Institute of Psychiatry, London
Department of Mental Health and Alcohol Research, National Public Health Institute, Helsinki
Social, Genetic, and Developmental Psychiatry Research Centre, Institute of Psychiatry, London
University of Cambridge, UK
Institute of Psychiatry, London, UK
Correspondence: Mary Cannon, Division of Psychological Medicine, Institute of Psychiatry, De Crespigny Park, Denmark Hill, London SE5 8AF, UK. Tel: 020 7848 0415; fax: 020 7701 9044; e-mail: m.cannon{at}iop.kcl.ac.uk
Funding detailed in Acknowledgements.
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ABSTRACT |
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Aims To investigate whether such risk factors are associated with criminal behaviour in an epidemiological cohort of patients with schizophrenia.
Method We identified from health care registers all individuals with schizophrenia born in Helsinki between 1951 and 1960, and used the national criminal register to identify those with a criminal record by 1995. Childhood information was obtained from archived birth and school records.
Results Poor educational attainment, poor grades for attention at school, higher birth weight and larger head circumference were significantly associated with the risk of criminal offending in adulthood in this sample of patients with schizophrenia. An association between labour/delivery complications and later violent offending among male patients was of borderline significance.
Conclusions Our hypotheses that birth complications and childhood neuromotor problems would increase the risk of criminal offending in schizophrenia were not upheld.
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INTRODUCTION |
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Background
The association between schizophrenia and violence has received much public
attention in recent years. It has now been demonstrated consistently that male
patients with a diagnosis of schizophrenia are between four and seven times
more likely to commit violent offences than the general population (for a
review, see Walsh et al,
2002, this issue). Because patients with schizophrenia are known
to have more birth complications and neurodevelopmental and intellectual
impairments than controls (Cannon &
Jones, 1996), such factors may be particularly prevalent in the
subgroup of patients who have a propensity to violence. High rates of
neurological problems, particularly poor motor coordination, poor
visuo-spatial function and low IQ, have been found among inpatients with
schizophrenia who have a history of violence
(Krakowski et al,
1989), supporting the notion of neuro-developmental
impairment.
In this study we examined the relationship between birth complications, school functioning and later criminal behaviour in a cohort of Finnish patients with schizophrenia using prospectively collected data. We hypothesised that, among individuals with schizophrenia, offenders would be more likely than non-offenders to have: (a) a history of birth complications; (b) poorer motor coordination skills; and (c) lower educational attainment.
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METHOD |
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Criminal outcome information
Data on criminal convictions to the end of 1995 were obtained from the
Finnish Central Criminal Register, maintained by the Ministry of Justice. A
person gets a criminal record when he/she is sentenced with one of the
following: imprisonment, fine, community service, youth crime or diminished
responsibility due to a mental disorder. Records are deleted from the register
after different time periods, depending on the severity of the penalty.
Records are deleted after 5 years following a suspended sentence of
imprisonment or youth crime. Records are deleted after 10 years for sentences
of a maximum of 2 years of imprisonment or community service. Records are
deleted after 20 years for sentences of more than 2 years of imprisonment or
diminished responsibility due to a mental disorder. Crimes with sentences of
over 5 years in prison stay on the register and are only deleted after the
person dies or reaches 90 years of age. (Information on the Finnish Criminal
Register can be found on the Finnish-language site
http://www.om.fi/148.htm
). As in previous studies (Kandel &
Mednick, 1991; Raine et al,
1994,
1996,
1997), the category of violent
crimes was taken to include homicides, assault, robbery, arson, illegal
possession of a weapon, sexual crime and violation of domestic peace. All
other crimes, including theft, blackmail, fraud and driving offences, were
defined as non-violent.
Obstetric information
There are three large maternity units in Helsinki that have been
established since the 1940s: Naistenklinikka 1 and 2, the maternity
departments of the Central University Hospital of Helsinki, and
Kätilöopisto, a training hospital for midwives. Detailed birth
records have been completed by the midwives using similar standardised forms
for all women who have given birth in these units. These birth records are
stored in the archives of the Helsinki University Central Hospital and the
Helsinki City Archives. The records cover the time from admission to the
maternity unit until discharge: the first section of the birth record gives
demographic information about the mother and a summary of any complications
during the pregnancy; the second section describes the examination of the
mother by the midwife on admission; the third section details the course of
the delivery; and the last section describes the condition of the infant at
birth, including measurements of length, head circumference and birth weight
and the infant's neonatal progress.
Birth record data were entered onto a specially designed computer database, following the standardised format of the records. Three categories of obstetric complications (yes/no coding) were defined for this study: pregnancy complications, labour/delivery complications and neonatal complications. A positive score on the pregnancy complication variable was awarded if the subject had experienced one or more of the following: preeclampsia, eclampsia, diabetes, bleeding, fever, rhesus incompatibility, anaemia. A positive score for labour/delivery complications was awarded if the subject had experienced one or more of the following: breech or foot presentation, forceps delivery, cephalo- pelvic disproportion, Caesarean section, uterine exhaustion, risk of asphyxia, abnormalities of foetal heart rate or rhythm, cord around neck or body, meconium-stained amniotic fluid, cyanosis, resuscitation or incubator required after delivery. A positive score for neonatal complications indicated one or more of the following: convulsions, intraventricular haemorrhage, transfer to special care baby unit, abnormal neurological signs. Other obstetric information such as birth weight, length at birth and head circumference were also extracted from the birth records and were analysed as continuous variables.
School record cards
During the period of this study, more than 95% of children in Finland
attended the state elementary school (kansakoulu) system from the age
of 7 years (Cannon et al,
1999). Children with learning disabilities (1.3-1.9%) or who
suffered from emotional or conduct disorder (0.3-0.8%) were catered for within
the state system in special classes
(Somerkivi, 1977). Children
attended the school that was closest to their home. All children in the state
system studied the same subjects for the first 4 years of schooling. At the
end of Grade 4, when children were aged 11 years, each child was given a
ranking score (sijaluku) based on the results of their summer
examinations. This score helped to determine whether the child went on to high
school (oppikoulu), which gave a more academic education, or remained
at the elementary school for a further 4 years. This paper examines only the
results from the 4 years when all children studied a common programme. The
core curriculum subjects were mathematics, religion, reading,
writing, handcrafts, physical education and music. We recorded the results of
the summer examinations. Marks given for each subject ranged from 4 (fail) to
10 (excellent). All pupils were given marks for conduct and attentiveness each
year, and the number of hours of absence without leave was recorded. Most
children scored 10 for conduct but a mark was deducted for
transgressing school rules.
Social class information
Socio-economic group was defined on the basis of paternal occupation
recorded on the birth records. Four socio-economic groups were identified on
the basis of the City of Helsinki Social Group Classification
(Central Statistics Office,
1971), consisting of: (a) professional, managers and higher
administrative and clerical staff; (b) lower clerical employees; (c) skilled
workers; and (d) unskilled workers. For the purposes of the analysis, these
categories were collapsed into two groups: professional/clerical and
skilled/unskilled workers.
Statistical analysis
Two sets of analyses were carried out: the first set used any criminal
record as the outcome, and the second used violent crimes only as the outcome.
Obstetric complications were grouped into three categories, as defined
earlier: pregnancy, labour/delivery and neonatal complications. Odds ratios
with 95% confidence intervals were obtained for each category of obstetric
complications using logistic regression. All models were adjusted for gender.
Interaction terms with social class were created for each category and added
to the model. Continuous obstetric variables were analysed using one-way
analysis of variance, including gender as a covariate. School results were
analysed using logistic regression, with robust standard errors adjusted for
clustering within subject. All school subjects were entered together into the
regression model, with dummy variables for each year of schooling. All
analyses were repeated using males only to facilitate comparisons with
previous research and to test specific hypotheses relating to males. Logistic
regression was used to examine progression to high school, controlling for
gender and social class. One-way analysis of variance was used to compare mean
rank in class at age 11 years, controlling for social class and stratified by
gender. Statistical analyses were carried out using STATA version 6.0
(StataCorp, 1999). The power
of this study was sufficient to detect an odds ratio of about 2 for the
relationship between birth complications and later criminality, which is the
effect size usually found in general population cohorts (Raine et al,
1994,
1997).
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RESULTS |
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Of our total cohort of individuals with schizophrenia, 9.4% (13.4% of the
males and 4% of females) had a criminal record by 1995, including 4.3%
convicted of violent crimes. There was a significant excess of males among the
offenders (80.3% v. 57.2%; 2=12.2, d.f.=1;
P<0.001) but no significant difference in the social class
distribution. There was no difference between the offenders and the
non-offenders on age at first admission with schizophrenia (26.2 v.
25.1 years; t=-1.5, P=0.14). The proportion of cases with
criminal records was not significantly different among those cases for whom
birth or school records could be found and those for whom they could not be
found.
Obstetric complications
There was no significant relationship between pregnancy or neonatal
complications and later criminality or violence
(Table 1). We tested the
biosocial interaction hypothesis by including interaction terms
between categories of obstetric complications and social class in the models,
but these were not significant. Mean birth weight and head circumference were
higher among offenders than among non-offenders
(Table 2). There was a tendency
for length at birth to be increased among the offenders, but this was not
significant. The findings for head circumference but not birth weight remained
significant when males were examined separately. A post hoc subgroup
analysis, based on the results from the Raine et al
(1994,
1996,
1997) series of studies, found
a modest association between labour/delivery complications and later
conviction for a violent offence among males only, but this finding just
missed statistical significance (Table
1). There was no significant change in the odds ratio (OR) for
this relationship when we adjusted for birth weight (OR=2.05; 95% CI 0.95-4.4;
P=0.067), indicating that the association between high birth weight
and criminal offending is independent of delivery complications. There were no
significant associations between obstetric complications and later criminality
or violence when females were examined separately.
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School performance
Offenders were less likely to progress to high school after the first 4
years of elementary schooling than non-offenders (OR (adjusted for
gender)=0.49, 95% CI 0.25-0.97; P=0.042). Male offenders had lower
rank in their class at age 11 years than male non-offenders (0.34 (0.05)
v. 0.53 (0.02), t=3.2, d.f.=189; P=0.001). When
performance in individual subjects was examined, the most consistent
differences between offenders and non-offenders were on grades for
attentiveness and handcrafts (Table
3). The offenders had significantly lower teacher ratings for
attentiveness than non-offenders, and the odds of later having a criminal
record decreased by about 30% for each increase in the grade for
attentiveness. These differences persisted when violent crimes only were
examined separately and when male subjects were analysed separately. There was
no significant change in the odds ratio for the relationship between
attentional problems and later offending (OR=0.67, 95% CI 0.5-0.9;
P=0.01) when delivery complications, birth weight, length and head
circumference were entered into the regression model, indicating that the
lower score for attentiveness among the offenders is not due to obstetric
factors. In contrast, the offenders scored higher than the non-offenders on
handcrafts and the odds of later having a criminal record increased by 40% for
each unit increase in the grade for handcrafts. There were no significant
differences between the groups for scores in academic subjects, religion or
music or number of days absent from school without permission. There was no
significant difference between the offenders and the non-offenders for teacher
ratings of conduct. None of the offenders and less than 1% of the
non-offenders had ever been deducted marks for conduct (i.e. score of
<10).
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DISCUSSION |
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Rates of criminal offending
In this cohort of individuals with schizophrenia, over 13% of males and 4%
of females had a criminal record by 1995 when aged between 35 and 44 years.
These rates correspond well with results by Brennan et al
(2000), who found that 11.3% of
males with schizophrenia and 2.8% of females with schizophrenia from a Danish
birth cohort ranging between 44 and 47 years in age had a criminal record by
1991. Tiihonen et al
(1997) found that 20.6% of
male patients with schizophrenia in the North Finland 1966 birth cohort had a
criminal record by 25 years of age. The lower rate of criminal offending in
our sample may be due to the older age of our sample and the fact that some
criminal records for less serious offences may have already been deleted from
the register.
Birth complications and later offending
We did not prove our first hypothesis that a history of obstetric
complications increased the risk for later criminal conviction in
schizophrenia nor did we find a biosocial interaction
between obstetric complications and low social class. However, Finland in the
1950s was a rather egalitarian society, and social class based on occupation
did not necessarily correlate with social deprivation or neglect. No direct
measure of maternal rejection as used by other researchers (Raine et
al, 1994,
1997;
Hodgins et al, 2001)
was available in this sample.
Previous work (Tibbetts & Piquero, 1999) has found a relationship between low birth weight and later criminality in the general population. In contrast, we found that, among this sample of individuals with schizophrenia, offenders had significantly higher birth weight and a larger head circumference than non-offenders. We did not have information on maternal smoking during pregnancy, which has been linked to adult violent crime (Brennan et al, 1999; Räsänen et al, 1999), but if such a link had been present in our sample we would have expected lower birth weights among the offenders. We can speculate that higher birth weight predicts larger physique later in life. Raine et al (1998) found that large body size at age 3 years is related to aggression at age 11 years.
Although the association between labour/delivery complications and an increased risk of violent crime among males was not statistically significant, this subgroup analysis did not have sufficient power to discount such a relationship or to test for a biosocial interaction effect. But, in any case, labour/delivery complications only accounted for about 1% of the variance in violent offending in our sample and are thus not a major risk factor for violence in schizophrenia.
Motor coordination and later offending
Contrary to our second hypothesis, we failed to find any association
between later offending and childhood neuromotor problems as indexed by school
performance in sports and handcrafts. In fact, those cases with a criminal
conviction actually performed better at handcrafts in school than cases
without a conviction. This negative finding is unexpected, because a previous
study on this sample found that poor performance in sports and handcrafts was
the most significant predictor of later schizophrenia related to school
performance (Cannon et al,
1999).
Educational attainment and later offending
Individuals with schizophrenia who were later convicted of a criminal
offence had a lower rank in their class at age 11 years and were less likely
to progress to the academic high school than those without a criminal
conviction. This accords with other work showing a history of poor educational
attainment and learning difficulties among patients with schizophrenia who
have a history of offending (Schanda
et al, 1992; Heads
& Taylor, 1997). Offenders had significantly lower ratings for
attentiveness than non-offenders throughout their school career. What is the
possible mechanism for this effect? Neuropsychological studies of antisocial
offenders show attentional problems (Henry
& Moffitt, 1997) and children with attention-deficit
hyperactivity disorder have higher rates of delinquency and adult criminal
convictions (Farrington et al,
1996). Therefore we may, in fact, be detecting comorbid antisocial
personality disorder or childhood attention-deficit hyperactivity disorder.
Arguing against this, however, is the fact that none of the offenders had been
noted as having major conduct problems at school. It is also possible that
poor attentiveness persists into adulthood and this group is merely less good
at being criminal (i.e. more easily detected by the police) than the attentive
group.
Although two out of three of our initial hypotheses were not upheld, our findings lead to further hypotheses regarding, for instance, the possible links between poor attentiveness or higher birth weight and later offending in schizophrenia. The literature in this area should continue to move beyond what is well-established that there is a link between crime and schizophrenia and towards the more interesting question of what mechanism or mechanisms account for this association.
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Clinical Implications and Limitations |
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LIMITATIONS
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ACKNOWLEDGMENTS |
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Received for publication September 10, 2001. Revision received February 25, 2002. Accepted for publication February 25, 2002.
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