Department of Psychological Medicine, Institute of Psychiatry, London
Drugs & Alcohol Research Programme, Research Development & Statistics Directorate, Home Office, London
Department of Psychological Medicine, Institute of Psychiatry, London
National Addiction Centre, Institute of Psychiatry, London
University of Leicester, Section of Social and Epidemiological Psychiatry, Department of Health Sciences, Leicester General Hospital, Leicester
Royal Free and University College Medical School, Department of Mental Health Sciences, London
WHO Collaborating Centre, Institute of Psychiatry, London
Office for National Statistics, London
Correspondence: Dr L.C. Johns, PO67 Department of Psychological Medicine, Institute of Psychiatry, De Crespigny Park, London SE5 8AF, UK. E-mail: ljohns{at}iop.kcl.ac.uk
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ABSTRACT |
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Aims To investigate the prevalence and correlates of self-reported psychotic symptoms using data from the 2000 British National Survey of Psychiatric Morbidity.
Method A total of 8580 respondents aged 1674 years were interviewed. Questions covered mental health, physical health, substance use, life events and socio-demographic variables. The Psychosis Screening Questionnaire (PSQ) was used to identify psychotic symptoms.
Results Of the respondents, 5.5% endorsed one or more items on the PSQ. Factors independently associated with psychotic symptoms were cannabis dependence, alcohol dependence, victimisation, recent stressful life events, lower intellectual ability and neurotic symptoms. Male gender was associated with paranoid thoughts, whereas female gender predicted hallucinatory experiences.
Conclusions Self-reported psychotic symptoms are less common in this study than reported elsewhere, because of the measure used. These symptoms have demographic and clinical correlates similar to clinical psychosis.
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INTRODUCTION |
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METHOD |
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Assessment of psychotic symptoms
In the initial interview, the Psychosis Screening Questionnaire (PSQ;
Bebbington & Nayani, 1995)
was used to assess psychotic symptoms in the past year. The PSQ has five probe
questions (plus secondary questions) enquiring about mania, thought insertion,
paranoia, strange experiences and hallucinations (see Appendix). Respondents
were asked all the items from the PSQ without the usual procedure of cutting
off after a section was answered positively.
For the current analyses, we selected individuals who endorsed one or more psychotic symptom (initial probe plus secondary questions) on the PSQ. Because we wanted to examine psychotic experiences in non-clinical subjects, we first excluded those people with definite or probable psychosis (defined below).
Assessment of psychosis
Four criteria from the first-phase interview were considered likely to be
indicative of psychosis: a self-reported diagnosis or symptoms suggestive of
psychotic disorder; taking anti-psychotic medication; a history of admission
to a psychiatric hospital or ward; a positive response to question 5a of the
PSQ (auditory hallucinations). Respondents who met one or more of these
psychosis screening criteria were selected for a follow-up interview using the
Schedules for Clinical Assessment in Neuropsychiatry (SCAN;
World Health Organization,
1992a). Algorithms then were used to classify respondents
into ICD10 (World Health
Organization, 1992b) psychosis categories. Some people
selected for a second-phase interview could not be contacted or refused a
second interview; in these cases, an assessment of probable
psychosis was assigned to those who scored positively on two or more of
these psychosis criteria.
Correlates
Based on previously reported associations with psychotic symptoms
(Verdoux et al, 1998;
van Os et al, 2000,
2001;
Johns et al, 2002;
Janssen et al, 2003),
the following variables were selected.
Analyses
The data were analysed using the Statistical Package for the Social
Sciences (version 11.0 for Windows). Binary logistic regression analyses were
used to ascertain which factors were associated with the presence of psychotic
symptoms. Associations were expressed as odds ratios (ORs). Sixty people
(0.7%) with probable psychosis were excluded from the analyses, 27 of whom met
the criteria for functional psychosis following a SCAN interview.
We examined the factors associated with the presence of any psychotic symptom (endorsement of initial plus secondary questions on one or more items of the PSQ). First, the predictor variables were entered individually to obtain unadjusted odds ratios. Age was collapsed into three age bands (1634, 3554, 5574). Information about ethnic origin was divided into four groups: White, Black, South Asian and Other. Area of residence was divided into urban and rural. Educational qualifications covered three groups: none, GCSE level, A-level or above. Verbal IQ was estimated from respondents scores on the National Adult Reading Test (NART; Nelson, 1982). Alcohol dependence was classified as present or absent. Drug use was any drug used in the last month (yes/no); and drug dependence was classified as no dependence, dependent on cannabis only or dependent on other drug. Experience of life events and victimisation events was classified dichotomously (yes/no). Second, all the significant variables were entered together to obtain the relative odds of psychotic symptoms controlling for interrelationships between these variables.
We examined whether specific factors were associated with the presence of either paranoid thoughts or hallucinatory experiences. These items were chosen because previous studies have suggested that they are associated with particular risk factors (Johns et al, 2002; Janssen et al, 2003). The response variables selected were Have there been times when you felt that people were deliberately acting to harm you or your interests? and Have there been times when you heard or saw things that other people couldnt? In order to examine specific risk factors, the analyses for each variable included individuals who had endorsed only that item and no other PSQ items.
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RESULTS |
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Socio-demographic distribution of self-reported psychotic symptoms
The frequencies of the variables that were investigated for associations
with psychotic symptoms are shown in Table
2.
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Any psychotic symptom
In the initial unadjusted analysis, the following variables were associated
with the presence of any self-reported psychotic symptom: drug dependence, the
presence of neurotic disorder, drug use, victimisation events, alcohol
dependence, recent stressful life events, non-White ethnic group, younger age,
lower IQ, fewer educational qualifications and urban residence
(Table 3). Gender was not a
significant predictor. In the final model of adjusted odds ratios, neurotic
disorder and drug dependence were the variables most strongly associated with
psychotic symptoms. Individuals were 3.5 times as likely (95% CI
2.94.5) to experience one or more psychotic symptoms if they scored
above 12 on the CISR, were almost three times as likely (95% CI
2.04.4) if they were dependent on cannabis and were just under 2.5
times as likely (95% CI 1.33.9) if they were dependent on any other
drug (with or without cannabis). Experience of victimisation and alcohol
dependence were also strongly associated with psychotic symptoms (OR=2.0, 95%
CI 1.72.6; OR=1.8, 95% CI 1.32.4, respectively). After
controlling for interrelationships between all the variables, young age,
non-White ethnic group, urban residence and recent drug use were no longer
associated significantly with psychotic symptoms.
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Paranoid thoughts
The following factors were independently associated with paranoid thoughts
in a multivariate regression analysis: neurotic disorder, victimisation
experiences, younger age group, alcohol dependence, recent stressful life
event(s), average IQ and male gender (see
Table 4).
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Hallucinatory experiences
The following factors were independently associated with self-reported
hallucinatory experiences in the multivariate analysis: neurotic disorder,
victimisation experiences, average or below-average IQ, alcohol dependence and
female gender (see Table
5).
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DISCUSSION |
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Prevalence of psychotic symptoms in the sample
The annual prevalence of psychotic symptoms, in the absence of psychotic
disorder, was 5.5%. This refers to the percentage of people who endorsed one
or more items on the PSQ, including the secondary questions for the item (i.e.
the more psychotic experiences). As shown in
Table 1, the prevalence was
higher for the less psychotic responses, consistent with the
existence of a continuum of psychotic phenomena in the general population. The
reported figure is lower than the rates of psychotic symptoms reported by
other epidemiological studies (17.5%,
Poulton et al, 2000;
25%, van Os et al,
2000). It is likely that variation in prevalence rates across
studies is partly a consequence of the different instruments used (number and
type of questions asked). The PSQ is a brief measure that assessed only five
psychotic symptoms. One would expect higher prevalence rates with a more
comprehensive measure such as the CIDI, which contains 17 psychotic symptom
items. Also, as we found within the PSQ, questions probing for less
psychotic experiences are likely to be endorsed more frequently. In
addition to differences in the measures, most epidemiological studies have
assessed the lifetime prevalence of psychotic symptoms. This will be much
greater than the annual prevalence, as measured by the PSQ.
Factors associated with any psychotic symptom
There were associations between psychotic symptoms and neurotic disorder,
drug dependence, alcohol dependence, victimisation experiences, recent
stressful life events, lower IQ and fewer educational qualifications. Younger
age group, non-White ethnic group and urban residence no longer significantly
predicted psychotic symptoms after controlling for interrelationships between
predictor variables. In terms of drug dependence, the relationship between
cannabis dependence and psychotic symptoms was the strongest and also may have
contributed to the association between other drug dependence and psychotic
symptoms.
The results from this sample replicate previous findings concerning risk factors associated with psychotic symptoms. Van Os et al (2000) reported an association between neurotic symptoms and all types of psychosis ratings, from not clinically relevant symptoms to clinical psychosis. From our results, it is not possible to know whether neurotic disorder is associated with increased risk of developing psychotic symptoms, or whether it is a consequence of experiencing psychotic symptoms. In a study of adult primary care patients, Olfson et al (2002) found that psychotic symptoms were associated with anxiety, depression and alcohol use disorder, and suggested that the latter were all clinical consequences. On the other hand, neurotic symptoms have been reported in excess in those children who later develop psychosis (Jones et al, 1994; Cannon et al, 2002), and have been identified as part of the initial prodrome in psychosis (Yung & McGorry, 1996). Longitudinal studies have found that adolescent males with neurotic disorders are more likely to develop schizophrenia years later (Weiser et al, 2001), and that neuroticism (which is related to anxiety proneness) increases the risk for subsequent onset of psychotic symptoms (Krabbendam et al, 2002). In a recent review, Freeman & Garety (2003) argue that the frequent occurrence of emotional disorder prior to and accompanying psychosis suggests that neurosis contributes to the development of the positive symptoms of psychosis.
Similarly, we cannot determine the direction of the relationship between cannabis dependence and psychotic symptoms from these data. However, a number of cohort studies have shown that consumption of cannabis is a risk factor for later psychosis (e.g. Andreasson et al, 1987; van Os et al, 2002; Zammit et al, 2002). Thus, Arsenault et al (2002) found that cannabis use in adolescence increased the risk of experiencing schizophrenia symptoms in adulthood, indicating a causal link. Furthermore, this risk was specific to cannabis use, as opposed to the use of other drugs. The association between alcohol dependence and psychotic symptoms may be related to the occurrence of withdrawal symptoms.
Consistent with previous studies (e.g. van Os et al, 2000), lower educational achievement was associated with self-reported psychotic symptoms. The association with potentially threatening life events and victimisation events also corresponds with previously reported risk factors for psychosis. Using the same National Survey data, Bebbington et al (2004) found a high prevalence of reported victimisation among people with psychosis, greater than that found among people with neurotic disorder or drug and alcohol dependence. The association between non-White ethnic group and psychotic symptoms in this study was no longer significant after controlling for other factors, including victimisation and stressful life events. Although it has been reported that Black and ethnic minority patients with psychosis do not experience more life events than do White British patients, they do perceive these events as more threatening (Gilvarry et al, 1999).
Factors associated with paranoid thoughts
Paranoid thoughts were associated with neurotic symptoms, victimisation
experience(s), younger age, alcohol dependence, stressful life events in the
past 6 months, average IQ and male gender. The relationships between paranoia
and victimisation and stressful life events are consistent with cognitive
psychological theories about the development and maintenance of psychotic
symptoms (Garety et al,
2001; Freeman et al,
2002). Thus, experiences of victimisation may lead individuals to
believe that they are vulnerable and to view other people and the world as
hostile and threatening; and stressful events may then trigger symptoms.
Janssen et al (2003)
found that perceived discrimination was associated longitudinally with onset
of delusional ideation. Unfortunately, it is not possible from these data to
determine the precise temporal relationships between victimisation, life
events and paranoia. It could be that subjects with paranoid thoughts have a
biased recall for these experiences, or that the supposedly paranoid thoughts
are actually real, and that people are trying to harm them. Neurotic symptoms
were strongly associated with paranoid thoughts in this sample. Again, this
result is consistent with cognitive models of persecutory delusions
(Freeman et al, 2002),
in which anxiety and depression (particularly anxiety) are thought to play a
central role in the formation of paranoid beliefs.
Factors associated with hallucinatory experiences
Neurotic disorder, victimisation experiences, average and below-average IQ,
alcohol dependence and female gender were associated with hallucinatory
experiences. There was a trend for an association between hallucinations and
Black ethnic group, which replicates the findings of Johns et al
(2002) from an earlier UK
national survey. In that study, the prevalence of hallucinations assessed by
the PSQ in a sample of people of Caribbean origin living in Britain was 2.5
times higher than that in a White sample, although no statistical comparison
was reported. The finding that women were more likely to report hallucinatory
experiences is consistent with the higher rates of hallucinations in females
found in previous studies (Tien,
1991). As with paranoia, the association with victimisation is
consistent with psychological theories of hallucinations, particularly the
link between exposure to trauma and the development of hallucinations
(Romme & Escher,
1989).
Further research
This study found that self-reported psychotic experiences in the general
population were associated with risk factors similar to those commonly
reported for clinical psychosis. Using the interview data from both phases of
the survey, we now intend to compare the correlates of self-reported psychotic
symptoms and clinical psychotic disorder in this sample.
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APPENDIX |
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Hypomania
If yes,
Thought insertion
If yes,
Paranoia
If yes,
Strange experiences
If yes,
Hallucinations
If yes,
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Clinical Implications and Limitations |
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LIMITATIONS
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Received for publication December 22, 2003. Revision received June 1, 2004. Accepted for publication June 26, 2004.
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