VOL 22, NO. 1, 1996
Schizophrenia and
Homicidal Behavior
by Markku Eronen, Jarl
Tllhonen, and Panu Hakola
Abstract
It is generally thought that schizophrenia does not predispose
subjects to homicidal behavior.
However, many previous studies
have suffered from notable methodological weaknesses. In particular, obtaining comprehensive
study groups of violent offenders
has been difficult. Finnish police
have been able to solve about 97
percent of homicides during the
last few decades. Because most
homicide offenders are subjected
to intensive forensic psychiatric
examination, we were able to obtain data for 93 homicide offenders with schizophrenia among
1,423 arrested during a 12-year
period. Calculations of the odds
ratios revealed that the risk of
committing a homicide was
about 10 times greater for schizophrenia patients of both genders
than it was for the general population. Schizophrenia without
alcoholism increased the odds
ratio more than 7 times; schizophrenia with coexisting alcoholism more than 17 times in
males.
Schizophrenia Bulletin, 22(1):
83-89, 1996.
The media have always been interested in the relationship between
violent behavior and major mental
disorders. Stories of insane homicide offenders, both real and fictitious, are among the most popular in the entertainment business.
Despite the threat to public health,
assessing the risk of violent behavior has been difficult. One of
the main problems in research on
violence is that mild offenses are
not detected by the police, and a
significant proportion of even the
83
most serious violence remains unsolved. In the United States, for
example, more than 30 percent of
all homicide offenders have remained undetected (International
Criminal Police Organisation; Statistics Centre 1991).
Some recent studies have contradicted the earlier view that
major mental disorders do not expose subjects to violent behavior
(Link et al. 1992; Monahan 1992;
Hodgins 1993). Data obtained from
a Swedish birth cohort indicates
that men with major mental disorders are four times more likely
than men with no disorder or
handicap to commit a violent
offense. The corresponding risk
for females is 27 times greater
(Hodgins 1992). The relative risk
of criminal offense among people
with schizophrenia compared with
the general Swedish population
has been reported to be 1.2 times
greater for men and 2.2 times
greater for women (Lindqvist and
Allebeck 1990). Another study by
Lindqvist has revealed that in 20
out of 64 homicide cases (31%) the
offender was considered to be
mentally ill or suffering from a
brain lesion (Lindqvist 1986). C6t<§
and Hodgins have reported that
11 out of 87 (12.6%) male homicide offenders in Quebec's penitentiaries suffered from schizophrenia
(Cote and Hodgins 1992). In Denmark, a study with a followup
period of more than 25 years
demonstrated that 20 percent of
male and 44 percent of female
homicide offenders had a diagnosis
of psychosis (Gottlieb et al. 1987).
Reprint requests should be sent to
Dr. M. Eronen, Dept. of Forensic Psychiatry, University of Kuopio, Niuvanniemi Hospital, FIN-60240, Kuopio,
Finland.
SCHIZOPHRENIA BULLETIN
84
Recent data from a study of incident cases of schizophrenia in the
London Borough of Camberwell
between 1964 and 1984 (Wessely
et al. 1994) revealed that the disease is associated with an increased hazard of acquiring a
criminal record. In this study, men
with schizophrenia were found to
be 3.8 times more likely to commit
violent offenses. Our own preliminary data from a 1-year period
showed a significant association
between some specific mental disorders and homicidal behavior
(Tiihonen et al. 1993). In this article we present data from a comprehensive 12-year study that reveals a significant association
between schizophrenia and homicide risk.
Methods
In Finland, 1,476 murders and
manslaughters were committed between January 1, 1980, and December 31, 1991. (As of December
31, 1990, the Finnish population
was 4,998,478, of which 1,933,000
men and 2,101,000 women were
over age 15 [Statistical Yearbook of
Finland; Statistics Centre 1992].)
The Finnish police were able to
identify 1,428 offenders (criminality
known to the police, 1980-1991;
Statistics Centre 1991). We estimated that the male/female ratio
was the same in the 48 (1,4761,428 •• 48) unsolved homicides as
in the solved cases. Using this assumption and excluding the 53 offenses committed by the same person (50 males and 3 females), we
arrived at totals of 1,302 male and
121 female homicide offenders.
In Finland, almost all homicide
offenders are examined by at least
one psychiatrist to determine if a
thorough forensic psychiatric ex-
amination is required. These examinations include an exhaustive
psychiatric evaluation, standardized
psychological tests such as the
Wechsler Adult Intelligence ScaleRevised (Wechsler 1981) the
Rorschach (Erdberg and Exner
1984), and the Minnesota Multiphasic Personality Inventory
(MMPI; Hathaway and McKinley
1943), evaluation of physical condition with laboratory tests (blood
tests, electroencephalography, and,
in some cases, computed tomography of the head), and 4 to 8
weeks of observation by hospital
staff. All these reports are filed by
the National Board of MedicoLegal Affairs of Finland. During
our 12-year sample period, 3,292
forensic psychiatric examinations
were made, 93 of homicide offenders with schizophrenia.
DSM-III-R (American Psychiatric
Association 1987) classification has
been used in Finland since 1987.
Before that, diagnoses in forensic
psychiatric reports were based on
DSM-III (American Psychiatric Association 1980) or ICD-8 (World
Health Organization 1967) classifications. The reports were systematically checked for DSM-III-R
schizophrenia criteria. In six cases,
the forensic psychiatrist had described the mental disorder and
estimated the criminal responsibility of the offender, but had not
presented the diagnosis. Since
these six cases fulfilled the diagnostic criteria of schizophrenia,
they were included in our index
group. One case, in which there
were too few facts in the forensic
psychiatric report for a definite
schizophrenia diagnosis, was omitted. Checking the reports also revealed that when psychiatrists had
diagnosed major mental disorders
such as schizophrenia, secondary
diagnoses had not always been
presented. If the DSM-III-R criteria for alcoholism were clearly described in the forensic psychiatric
reports, the diagnosis of alcoholism
was included (13 cases), even
though forensic psychiatrists had
not presented this secondary
diagnosis.
About two-thirds of all patients
in Finland found not guilty by
reason of insanity have been
treated in Niuvanniemi, a highsecurity hospital. Sixty-four (68.8%)
of the offenders in our sample
had been or were still in Niuvanniemi. One additional offender
with schizophrenia who had committed his homicide during our
sample period was found in the
hospital files. No forensic psychiatric examination had been performed on him after his second
homicide because he undoubtedly
had schizophrenia. This man had
committed his first homicide in
1952 and had been treated in the
hospital since then.
About 30 percent of the homicide offenders were not studied by
a forensic psychiatrist, and these
were considered not to have schizophrenia in our calculations. These
offenders consisted of those whom
police had not been able to identify (48 cases, 3.4%, assuming that
all the unsolved homicides were
committed by different offenders),
those who committed suicide immediately after their index crime,
and those whom Finnish courts of
law did not consider to be in the
need of a thorough forensic psychiatric examination.
Odds ratios were calculated
using estimates based on the
1-month point prevalence estimates
for DSM-III disorders obtained
from a large U.S. epidemiologic
catchment area study (Regier et al.
85
VOL. 22, NO. 1, 1996
1988), a study of the prevalence of
psychiatric disorders in patients
with alcohol and other drug problems in Canada (Ross et al. 1988),
and a study of substance abuse
among schizophrenia patients in
New York (Dixon et al. 1991). The
Finnish prevalence figures do not
differ notably from the figures
from these studies (Lehtinen et al.
1993).
Results
Of 1,423 homicide offenders during
a 12-year period, we found 86
men and 7 women with schizophrenia. Odds ratios, 95 percent
confidence limits, and p values are
presented in table 1. Schizophrenia
increased the odds ratio of committing homicides by about tenfold
among both genders. Schizophrenia
without alcoholism increased the
odds ratios by about sevenfold
among men, and schizophrenia
with alcoholism by about seventeenfold. The corresponding ratios
for women were about fivefold for
schizophrenia without alcoholism
and more than eightyfold for
schizophrenia with alcoholism. The
prevalence of subforms of schizophrenia and the secondary diagnoses of alcoholism are presented
in table 2. About 50 percent of the
homicide offenders with schizophrenia suffered from the paranoid
form. The undifferentiated form of
schizophrenia was diagnosed in
22.6 percent of the offenders, the
schizoaffective form in 11.8 percent, and hebephrenic form in 10.8
percent. Forty-one of our 93
offenders were also alcoholics.
88
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sessment of homicidal behavior
with a comprehensive sample to
reveal the association of schizophrenia and homicidal behavior,
which has been denied in some
previous studies (Kaplan and
Sadock 1989). In this 12-year sample we were able to confirm our
earlier results about the statistical
risk increase obtained from a
1-year sample (Tiihonen et al.
1993). Calculations were based on
the assumption that offenders with
insufficient data did not have
schizophrenia. The fact that almost
all homicide offenders in Finland
are examined by at least one psychiatrist guaranteed that a forensic
psychiatric evaluation would be
performed on almost all those
with schizophrenia. Nonetheless,
we may have missed a few cases
in which the offender committed
his homicide in a mental hospital
while being treated for well-documented schizophrenia. In some
rare cases, Finnish courts of law
may not ask for thorough forensic
psychiatric evaluation if it is evident that the offender will be
found not guilty by reason of insanity. Also, we did not have access to offenders who committed
suicide immediately after their violent act. Figures were calculated as
if none of the unsolved homicides
committed during our sample period (48 of 1,476) could be attributed to people with schizophrenia.
Because of the above assumptions,
the odds ratios presented must be
regarded as minimum numbers.
All diagnoses were based on
exhaustive clinical examinations
supported by standardized psychological tests, detailed data on the
offender's anamnesis, and observation by hospital staff. Finland's
legal system also requires that
forensic psychiatric reports follow
87
VOL. 22, NO. 1, 1996
semistandardized form. If it were
possible to control the nation's legal system for scientific purposes
for more than a decade, better interrater reliability could have been
achieved. Such a task is very difficult if not impossible in any nationwide study lasting many years,
however.
Because there are no detailed
DSM-III-R classification-based
prevalence rates from Finnish samples, we have used point prevalence rate estimates from U.S.
residents in our calculations. Although the point prevalence of
schizophrenia would be slightly
different in Finland, the data presented here clearly demonstrate
the increased risk of homicidal behavior among schizophrenia patients. We also had to use figures
from the United States and Canada when calculating data on
schizophrenia and comorbid alcoholism (Regier et al. 1988; Ross et
al. 1988; Drake et al. 1990; Mueser
et al. 1990; Dixon et al. 1991),
since no accurate Finnish prevalence data exist. The prevalence
rates for alcoholism among people
with schizophrenia show great
variability, however. The rates
used in our calculations may be
inaccurate, but they are the best
available. Because drug abuse in
Finland is less common than in
the United States or Canada, alcoholism may be a more common
comorbid disorder with schizophrenia in Finland than in these countries. If so, the calculated odds
ratios for people with schizophrenia without alcoholism in Finland
would be respectively greater and
odds ratios for those with coexisting alcoholism, smaller.
Currently, there are many different hypotheses about the relationship between psychiatric disor-
ders and alcoholism. We believe
evidence suggests that substance
abuse is more common among
schizophrenia patients than in the
general population (Regier et al.
1990). The role of possible comorbid personality disorders makes
this relationship even more complex. The figures presented here
have been calculated under the assumption that schizophrenia is the
main disorder and substance abuse
is secondary. In any case, the
odds ratios for homicidal behavior
remain significantly higher even
among schizophrenia subjects without alcoholism than in the general
population. In fact, if one wishes
to examine the issue in this way,
a relevant control would be a general population without alcoholism,
which would again raise the odds
ratios of homicidal behavior
among the examination group of
nonalcoholic schizophrenia subjects.
Our results indicate a dear increase in the odds ratios for homicidal behavior among people with
schizophrenia. Because of the retrospective nature of this study, the
risk increase detected cannot be
regarded as a causal factor. Further longitudinal followup studies
are needed to examine the possible causal association between
schizophrenia and homicide. Our
data also suggest that alcoholism
is an important comorbid disorder
with schizophrenia in Finnish
homicides. The highest odds ratios
of the present study were observed among female schizophrenia
subjects with comorbid alcoholism.
Our results also indicate that
paranoid and schizoaffective forms
of schizophrenia are overrepresented among homicide offenders,
compared with previous data on
the prevalence of the subforms of
schizophrenia (Salokangas et al.
1987). The small number of
offenders with schizophreniform
psychosis is also notable. This
could be due at least in part to
the timing of forensic psychiatric
examinations. Because of bureaucratic delay, these examinations are
usually made about 6 months after
offenders have committed their
acts. This delay can in some cases
confirm the schizophrenia diagnosis instead of less severe diagnoses such as schizophreniform
psychosis.
We have had an advantage in
studying the relationship of mental
illness and homicide under conditions that are much more simple
than those in, for example, the
United States. Our study group
covered the entire country; the
overall clearance rate of homicide
in Finland has been extremely
high; Finland is a racially and socially homogeneous country; and
the role of drug or gang violence
in homicides has remained insignificant. Our results cannot be directly applied to the United States,
where crime rates, because of the
extent of illegal drug use and the
prevalence of organized crime, are
higher than in Finland. Our results
do indicate that schizophrenia per
se is statistically associated with
homicidal behavior, however. Still,
we wish to point out that most
people with schizophrenia cannot
be considered dangerous, though
the risk of homicidal violence is
remarkably high among some
minor subgroups of schizophrenia
patients. We think that it is essential for psychiatrists to learn to
identify these potentially violent
subjects better, so society can focus
limited violence prevention resources on these high-risk offenders. At the moment, a notable
amount of evidence supports the
SCHIZOPHRENIA BULLETIN
88
idea that psychotic symptoms,
such as persecutory themes, may
lead to violence (Link et al. 1992;
Krakowski and Czobor 1994).
References
American Psychiatric Association.
DSM-III: Diagnostic and Statistical
Manual of Mental Disorders. 3rd
ed. Washington, DC: The Association, 1980.
American Psychiatric Association.
DSM-III-R: Diagnostic and Statistical Manual of Mental Disorders. 3rd
ed., revised. Washington, DC: The
Association, 1987.
Cote", G., and Hodgins, S. The
prevalence of major mental disorders among homicide offenders.
International Journal of Law and
Psychiatry, 15:89-99, 1992.
Dixon, L.; Haas, G.; Weiden, P.;
Sweeney, J.; and Frances, A. Drug
abuse in schizophrenic patients:
Clinical correlations and reasons
for use. American Journal of Psychiatry, 148:224-230, 1991.
Drake, R.E.; Osher, F.C.; Noordsy,
D.L.; Hurlbut, S.C; Teague, G.B.;
and Beaudett, M.S. Diagnosis of
alcohol use disorders in schizophrenia. Schizophrenia Bulletin,
16(1)57-67, 1990.
Erdberg, P., and Exner, J.E.
Rorschach assessment. In: Goldstein, G., and Hersen, M., eds.
Handbook of Psychological Assessment. New York, NY: Pergamon
Press, 1984. p. 332.
Gottlieb, P.; Gabrielsen, G.; and
Kramp, P. Psychotic homicides in
Copenhagen from 1953 to 1983.
Acta Psychiatrica Scandinavica,
76:285-292, 1987.
Hathaway, S.R., and McKinley, J.C.
The Minnesota Multiphasic Person-
ality Schedule. Minneapolis, MN:
University of Minnesota Press,
1943.
behavior of mental patients reconsidered. American Sociological Review, 57:275-292, 1992.
Hodgins, S. Mental disorder, intellectual deficiency, and crime. Archives of General Psychiatry, 49:476483, 1992.
Monahan, J. Mental disorder and
violent behavior: Perceptions and
evidence. American Psychologist,
47:511-521, 1992.
Hodgins, S. Mental Disorder and
Crime. London, England: Sage Publications, 1993.
Mueser, K.T.; Yamold, P.R.; Levinson, D.F.; Singh, H.; Bellack, A.S.;
Kee, FC; Morrison, R.L.; and
Yadalam, K.G. Prevalence of substance abuse in schizophrenia:
Demographic clinical correlates.
Schizophrenia Bulletin, 16(l):31-56,
1990.
International Criminal Police
Organisation. International Crimes
Statistics, 1989-1990. Lyon, France:
The Organisation, 1991.
Kaplan, H.J., and Sadock, B.J. Comprehensive Textbook of Psychiatry.
5th ed., Vol. 1. Baltimore, MD:
Williams & Wilkins Company,
1989. p. 765.
Krakowski, M.J., and Czobor, P.
Clinical symptoms, neurological
impairment, and prediction of violence in psychiatric inpatients. Hospital and Community Psychiatry,
45:700-705, 1994.
Regier, D.A.; Boyd, J.H.; Burke,
J.D.; Rae, D.S.; Myers, J.K.;
Kramer, M.; Robins, L.N.; George,
L.K.; Karno, M.; and Locke, B.Z.
One-month prevalence of mental
disorders in the United States:
Based on five epidemiologic catchment area sites. Archives of General
Psychiatry, 45:977-986, 1988.
Lehtinen, V.; Veijola, J.; Lindholm,
T.; Vaisanen, E.; Moring, ].; and
Puukka, P. Stability and Changes of
Mental Health in the Finnish Adult
Population, [in Finnish] Turku, Finland: Kansanelakelaitoksen
julkaisuja, AL-sarja, 1993.
Regier, D.A.; Farmer, M.E.; Rae,
D.S.; Locke, B.Z.; Keith, S.J.; Judd,
L.L.; and Goodwin, F.K. Comorbidity of mental disorders with
alcohol and other drug abuse: Results from the epidemiologic catchment area (ECA) study. Journal of
the American Medical Association,
264:2511-2518, 1990.
Lindqvist, P. Criminal homicide in
northern Sweden, 1970-1981: Alcohol intoxication, alcohol abuse and
mental disease. International Journal
of Law and Psychiatry, 8:19-37,
1986.
Ross, H.E.; Glaser, F.B.; and Germanson, T. The prevalence of psychiatric disorders in patients with
alcohol and other drug problems.
Archives of General Psychiatry,
45:1023-1031, 1988.
Lindqvist, P., and Allebeck, P.
Schizophrenia and crime: A longitudinal follow-up of 644 schizophrenics in Stockholm. British Journal of Psychiatry, 157:345-350, 1990.
Link, B.G.; Callen, F.T.; and Andrews, H. The violent and illegal
Salokangas, R.K.R.; Stengard, E.;
Rakkolainen, V.; Helle, J.; and Kaljonen, A. New Schizophrenic Patients and Their Families, [in Finnish] Helsinki, Finland: Foundation
for Psychiatric Research in Finland,
1987.
89
VOL 22, NO. 1, 1996
Statistics Centre of Finland. Criminality Known to the Police, 19801991. Helsinki, Finland: The Centre, 1991.
Wechsler, D. Wechsler Adult Intelligence Scale—Revised Manual. New
York, NY: Psychological Corporation, 1981.
Statistics Centre of Finland. Statistical Yearbook of Finland 1992.
Helsinki, Finland: The Centre,
1992.
Wessely, S.C.; Castle, D.; Douglas,
A.J.; and Taylor, P.J. The criminal
careers of incident cases of schizophrenia. Psychological Medicine,
24:483-502, 1994.
Tiihonen, J.; Eronen, M.; and
Hakola, P. Criminality associated
with mental disorders and intellectual deficiency. Archives of General
Psychiatry, 50:917-918, 1993.
Announcement
World Health Organization. Manual of the International Statistical
Classification of Diseases, Injuries,
and Causes of Death. Vol. I, 8th ed.
Nominations are being sought for
the 1996 American Psychological
Foundation Alexander Gralnick
Award for schizophrenia research.
Candidates for this award of
$2,000 must demonstrate an exceptional contribution to schizophrenia
research with a focus on the discovery and/or treatment of the
earliest signs of schizophrenia,
emphasizing the psychosocial aspects as opposed to the biological
aspects of the disease process.
Geneva, Switzerland: The Organization, 1967.
The Authors
Markku Eronen, M.D., is House
Officer, Jari Tiihonen, M.D., Ph.D.,
is Acting Professor of Forensic
Psychiatry, and Panu Hakola,
M.D., Ph.D., is Emeritus Professor
of Forensic Psychiatry, Department
of Forensic Psychiatry, University
of Kuopio, Niuvanniemi Hospital,
Kuopio, Finland.
Preference will be given to persons
working in a psychiatric facility.
Applications must be submitted
to the American Psychological
Foundation by March 1, 19%. To
request an application or additional information, please contact
Isabelle Puleo
The American Psychological
Foundation
750 First Street, NE
Washington, DC 20002
Telephone: (202) 336-5843