Health Services Research Department, Institute of Psychiatry, London
Section of Forensic Mental Health, Department of Psychiatry, Institute of Psychiatry, London
Department of Psychological Medicine, Imperial College, London
Department of Psychiatry, St George's Hospital Medical School, London
School of Psychiatry and Behavioural Science, Manchester Royal Infirmary, Manchester
Section of Forensic Mental Health, Department of Psychiatry, Institute of Psychiatry, London, UK
Correspondence: Dr Paul Moran, Health Services Research Department, Institute of Psychiatry, De Crespigny Park, London SE5 8AF, UK. Tel: 020 7848 0568; fax: 020 7848 0333; e-mail: paul.moran{at}iop.kcl.ac.uk
Declaration of interest P.M. was funded by a Department of Health postdoctoral training fellowship. The UK700 trial was funded by grants from the UK Department of Health and the NHS R&D programme.
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ABSTRACT |
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Aims To examine the association between comorbid personality disorder and violence in community-dwelling patients with psychosis.
Method A total of 670 patients with established psychotic illness were screened for comorbid personality disorder. Physical assault was measured from multiple data sources over the subsequent 2 years. Logistic regression was used to assess whether the presence of comorbid personality disorder predicted violence in the sample.
Results A total of 186 patients (28%) were rated as having a comorbid personality disorder. Patients with comorbid personality disorder were significantly more likely to behave violently over the 2-year period of the trial (adjusted odds ratio=1.71, 95% CI 1.05-2.79).
Conclusions Comorbid personality disorder is independently associated with an increased risk of violent behaviour in psychosis.
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INTRODUCTION |
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METHOD |
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Baseline measures
The presence of comorbid personality disorder was assessed at baseline
using a rapid version of the Personality Assessment Schedule (PASR).
The Personality Assessment Schedule (PAS;
Tyrer et al, 1979) is
a semi-structured interview that measures personality traits and usually takes
30-60 min to complete. The PASR is a direct development of the PAS and
allows for a rapid screen for the presence of ICD10 personality
disorder. It can be completed in approximately 10 min. In a study of 155
patients recruited at one of the UK700 trial centres (St Mary's Hospital,
London), the weighted kappa between the PASR and the full PAS was 0.4,
and sensitivity and specificity were 64% and 82%, respectively, suggesting
that the PASR is a suitable screen for personality disorders
(Tyrer & Cicchetti, 2000;
Van Horn et al,
2000). Scoring for each category of personality disorder on the
PASR is on a three-point scale from 0 to 2, where 0 reflects the
absence of any dysfunction associated with the personality trait, 1 reflects
personality difficulty and 2 reflects personality disorder. The PASR
was administered by an independent research assistant at the end of the
baseline clinical assessment. For the purposes of this study, the PASR
data were regrouped into a dichotomous variable with two categories:
personality disorder and no personality disorder. (Personality disorder was
defined as a PASR score of 2 on any personality disorder category.)
Other information recorded at baseline included:
The following additional information was recorded at baseline: duration of illness, use/misuse of drugs, history of conviction for violent offences and history of special needs education. All baseline and outcome assessments were conducted by senior trainee psychiatrists or psychology graduates who were independent of clinical care.
Outcomes and follow-up
The outcome of interest for the current study was physical assault in the 2
years of the trial. Three data sources were combined to produce a binary
outcome measure for each patient. A positive score on any of these sources
indicated a positive score for assault. The frequency and seriousness of
assault were not recorded. First, patients were asked whether they had
physically assaulted anyone in the 2-year period
(World Health Organization,
1992b). Where an interview with a participant was not
possible, an attempt was made to complete the record with information from a
carer. Second, case managers were interviewed in person or by telephone and
asked about any physical assault committed by their patients. Third, case
notes at all sites were inspected individually for evidence of physical
assault. Home Office criminal records also were obtained for all
participants.
Power calculation
The study was a secondary analysis of the UK700 data-set; 22% of the UK700
study population committed an assault over the study period
(Walsh et al, 2001).
The prevalence of comorbid personality disorder in samples of UK patients with
severe mental illness has been estimated previously to lie between 30 and 40%
(Cutting et al, 1986;
Pilgrim & Mann, 1990).
Assuming either a 30% or a 40% prevalence of comorbid personality disorder in
the UK700 population, the original trial with 700 patients would be able to
detect a 10% increase in total violence in the group with a comorbid
personality disorder as statistically significant at the 5% level with a high
probability (power > 80%).
Statistical methods
Analyses were performed using Stata version 7
(StataCorp, 1999). A strategy
for the statistical analysis of the association between comorbid personality
disorder and violence was drawn up prior to inspecting the data. The data
initially were inspected to examine the baseline demographic characteristics
of the study sample. A check was performed for missing values to examine
whether any biases had been introduced. Participants with missing values for
the relevant variables were excluded from the analysis.
Univariate associations between comorbid personality disorder and other
baseline measures were examined using 2-tests (categorical
variables), t-tests (normally distributed continuous variables) and
MannWhitney tests (skewed continuous variables). Stratified analyses
and logistic regression were then used to examine the association between
personality disorder and assault in more detail. The first logistic regression
model included only personality disorder as an explanatory variable and
assault over the 2 years of the trial as the outcome. The second model
included socio-demographic variables and also the randomisation status of
participants. Variables that have already been shown to predict violent
behaviour in psychosis were then entered into a series of separate regression
models in order to examine further sources of confounding. The final model
also included the baseline clinical status of the participants.
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RESULTS |
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Baseline characteristics of patients with comorbid personality
disorder
Of the 670 patients who were examined with the PASR, 186 were scored
as having a comorbid personality disorder, giving an overall prevalence of 28%
(95% CI 24-31). The prevalence of individual ICD10 sub-categories of
personality disorder is displayed in Table
1. The most prevalent category was schizoid personality disorder,
although patients usually qualified for more than one sub-category of
personality disorder (mean number of personality disorders per patient=1.9,
s.d.=1.2).
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Baseline characteristics of the study sample, by personality disorder status, are given in Table 2. A larger proportion of patients with personality disorders had a previous history of violence and special education and they also had higher mean baseline CPRS and DAS scores and a greater number of unmet needs.
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Effect of personality disorder on violence at 2 years
Information on assault was available for all patients from at least one
data source. Of the 708 patients enrolled in the trial, 158 (22%) committed an
assault over the 2 years of the study
(Walsh et al, 2001).
Of the 670 patients who had baseline personality assessments, 32%
(n=60) of the patients with comorbid personality disorders committed
an assault compared with 19% (n=94) of those without comorbid
personality disorders (2=12.5; P<0.001). Following
adjustments for age, gender, social class, ethnicity and randomisation status,
the following sub-categories of personality disorder were significantly
associated with violence at 2 years: paranoid (adjusted odds ratio=1.36; 95%
CI 1.01-1.84), dissocial (adjusted odds ratio=1.66; 95% CI 1.19-2.31) and
impulsive (adjusted odds ratio=1.45; 95% CI 1.08-1.95). Other sub-categories
of personality disorder failed to reach significance in this model. Fully
adjusted models of associations between paranoid, dissocial and impulsive
personality disorder and violence were not significant.
The effect of comorbid personality disorder on violence during the 2 years of the trial after adjusting for potential confounders is shown in Table 3. Personality disorder was significantly associated with an increased risk of violence after adjusting for baseline clinical state and other established risk factors for violence in the data-set (adjusted odds ratio=1.71; 95% CI 1.05-2.79).
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DISCUSSION |
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Methodological considerations
Assessment of premorbid personality
Assessing the premorbid personality of patients with psychosis is a
formidable task. The presence of an abnormal mental state can easily distort
the assessment, leading to an overreporting of personality pathology. In this
study, the assessment of personality disorder was carried out after the
psychotic illness had been established and this may have led to distortions in
the assessment of some patients' personalities. Although not immune to the
problem of mental state biasing the assessment of premorbid personality, the
PASR incorporates frequent reminders that the questions refer to the
patients' normal selves and not just what they are like when
ill. In addition, the prevalence of personality disorder found in this study
(28%) is lower than that reported in other UK studies
(Cutting et al, 1986;
Pilgrim & Mann, 1990),
suggesting that the degree of overdiagnosis of personality disorder is less
than that occurring in these other studies. Nevertheless, it still remains
likely that some patients in this study were misdiagnosed with a comorbid
personality disorder.
An abbreviated version of the PAS was used to assess personality status in view of the short time available for assessment at the end of a long baseline interview. The PAS was developed originally on a mixed sample of psychiatric patients (Tyrer et al, 1979) and, like other interview schedules for personality disorder, it has not been validated formally for use with pure samples of patients with psychosis. However, given the strength of evidence showing that personality disorder is a major prognostic indicator in mental illness, it was felt important to incorporate an assessment of this into the trial. The PAS is one of the few instruments that attempts to record premorbid personality either before the onset of psychosis or at times of remission, and it has been used in previous studies of personality disorder in psychosis (Tyrer et al, 1994; Cuesta et al, 1999; Gandhi et al, 2001).
Thirty-eight individuals did not have personality ratings and this will have affected the prevalence of comorbid personality disorder in the study sample. If all those not rated by the PASR had a comorbid personality disorder, then the prevalence of comorbid personality disorder in the sample would have risen to 32%. If all those not rated by the PASR had not had a comorbid personality disorder, then the prevalence of comorbid personality disorder in the sample would have fallen to 26%. Hence, the true sample prevalence of comorbid personality disorder must lie between 26% and 32%.
Grouping of personality disorder data
Participants were grouped according to whether they belonged to any
category of personality disorder or not. This dichotomous grouping of patients
is supported by the fact that, in keeping with other studies, the patients in
this study often qualified for more than one sub-category of personality
disorder diagnosis. However, the ICD10 group of personality disorders
consists of eight different sub-categories of disorder, some of which are more
strongly associated with violence than others. In this study, paranoid,
impulsive and dissocial personality disorders were found to be significantly
associated with violence, after adjusting for age, gender, social class,
ethnicity and randomisation status. However, fully adjusted models of the
association between these sub-categories of personality disorder and violence
were not significant and it is likely that these subgroup analyses were
underpowered (type II statistical error). Other categories were not
significantly associated with violence and, although this may also reflect
type II error, evidence linking other categories of personality disorder with
violent behaviour is slender. Indeed, for some categories (anxious and
dependent personality disorder), there is likely to be an inverse relationship
with violence (Gandhi et al,
2001). The grouping of personality disorder data, therefore, will
have masked important behavioural differences between sub-categories and will
have led to a degree of information bias.
Measure of violence
The outcome variable used in this study was a multiple combined measure for
physical assault. Such measures for violence have been found to be superior to
single sources of information (Walsh
et al, 2001). However, we were unable to examine whether
comorbid personality disorder increases the risk of serious assaults in
psychosis, as neither seriousness nor frequency of assault was recorded in the
trial. Finally, participants were recruited from inner-city locations and
therefore the results may not be generalisable to other settings. However, the
multi-centre design, with over 600 patients, should increase the external
validity of the study.
Explanations for an association between comorbid personality disorder
and violence in psychosis
In light of the above methodological considerations, the finding that
patients with comorbid personality disorder had an increased risk of violence
over the 2-year study period could have two possible explanations.
Confounding
First, the increased risk of violence with comorbid personality disorder
might be explained by confounding from other variables associated with
violence. However, after adjusting for special education, victimisation, drug
use and previous violence (all of which have been found to predict violence),
the presence of comorbid personality disorder still remained a significant
predictor of future violence. The multivariate analyses showed some evidence
of confounding by baseline clinical status (symptoms, unmet needs and
disability). However, even after adjusting for this in the model, the
association between comorbid personality disorder and violence remained
statistically significant. The PASR assessments in this study therefore
were likely to have been assessing premorbid personality status rather than
the consequences of mental illness, and this conclusion is supported elsewhere
(Gandhi et al,
2001).
Abnormal premorbid personality: a risk factor for psychosis and later
violence?
The second explanation for our findings is that some patients with severe
mental illness are at higher risk of behaving violently as a direct
consequence of abnormal premorbid personality traits. Epidemiological studies
have found that abnormal premorbid personality is a risk factor for psychosis
(Malmberg et al,
1998). In addition, people with personality disorders
characterised by excessive impulsivity
(Dolan et al, 2001) or
multiple Axis II diagnoses are at higher risk of behaving aggressively
(Coid et al, 1999). It
is therefore conceivable that, for some individuals, abnormal premorbid
personality acts as a common risk factor for both psychosis and later
violence. We are unable to confirm the precise temporal sequence with these
data but our findings strongly indicate that the routine assessment of
premorbid personality can only enhance the assessment of longer-term risk of
violence in patients with psychosis. Key risk prediction tools such as the
Historical Clinical Risk 20 (HCR20;
Webster et al, 1997)
and the Psychopathy Checklist Review (PCLR;
Hare, 1991) incorporate
personality factors among their predictive variables. Indeed, the presence of
personality disorder has been described as one of the variables most strongly
predictive of future violence in samples of patients with mental disorders
(Monahan et al,
2001). Our findings support the importance of this in a large
sample of community-dwelling patients with psychosis.
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Clinical Implications and Limitations |
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LIMITATIONS
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ACKNOWLEDGMENTS |
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The authors thank two anonymous referees for their helpful comments on an earlier draft of this paper.
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Received for publication May 31, 2002. Revision received September 26, 2002. Accepted for publication October 10, 2002.
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