Department of Psychological Medicine, Institute of Psychiatry, London
Department of Epidemiology and Public Health, University College London, London
Department of Psychiatry and Behavioural Sciences, Whittington Hospital, London
Department of Psychology, Institute of Psychiatry, London
Correspondence: Dr L. C. Johns, Department of Psychological Medicine, Institute of Psychiatry, De Crespigny Park, London SE5 8AF, UK
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ABSTRACT |
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Aims To examine the prevalence of hallucinations in White and ethnic minority samples using data from the Fourth National Survey of Ethnic Minorities.
Method Interviews of 5196 ethnic minority and 2867 White respondents were carried out. The respondents were screened for mental health problems and the Psychosis Screening Questionnaire asked about hallucinations. Those who screened positive underwent a validation interview using the Present State Examination.
Results Four per cent of the White sample endorsed a hallucination question. Hallucinations were 2.5-fold higher in the Caribbean sample and half as common in the South Asian sample. Of those who reported hallucinatory experiences, only 25% met the criteria for psychosis.
Conclusions The results provide an estimate of the annual prevalence of hallucinations in the general population. The variation across ethnic groups suggests cultural differences in these experiences. Hallucinations are not invariably associated with psychosis.
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INTRODUCTION |
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This study analysed data collected from a national community survey in order to examine the prevalence of hallucinatory experiences in the general population of England and Wales. The analyses addressed three questions: what is the occurrence of hallucinations in this national community sample; do the rates vary across ethnic groups; and to what extent are the reported hallucinations associated with mental health problems?
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METHOD |
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The initial screening stage of the mental health assessment used parts of the revised version of the Clinical Interview Schedule (CISR; Lewis et al, 1992) and the Psychosis Screening Questionnaire (PSQ; Bebbington & Nayani, 1995). Questionnaires were administered by interviewers matched for ethnicity and language. The CISR was used to identify those who possibly had a neurotic disorder, particularly depression, and the PSQ was used to identify those who possibly had a psychotic disorder. The PSQ has questions on hypomania, thought insertion, paranoia, strange experiences and hallucinations. The two hallucination questions are:
Respondents were asked all the questions from the PSQ; the usual system of a cut-off after a section was answered positively was ignored. The survey also asked half of the sample about their use of medication and history of illness. Those respondents who scored positively for symptoms on either the CISR or PSQ were invited for a follow-up interview and underwent a more detailed psychiatric assessment using version 9 of the Present State Examination (PSE; Wing et al, 1974). The interview was undertaken by ethnically and language-matched psychiatric nurses or doctors.
For the current analysis, we examined the frequencies of responses to the two questions asking about hallucinations on the PSQ. We also examined the PSE classification for those respondents who endorsed both PSQ hallucination questions and were followed up. Chi-squared tests were used to investigate possible bivariate relationships between reports of hallucinations and other variables. In the ethnic minority sample, the data from the four South Asian groups were combined (to maximise sample sizes and because there were minimal differences between the individual groups) and the data from the Chinese group were not used (because the sample was too small for independent analysis).
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RESULTS |
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The prevalence of hallucinatory experiences varied across the ethnic groups
(Table 1). Compared with the
White sample, the rates were 2.5-fold higher in the Caribbean sample and
approximately half as common in the South Asian sample. In the Caribbean
sample, the prevalence of hallucinatory experiences was greater in the 20-29
and 50-59 years age groups (Fig.
1). The age distribution of hallucinations in the South Asian
sample was fairly constant. Females reported more hallucinatory experiences
than males in the Caribbean sample (11.8% . 7.4%,
2=7.5,
P=0.006) but there was no gender difference in the South Asian sample
(males: 2.5%, females: 2.1%).
To examine whether rates of hallucinations in the ethnic minority samples
varied by migration, the samples were divided into migrant and non-migrant
groups. Those who were born in Britain or who moved before the age of 11 years
were classified as non-migrants and those who migrated at age 11 years or
older were classified as migrants. In the Caribbean group there was no
difference in the occurrence of hallucinations according to age on migration
to Britain (9.3% . 9.4%). However, in the South Asian group non-migrants
reported significantly higher rates of hallucinations than did migrants (3.7%
. 1.2%,
2=25, P<0.001).
Our third research question concerned the mental health status of those
respondents who endorsed the hallucination questions on the PSQ. From the
questions on medication use and diagnosed illnesses, those who had taken
antipsychotic medication or had a diagnosed psychotic disorder could be
identified. Only a very small percentage of those people who reported a
hallucinatory experience on the PSQ had a psychotic illness according to these
criteria (Table 2). This
percentage was lowest in the Caribbean sample (2=10.2,
P=0.006).
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Of the 89 respondents who endorsed both hallucination questions on the PSQ, 52 were followed up and interviewed using the PSE (26 White, 15 Caribbean and 11 South Asian people). Nine (17%) of these had one or more hallucination symptom on the PSE and five (10%) met the criteria for a hallucination syndrome. In terms of diagnostic class, 13 people (25%) had a psychotic disorder, 29 (56%) had an affective disorder and 10 (19%) did not meet any diagnostic criteria. The percentages with any diagnostic class were similar in the White and Caribbean groups but lower for the South Asian group.
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DISCUSSION |
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The estimated figure is considerably lower than the rates of hallucinations reported by other epidemiological studies. For example, data from the National Institute of Mental Health (NIMH) Epidemiologic Catchment Area Program in the USA showed that the lifetime prevalence of hallucinations in this sample of 18 572 community residents was 10% for men and 15% for women (Tien, 1991). What might account for the low prevalence rate in this study? The figure reported here represents annual prevalence, whereas previous studies have reported lifetime prevalence. The lifetime prevalence of hallucinations in this sample would be higher than 4%, but possibly not the three to four times higher that would be needed to bring it into line with other studies. Prevalence rates are, of course, dependent on the questions asked in the study. The hallucination questions in the PSQ follow a series of questions assessing the possibility of psychosis and may be perceived in this context, reducing respondents' willingness to endorse them. Thus, the stigma associated with mental illness, particularly psychosis, may well reduce the extent to which people self-report. In addition, the first question asks about the occurrence of unusual visual and auditory experiences on more than one occasion (Have there been times when...), and the second question only probes for auditory verbal hallucinations (... hear voices saying quite a few words or sentences...). Hence, respondents may not have reported experiences that occurred infrequently or that they considered irrelevant to the question. The data reported by Tien (1991) were obtained using the broader NIMH Diagnostic Interview Schedule (DIS; Robins et al, 1981). Assessment of hallucinations began with a general symptom question: Have you ever had the experience of seeing/hearing something or someone that others who were present could not see/hear? Positive responses were followed by structured probe questions that inquired about the nature, cause and consequences of these experiences.
Hallucinatory experiences were most commonly reported by 16- to 19-year-olds and the age distribution was similar to that for auditory hallucinations in the Tien study. There were similar prevalence rates for men and women in this White sample, which contrasts with higher rates of hallucinations reported by women in previous studies (Sidgewick et al, 1894; Tien, 1991), although females reported more hallucinatory experiences than males in the Caribbean sample.
Variation across ethnic groups
Reports of hallucinations varied significantly across ethnic groups, with
the highest rates in the Caribbean group (9.8%) and the lowest in the South
Asian group (2.3%). The ethnic differences in prevalence rates raise the
possibility of cultural differences in the experience and reporting of
hallucinations and are in accordance with previous reports of cultural
variation in hallucinatory experiences
(Al-Issa, 1977;
Slade & Bentall, 1988). In
a similar epidemiological study, Schwab
(1977) found that Black
Americans reported a higher frequency of hallucinations than White
respondents, but there was a strong association with religious affiliation in
that sample.
There was no effect of migration on the occurrence of hallucinations in the Caribbean group, but non-migrants reported significantly higher rates of hallucinations in the South Asian group. A likely explanation for the low prevalence rate in South Asian migrants was the poorer understanding of the questions in this group. Although the research method was designed to overcome linguistic difficulties (the interviews were conducted by ethnically matched interviewers in the language of the respondent's choice), the ideas contained in the questions may have been unfamiliar to people from a different cultural or linguistic background, making the measures less reliable for those more distant from Western culture (Berthoud & Nazroo, 1997; Nazroo, 1997).
Hallucinations and mental health problems
These data are consistent with the view of a continuum of psychotic
phenomena in the general population. Of the respondents who answered
positively to the first hallucination item on the PSQ, less than half endorsed
the second question as well and half reported another item on the PSQ. Of
those who reported hallucinatory experiences, only a small percentage (about
11% in the White group) reported a diagnosis of psychosis or treatment for
psychosis. This percentage was lower in the Caribbean group (2%), showing an
increased discrepancy between the prevalence of PSQ hallucinatory experiences
and reported psychosis diagnosis in this sample. Of those respondents who
screened positive on the PSQ hallucination questions (i.e. those who endorsed
both questions and were followed up), 25% met the PSE criteria for a psychotic
disorder. This was consistent across ethnic groups. Interestingly, about half
of those who were positive on the PSQ hallucination criterion but who did not
meet the PSE criteria for a psychotic disorder met the criteria for a neurotic
disorder.
Ethnicity and psychosis
The variation in hallucinatory experiences according to ethnic group is
consistent with the main survey findings of ethnic differences, but the
results are not in agreement with other studies on ethnicity and psychosis.
The higher rate of hallucinations in the Caribbean group seems to be
consistent with reports of higher rates of schizophrenia and other psychoses
in AfricanCaribbean people
(Wesseley et al,
1991; van Os et al,
1996). However, Caribbean females reported more hallucinatory
experiences than males in this study, whereas increased psychosis rates have
been associated with both AfricanCaribbean males and females. The
Fourth National Survey of Ethnic Minorities did find a higher rate of
psychosis for Caribbean women, although this was not statistically significant
and there was no difference for men
(Nazroo, 1997).
The similar prevalence of hallucinations in Caribbean migrants and non-migrants corresponds with the findings of the Fourth National Survey of no difference in psychosis rates between these two groups (Nazroo, 1997), but the results are not consistent with reports of increased rates of psychosis in second-generation AfricanCaribbean immigrants (McGovern & Cope, 1987; Harrison et al, 1988). The contradiction between the Fourth National Survey findings on prevalence in the community and other studies of incidence leading to hospital admission is discussed in Nazroo (1997), Berthoud & Nazroo (1997) and Nazroo (1998). The relationship between ethnic variation in the experience of hallucinations and the presence of psychotic disorders is unclear. It has been argued that a lack of awareness of cultural differences in hallucinations and other psychotic phenomena can lead to patients from ethnic minority groups being misdiagnosed as suffering from schizophrenia (Shashidharan, 1993). On the other hand, studies have shown that elevated rates of psychosis in AfricanCaribbean people are not due to misdiagnosis (Lewis et al, 1990; Hickling et al, 1999). This survey suggests that, for all ethnic groups, self-reports of hallucinations are not invariably associated with mental health problems.
Continuum of hallucinations
Reports of hallucinatory experiences in the general population provide
additional evidence that psychosis is on a continuum with normality. Cognitive
psychological models have attempted to explain how anomalous experiences are
transformed into psychotic symptoms (Garety
et al, 2001). It is suggested that disruption of normal
cognitive processes leads to anomalous conscious experiences. These
experiences, often puzzling and associated with emotional changes, can seem
personally relevant and trigger a search for explanation as to their cause.
Biased conscious appraisal processes contribute to a judgement that these
confusing experiences (which may feel externally generated) are, in fact,
externally caused. Thus, a tendency to form abnormal beliefs may be a crucial
factor in generating psychotic hallucinations. It may be possible also that
delusional descriptions arise when there is no ready alternative explanation
and the hallucinatory experience does not fit into a shared cognitive or
cultural framework.
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Clinical Implications and Limitations |
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LIMITATIONS
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Received for publication December 14, 2000. Revision received June 8, 2001. Accepted for publication June 13, 2001.
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