representative sample of
461 inmates at a penitentiary in Quebec (47). A total of 107 individuals
were defined as mentally disordered based on DIS diagnoses. These individuals
were not found to have a history of more convictions or more violent convictions
compared with offenders who were not mentally ill.
Community Follow-Up Studies of Offenders. The relationship between mental
illness and subsequent community adjustment among released offenders has
received scrutiny in several studies.
In Chicago, Abram and Teplin were specifically interested in whether persons
with dual diagnoses (mental illness and substance abuse) committed more
violent crimes than those who were not mentally ill but had a history of
drug abuse (48). A random sample of 728 released offenders was followed
for 3 years. Measures of mental illness and substance abuse were collected
using the DIS, and arrest data were obtained from the Chicago Police Department,
the Illinois Bureau of Investigations, and the Federal Bureau of Investigation.
Previous arrests for violent crime and time at risk (number of days out
of jail) were positively associated with subsequent commission of violent
crime. An opiate disorder diminished the probability of future arrest for
violent crime, but the authors point out that their data were collected
prior to the crack-cocaine epidemic in the United States. Mental disorders
(schizophrenia, depression, alcohol abuse) did not predict subsequent arrest
for a violent crime after controlling for age or education.
In a 6-year follow-up of this cohort, the authors studied whether postrelease
arrest rates for violent crime for these same offenders were related to
mental disorder (49). Findings indicated that those persons with schizophrenia
or major affective disorders and with substance abuse had a probability
of 0.43 and 0.46, respectively, for rearrest. In every diagnostic group,
those with a history of violent crime were twice as likely to be rearrested
during the follow-up period compared with those with no history. Although
persons with a history of hallucinations and delusions did not have a higher
probability of subsequent arrest, they did have a slightly higher number
of arrests for violent crimes.
Similar results were reported by Feder, who compared the postprison adjustment
of mentally ill offenders (N = 147) with a group of offenders who were
not mentally ill (N = 400) over a period of 18 months (50). No differences
were noted between the groups when controlling for criminal history. Sixty-four
percent of mentally ill offenders and 60% of not ill offenders were rearrested
at least once during the follow-up; 19% of the mentally ill offenders and
15% of the not ill offenders were rearrested for violent crime.
Epidemiological Community Studies
Police–Citizen Encounters. Because of the considerable discretionary powers
of police, the argument has been made that the rate of arrest of mental
patients in a community is related to deinstitutionalization factors and
the availability of alternatives to incarceration (51,52). In this regard,
Teplin observed a random sample of 283 police officers in their day-to-day
interactions with the public (53). A symptom checklist was used to assess
the presence and severity of psychiatric impairment among those coming
into contact with the police. She found that police encounters with individuals
with a mental disorder occurred infrequently (4% of 2122 person-encounters).
Further, she observed that persons with mental disorders were only slightly
more likely than those without a disorder to be considered suspects in
crime; for those who were considered suspects, the type of crime was not
found to be related to the presence or absence of mental disorder. The
pattern of crime among mentally ill suspects was substantially similar
to the pattern among suspects who were not mentally ill.
Two studies by Holley and Arboleda-Flórez reported similar findings regarding
police–citizen encounters in Calgary (54,55). These studies involved 350
persons who came into contact with the police over a 2-week period. Police
officers were asked to rate observable behaviour of these individuals in
a continuum from normal to severely abnormal. They were then asked to judge
the cause of the abnormal behaviour: alcohol, drugs, mental illness, or
other. The authors found no significant differences in the number or type
of crimes among those rated mentally ill and those assessed to be not mentally
Representative Samples. Several studies have been conducted on representative
samples in the community. Three have used Epidemiological Catchment Areas
(ECA) methodology, characterized by large, representative samples and the
administration of the DIS by lay interviewers. Swanson and others made
use of data from 3 of the 5 sites in the original ECA studies (4). In a
sample of 10 059 subjects, the authors found that more than one-half of
the individuals who reported violent behaviour in the preceding year met
the criteria for a psychiatric disorder compared with only 19.6% among
the nonviolent respondents. Later, Swanson, using the same ECA data, further
tested the hypothesis that the relationship between mental disorder and
violence could be largely explained by the association between alcohol
abuse and violence (56). He found that mental illnesses uncomplicated by
alcohol abuse were associated with some increased risk of violence but
that the large increase in violence among younger males of low socioeconomic
status was largely due to the increased prevalence of alcohol abuse and
comorbidity in this group.
In Edmonton, Bland and Orn used the ECA methodology to study 3 diagnostic
categories among 1200 subjects: antisocial personality disorders, major
depression, and alcohol abuse–drug dependence (5). Altogether, 54.5% of
those with a diagnosis were involved in violent behaviour compared with
15.5% of those without a diagnosis. Persons with 1 or more of these diagnoses
were almost 7 times more likely to be involved with violence than those
without any of these disorders, and the risk of violence was higher among
those with a comorbid alcohol abuse disorder. Of concern, it was noted
that when alcohol was combined with antisocial personality and/or depression,
80% to 93% of these individuals were involved in violence. Both these studies
suggest that the risk of assaultiveness is greater among those who abuse
substances than in those suffering from a major mental illness such as
schizophrenia, affective disorders, or anxiety disorders.
Other Epidemiological Studies. The study by Link and Stueve, previously
discussed, had an advanced methodology: the use of community controls and
the identification of several levels of severity in the measurements (25).
A large record-linkage study in Sweden conducted by Hodgins identified
a birth cohort of 15 117 persons born in 1953 and still residing in Sweden
in 1983 (57). This retrospective historical cohort was followed up for
30 years to determine the proportion of those who had required a psychiatric
admission (N = 603). This group was then compared on criminal variables
with those in the cohort who had never experienced any admissions to a
psychiatric ward or to an institution for the mentally deficient. The results
indicate that, compared with the “normal” controls, men with major disorders
were 4.16 times (95% CI, 2.23–7.78) more likely and women were 27.45 times
(95% CI, 9.80–76.88) more likely to have been convicted of a violence offense.
By far, the most up to date and methodologically sound epidemiological
study of mental illness and violence is that by Steadman and others (58).
This study monitored violence to others at 10-week intervals for 1 year
after discharge among 1136 mentally disordered male and female patients
aged 18–40 years. Patient self-reports were augmented by reports from collateral
informants and by police and hospital records. Members of a comparison
group, consisting of 519 people living in the same neighbourhoods as the
patients, were also interviewed for violent behaviour once every 10 weeks.
The prevalence of violence among patients was not significantly different
from that among members of the control group who had no symptoms of substance
abuse. Substance abuse symptoms significantly raised the rate of violence
in both the patient and the comparison groups, but a higher proportion
of patients reported symptoms of substance abuse. Violence in both patient
and comparison groups was most frequently targeted at family members and
friends and usually occurred at home. The authors concluded that the prevalence
of community violence by people discharged from acute psychiatric facilities
varies considerably according to diagnosis and, particularly, cooccurring
substance abuse diagnosis or symptoms.
On the Matter of Cause
Monahan and Steadman in 1983 pointed out that, when appropriate statistical
controls were applied to factors such as age, race, social class, and previous
institutionalization, relations between crime and mental disorder tended
to disappear (13). For a decade, this statement served as the touchstone
by which mental health providers and scientists alike understood the relationship
between mental illness and violence. Monahan changed this in 1993 when
he stated that, in his opinion, this conclusion may have been premature,
and may well be wrong (14). He reasoned that controlling for factors such
as social class and institutionalization might be wrong because these are
highly related to mental disorder, and the control would attenuate the
relationship between mental illness and violence.
Monahan’s reversal deals with core statistical models, which must be properly
designed and executed for studies to yield data of analyzable quality.
Unfortunately, most studies mentioned above suffer from serious methodological
flaws at the design stage, so even if the data are of good quality, results
may not be properly applicable to a finding of causality. These flaws include
failure to control for confounding factors, selection and misclassification
biases, and failure to appreciate the limitations of the lack of temporal
ordering of factors. In addition, the studies fail to pay attention to
a factor of confounding by definition, brought about by the redefinition
of mental illness in the context of violent behaviours. Harry highlighted
this very important factor in a content analysis of DSM versions in which
he measured the number of times words pertaining to violence against others
or the self were mentioned (59). Harry found that the frequency in the
use of these terms increased from 2.17% in DSM-I to 46.6% in DSM-III.
Link and Stueve have made the point that deficiencies from study to study
tend to cancel each other out, and as such, these studies could be accepted
as indicative of a potential causal relationship: that mental illness causes
violence (60). To address the impact of these deficiencies, however, and
in light of Monahan’s redefinition of factors to consider in a causal relationship
between mental illness and violence, Arboleda-Flórez and others call for
the application of strict epidemiological criteria of causality (61). They
do not agree that deficiencies in studies cancel each other out but rather
that they tend to perpetuate systematic errors and biases from study to
study. Further, they indicate that large discrepancies between statistical
models preclude strong causal inferences until a more detailed etiological
theory that incorporates notions of biological plausibility could be refined
and tested. They also point out that while a recent attempt to articulate
the etiologic model that underlies potential associations between mental
illness and violence has been presented by Hiday (62), this area remains
underdeveloped. Arboleda-Flórez and his collaborators call for stricter
epidemiological criteria to be applied to studies on mental illness and
violence. The criteria are similar to those found in the Report on Smoking
and Health from the Surgeon General of the United States (63). In this
report, the Surgeon General specifies that making judgements concerning
causal mechanisms requires a strict reasoning that goes beyond demonstrated
statistical associations. Similar criteria have been advocated by the Federal
Court of Justice in the Daubert cases on the matter of the alleged teratogenic
effects of Bendectine (64). In their decision, the judges have called for
strict epidemiological criteria as the only type that could be applied
to make statements of causality on risk factors affecting large segments
of the population.
The Risk of Violence
Monahan and Steadman quite accurately identify the risk that a mentally
disordered person will commit harm to be a core issue in mental health
law (65). They advocate for a public health perspective on the issue of
violence; a better concatenation of predictor variables, from clinical
to actuarial; and a concerted, multisite, and synchronized research effort.
On the more technical epidemiological aspects, however, there are also
questions about how to measure the risk. Models that examine the link between
exposures and outcomes in defined populations use as a measure the relative
risk, defined as the ratio of the incidence of persons exposed to a factor
to the incidence of those not exposed to the factor (66). Relative risk
must be calculated from prospective studies because retrospective studies
lack the appropriate denominators describing the populations at risk. In
the case of mental illness and violence, these studies must compare a representative
sample of individuals exposed to the study factor of interest, mental illness,
and at risk of the outcome, violence. Thus, the strongest epidemiological
designs are based on unselected samples, incorporate the passage of time,
include careful measurement of both the exposure and outcome under study,
and make appropriate adjustment of confounding factors. Unfortunately,
the literature review revealed that these methodological requirements have
not yet been met in the study of mental illness and violence.
Yet, when members of the public consider that mental illness causes violence,
they believe that they may suffer harm at the hands of mentally ill individuals.
Although relative risk is used to make statements of causality (that is,
“does mental illness cause violence”?), relative risk is not the best measure
to quantify the risk to the population. Rather, the measure to use should
be the population attributable risk (PAR) defined as the proportion of
all cases that can be ascribed to a factor (67). PAR answers the important
question of how much of the risk in exposed individuals can be eliminated
if the exposure could be reduced or controlled. PAR is used to assess the
potential benefit of preventive efforts and assesses the risks to the population
at large directly and soundly. This measure addresses the sensitive question,
“how much of the violence in the community can be attributed to mental
illness?” Unfortunately, in the literature on mental illness and violence,
only 2 authors mention this issue, and even so, peripherally (37,67).
The review of the literature on mental illness and violence suggests that
1) violent incidents among hospitalized mental patients are committed by
a small minority of patients typically suffering from acute psychotic symptoms
or dementia; 2) formerly hospitalized mental patients may be at a higher
risk of arrest and violence when released into the community, particularly
if they have a history of arrests or violence, or if they experience psychotic
symptoms; 3) substance abuse appears to be a significant risk factor for
violence and criminality among community, patients, and offender populations;
and 4) family members (not the general public) are the most likely targets
of violence by formerly hospitalized patients in the community.
Estroff and others remind us, however, that not all crime committed by
mentally ill persons should automatically be ascribed to the mental illness
(68); contextual factors might have triggered a legitimate response, expected
even from a person without a mental illness. This raises the matter of
stigma and, because research may inform the legislative debate, of the
potential damage to mentally ill individuals and their relatives caused
by poorly designed research in this area of inquiry. Arboleda-Flórez and
others indicate that the many covariations that naturally affect the equation
between mental illness and violence introduce uncertainties in establishing
causality (70). In their opinion, causal inferences are supportable by
the empirical evidence of well-designed and well-executed research only
if no compelling disconfirming evidence can be found. The field is still
far from this goal.
Clinicians, families, legislators, and the public must be aware of the
potential for violence among untreated, deinstitutionalized patients.
Appropriate treatment regimes should be instituted for patients suffering
from acute psychotic symptoms, in or out of the hospital.
Clinicians and families should battle stigmatization due to exaggerated
and unreasonable fears about violence by mental patients.
Studies contain multiple methodological flaws that preclude a judgement
Better, longitudinal, prospective cohort studies are required before definitive
statements can be made.
Population attributable risk to estimate the risk to public health has
not been measured.
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Objectif : Effectuer l’analyse critique de la documentation en matière
de maladie mentale et de violence, examiner si la preuve suffit à établir
un lien causal et fournir des renseignements épidémiologiques pour mesurer
le niveau de risque de la population.
Méthode : D’après une recherche informatisée de la documentation sur la
maladie mentale et la violence menée au préalable pour Santé Canada, on
a procédé à une analyse critique des études en la matière et divisé celles-ci
en trois catégories : 1) les études sur le comportement violent et criminel
chez les patients psychiatriques, 2) les études sur la maladie psychiatrique
chez les contrevenants (études de la prévalence dans les établissements,
études analytiques et suivi communautaire des contrevenants) et 3) les
études épidémiologiques axées sur la communauté sur la question de la maladie
mentale et de la violence (rencontres entre la police et les citoyens,
échantillons représentatifs et autres études épidémiologiques). Les règles
de causalité et les mesures de risque ont ensuite été appliquées à la preuve
Résultats : L’examen de la documentation suggère que seule une infime minorité
des patients hospitalisés, habituellement ceux qui souffrent de symptômes
psychotiques aigus, sont impliqués dans des incidents violents. Les patients
qui ont déjà été hospitalisés sont à risque accru de commettre des actes
violents s’ils ne sont pas traités adéquatement et qu’ils se sentent envahis
par la menace de leurs symptômes psychotiques. Les troubles de toxicomanie
augmentent considérablement le risque de violence. Les membres de la famille
sont les victimes éventuelles les plus à risque.
Conclusions : Il existe une association entre la maladie mentale et la
violence, mais les nombreuses covariations qui influent naturellement sur
l’équation entre les deux facteurs provoquent des incertitudes quant à
A part of this paper is based on Mental Illness and Violence: Proof or
Stereotype?, by J Arboleda-Flórez, H Holley, and A Crisanti, commissioned
by the Health Promotions and Programs Branch of Health Canada.
Manuscript received September 1998.
1Professor and Head, Department of Psychiatry, Queen’s University, Kingston,
Address for correspondence: Dr J Arboleda-Flórez, Hotel Dieu Hospital,
166 Brock Street, Kingston, ON K7L 5G2
Can J Psychiatry, Vol 43, December 1998