| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
| Psychiatric Bulletin | Advances in Psychiatric Treatment | All RCPsych Journals |
|
|
|
||||||||||
|
||||||||||||
Academic Unit of Psychiatry, Department of Community Based Medicine, University of Bristol
Division of Psychological Medicine, Cardiff University
Department of Mental Health Sciences, Royal Free and University College Medical School, University College London
Drugs and Alcohol Research Programme, Research Development & Statistics Directorate, Home Office, London
Office for National Statistics, London
Academic Unit of Psychiatry, Department of Community Based Medicine, University of Bristol, UK
Correspondence: Dr Nicola J. Wiles, Academic Unit of Psychiatry, Department of Community Based Medicine, University of Bristol, The Grange, 1 Woodland Road, Bristol BS8 1AU, UK. Tel: +44 (0)117 954 6676; fax: +(0)117 331 0964; e-mail: nicola.wiles{at}bristol.ac.uk
Funding detailed in Acknowledgements.
 |
ABSTRACT |
|---|
 TOP ABSTRACT INTRODUCTIONMETHODRESULTSDISCUSSIONClinical Implications and...ACKNOWLEDGMENTSREFERENCES |
|---|
Aims To estimate the incidence of, and risk factors for, self-reported psychotic symptoms in Great Britain.
Method Data from the 18-month follow-up of a national survey were used. Incident cases were those who endorsed one or more items on the Psychosis Screening Questionnaire at follow-up, but not at baseline. The association between factors recorded at baseline and incident self-reported symptoms was examined.
Results At follow-up, 4.4% of the general population reported incident psychotic symptoms. Six factors were independently associated with incident symptoms: living in a rural area; having a small primary support group; more adverse life events; smoking tobacco; neurotic symptoms; and engaging in a harmful pattern of drinking.
Conclusions A small but not insignificant percentage of the population of Great Britain reported incident psychotic symptoms over 18 months. The risk factors for psychotic symptoms showed some similarities with risk factors for schizophrenia, but there were also some striking differences. The relationship between such risk factors and the factors that perpetuate psychotic symptoms remains to be ascertained.
|
|
INTRODUCTION |
|---|
|
TOPABSTRACTINTRODUCTIONMETHODRESULTSDISCUSSIONClinical Implications and...ACKNOWLEDGMENTSREFERENCES |
|---|
The 18-month follow-up of participants in the British National Survey of Psychiatric Morbidity provides a rare opportunity to examine the incidence of, and risk factors for, self-reported psychotic symptoms using prospective longitudinal data.
|
|
METHOD |
|---|
|
TOPABSTRACTINTRODUCTIONMETHODRESULTSDISCUSSIONClinical Implications and...ACKNOWLEDGMENTSREFERENCES |
|---|
12) at the time
of the cross-sectional survey and those with sub-threshold neurotic symptoms
(CIS–R score 6–11) were eligible for follow-up, as were a random
20% of those without a mental disorder. Using the above criteria, 3536 persons
were selected for follow-up, the majority of whom (n=3045) were
successfully contacted. More than three-quarters (79%, n=2413)
completed the follow-up interview, 17% (n=503) refused, and contact
was not made with 129 (4%). The Multicentre Research Ethics Committees in
England granted ethical approval for the study.
Measurement of psychotic symptoms
Positive psychotic symptoms comprise anomalous experiences (hallucinations,
thought insertion) and abnormal beliefs (delusions). Classically, these are
identified by a process of cross-examination, whereby the definition of the
symptoms is matched with someone’s experience
(Brugha et al, 1999),
but in-depth psychiatric interviews are impractical for large population
surveys. Lay interviews are a less rigorous method of establishing psychotic
symptoms, but there is evidence that people who endorse items on the Psychosis
Screening Questionnaire (PSQ; Bebbington
& Nayani, 1995) are similar to those who are actually
diagnosed using a standardised clinical instrument
(Johns et al, 2002),
suggesting that there are continuities.
In our study the presence of psychotic symptoms was elicited (at baseline and follow-up) using the PSQ, which includes five sections relating to hypomania, thought insertion, paranoia, strange experiences and hallucinations. Each section begins with an introductory question, which, if the participant answers positively, is followed by one or two key questions. A positive response to a key question would normally mean that subsequent sections of the questionnaire are omitted, as those individuals would be regarded as ‘screen positive’ and would undergo a clinical assessment to establish the presence (or absence) of psychosis. However, for the purposes of the ONS survey, each of the five introductory PSQ questions was asked (with key questions). In the initial survey, the reference period for reporting symptoms was the 12 months prior to interview. For the follow-up survey, this was amended to the entire period since the previous interview (approximately 18 months).
Baseline assessment of psychosis
A two-stage process (Meltzer et
al, 1994; Singleton
et al, 1998) was used to exclude individuals with a
psychotic disorder at baseline from the data-set. Participants were regarded
as screening positive for a psychotic disorder if they self-reported a
diagnosis or had symptoms suggestive of a psychotic disorder (e.g.
hallucinations), were in receipt of antipsychotic medication, had been
previously admitted to a psychiatric hospital or had responded positively to
the question about auditory hallucinations on the PSQ. These individuals, and
a sample of those who were screen negative, were selected for clinical
interview. Diagnoses of psychotic disorder according to ICD–10 criteria
(World Health Organization,
1993) were obtained using the computerised version 2.1 of the
Schedules for Clinical Assessment in Neuropsychiatry (SCAN;
Wing et al, 1990).
People who refused to take part in the second interview or could not be
contacted were assigned a diagnosis of probable psychotic disorder if they met
at least two of the four psychosis screening criteria
(Singleton et al,
1998).
Statistical analysis
All analyses were conducted in Stata version 8 for Windows using the svy
commands. Probability weights were used to account for the stratified sampling
procedure and non-response. Full details of the weighting procedure are
provided in the ONS report (Singleton
& Lewis, 2003).
Occurrence of self-reported psychotic symptoms
The prevalence of psychotic symptoms at baseline was estimated, together
with the persistence of such symptoms.
Incident self-reported psychotic symptoms and risk factor identification
The emergence of incident psychotic symptoms (thought insertion, paranoia,
strange experiences and hallucinations) between the baseline and follow-up
surveys, at the level of the introductory and key questions, was ascertained
for the entire cohort and stratified by gender. The term ‘incident
symptoms’ was used to describe ‘new onset’ symptoms that
occurred between baseline and follow-up. It is possible that such symptoms
will not represent their first-ever occurrence, but a true measure of incident
psychotic symptoms is difficult to obtain in adults. We assume that these
errors will primarily lead to random misclassification.
Subsequent analyses examined risk factors for incident psychotic symptoms
at follow-up. A positive response to the first key question for any of the
four sections covering thought insertion, paranoia, strange experiences and
hallucinations was defined as an incident psychotic symptom. Based on the
epidemiology of schizophrenia, the following variables, recorded at baseline,
were examined for their association with self-reported psychotic symptoms at
follow-up: age; gender; baseline CIS–R score; marital status (married,
cohabiting, single, widowed, divorced or separated); area type (interviewer
rating of urban, semi-rural or rural); IQ score, measured using the National
Adult Reading Test (Nelson,
1982); size of primary support group, a measure of the
individual’s social network based on the number of close friends and
relatives: 0–3, 4–8 or 9 (Brugha et al,
1987,
1993); number of life events,
using a list of 18 items (Singleton et
al, 1998) covering issues such as relationship difficulties,
bereavement, illness, employment and financial problems (0–1, 2, 3, 4, 5
or 6); current smoking status; alcohol use, measured using the Alcohol Use
Disorders Identification Test score 0–40 (AUDIT;
Saunders et al,
1993); and cannabis use (not used in past year, used in past year
but no report of dependency, dependent on cannabis). Dependency on cannabis
was based on a positive response to one of five questions (daily use for 2 or
more weeks, self-reported dependence, inability to cut down, need to use
larger quantities to get an effect, or symptoms of withdrawal).
In addition, a number of socioeconomic indicators were examined: highest
educational qualification (degree; teaching, Higher National Diploma or
nursing qualification; A-level; General Certificate of Secondary Education or
equivalent; or no qualifications), employment status (working full-time;
working part-time; unemployed; long-term sick or disabled; other economically
inactive), social class (I–V), using the 1991 Registrar General’s
Standard Occupational Classification
(Office for Population Censuses and
Surveys, 1991), accommodation tenure (owned outright; owned with
mortgage; rented from local authority or housing association; or rented from
other source) and weekly gross income (<£100, £100–199,
£200–299, £300–399 or £400).
Logistic regression was used to examine the association between baseline
variables and the onset of psychotic symptoms at follow-up. Univariable
associations (in terms of odds ratios) and their 95% confidence intervals are
reported. Given the rarity of the outcome, these may be interpreted as rate
ratios (Rothman & Greenland,
1998). All variables significant at P
0.20 in the
univariable model were entered into a multivariable model to permit
identification of independent associations. Age, gender, baseline CIS–R
score and use of psychotropic drugs or receipt of therapy were included in the
model, which was simplified using the likelihood ratio test
(Hosmer & Lemeshow, 1989).
All variables significant at P<0.10 were retained. Previously
excluded variables (univariable, P>0.20) were added to the
multivariable model to determine whether they contributed significantly; any
that became significant at P<0.10 were retained.
Data-set
In total, 2406 participants completed the baseline and follow-up surveys.
Of these, 3 individuals with missing data on psychotic symptoms and 24
individuals with psychotic disorder at baseline (SCAN or
‘probable’ diagnoses) were excluded from all analyses. People who
reported psychotic symptoms at baseline (thought insertion, paranoia, strange
experiences or hallucinations; n=414) were excluded from analyses
examining the risk factors for incident symptoms. Of the remaining 1965
persons, 1795 (91%) had data available on the specified predictors.
|
|
RESULTS |
|---|
|
TOPABSTRACTINTRODUCTIONMETHODRESULTSDISCUSSIONClinical Implications and...ACKNOWLEDGMENTSREFERENCES |
|---|
|
Incident self-reported psychotic symptoms
Of the 1965 participants without psychotic symptoms at baseline, 134
(weighted estimate 4.4%, 95% CI 3.3–5.6) reported incident symptoms at
follow-up (Table 2). Only 17
individuals endorsed two or more psychotic symptoms at follow-up. More people
endorsed the introductory questions of the PSQ
(Table 2). Paranoid thoughts
were the most commonly reported symptom (weighted estimate 3.3%). Incident
psychotic symptoms were more frequent in men (5.1%) than in women (3.8%),
although this was not true of positive responses to the introductory question
(Table 2).
|
Risk factors for self-reported incident psychotic symptoms
Baseline CIS–R score was strongly associated with incident
self-reported psychotic symptoms (Table
3). The risk of incident psychotic symptoms was double for
inhabitants of rural areas and for current tobacco smokers
(Table 3). A small primary
support group and a greater exposure to life events were both strongly
associated with incident psychotic symptoms on univariable analysis.
Individuals engaging in harmful drinking (AUDIT score 16) also had an
increased risk of incident psychotic symptoms at follow-up, as did those
dependent on cannabis. There was little evidence for an association with
marital status, low IQ score, educational qualifications, employment status,
gross weekly income, social class or housing tenure.
|
On multivariable analyses, six factors were identified as being independently associated with incident self-reported psychotic symptoms (Table 4). Those living in rural areas had a three-fold risk of reporting de novo psychotic symptoms at follow-up, as did those with a small primary support group (size <4). The number of life events recorded at baseline remained strongly associated with an increased risk of incident psychotic symptoms. Individuals who smoked tobacco or engaged in a harmful pattern of drinking had a doubled risk of psychotic symptoms at follow-up. In addition, baseline CIS–R score was strongly associated with incident psychotic symptoms. Women and older individuals were less likely to experience incident symptoms, but this was not statistically significant (P=0.21 and Plinear trend=0.16 respectively).
|
After further adjustment for use of cannabis, IQ score and marital status at baseline most of these associations persisted (Table 4), although the confidence intervals surrounding the effect estimates for current smoking and harmful drinking now included unity. Those dependent on cannabis had a slightly increased risk of reporting incident psychotic symptoms, although the confidence interval was wide. The associations between IQ score and marital status and incident self-reported psychotic symptoms were weak (Table 4). Using a more stringent definition to define psychotic symptoms (positive response to at least one of the highest key questions) did not alter the conclusions (data not shown).
|
|
DISCUSSION |
|---|
|
TOPABSTRACTINTRODUCTIONMETHODRESULTSDISCUSSIONClinical Implications and...ACKNOWLEDGMENTSREFERENCES |
|---|
Comparison with the results of previous studies
In cross-sectional analyses, women, younger individuals, residents of urban
areas, those who had never married, those with lower levels of income or lower
IQ, the less educated, the unemployed, those dependent on drugs or alcohol,
those who had experienced more adverse life events and those with neurotic
symptoms were more likely to report psychotic symptoms
(van Os et al, 2000;
Olfson et al, 2002;
Johns et al, 2004).
It is difficult to disentangle the temporal nature of such cross-sectional
associations. Some findings may be due to reverse causality, whereas other
factors may be associated with chronicity rather than symptom onset. Cannabis
use is the only factor to have consistently been linked with psychotic
symptoms in previous longitudinal studies (Arseneault et al, 2002;
van Os et al, 2002;
Fergusson et al,
2003). Little else is known about the aetiology of psychotic
symptoms.
In common with earlier cross-sectional findings from the British National Psychiatric Morbidity Survey (Johns et al, 2004), we observed an association between the number of adverse life events, psychiatric morbidity (CIS–R score), alcohol dependency and self-reported psychotic symptoms. We were unable to explore the previously reported variation by ethnic group (Johns et al, 2002; King et al, 2005) given the small number of participants from Black and minority ethnic groups.
Participants dependent on cannabis at baseline were at a slightly increased risk of reporting psychotic symptoms at follow-up. Although a precise effect could not be determined owing to the small numbers, our findings are in line with the results of previous population-based longitudinal studies that have linked cannabis use with the onset of psychosis (Arseneault et al, 2002; van Os et al, 2002; Zammit et al, 2002; Fergusson et al, 2003) and provided evidence for a dose–response effect (van Os et al, 2002; Zammit et al, 2002).
A link between urbanicity and psychotic symptoms has been shown in many studies (including van Os et al, 2000, 2001; Sundquist et al, 2004). However, we found that individuals living in rural areas were at increased risk of incident psychotic symptoms. Our measure of urbanicity was based on the interviewer’s rating of the area (urban, semi-rural or rural), avoiding the potential for misclassification that may occur when measures of population density are used in areas of substantial heterogeneity. Previous cross-sectional analyses of the British National Psychiatric Morbidity Survey found that urban residence was, in univariable analysis, weakly associated with self-reported psychotic symptoms but was not significantly associated on multivariable analysis (Johns et al, 2004). We acknowledge that the direction of this association was unexpected and requires further investigation. Indeed, there may be ‘critical periods’ during which exposure to particular factors (such as area of residence) may be most relevant. Thus differences in the timing of exposure (e.g. current place of residence rather than place of upbringing or birth) may account for the discrepancy. In order to formally test the hypothesis that different risk factors operate at different times we would need to examine the interaction between age and individual risk factors, but in the context of such a rare outcome it is not appropriate to conduct such tests as they would be severely underpowered (and hence the likelihood of a type II error is high).
The role of smoking also remains unclear. Over 80% of individuals with schizophrenia claim to have started smoking before the onset of their disease (Beratis et al, 2001). A positive association between smoking and schizophrenia has been found in crude analysis (Zammit et al, 2003; Weiser et al, 2004), but after adjustment for confounders, smokers had a reduced risk of developing schizophrenia in one study (Zammit et al, 2003), and an increased risk in the other (Weiser et al, 2004). This may reflect differences in the duration of follow-up or more limited adjustment for confounders in the latter study. In our study, smokers had a 70% greater risk of incident psychotic symptoms. This may be causal or may reflect self-medication by those in the prodrome, but it was not possible to stratify on time to occurrence of psychotic symptoms (Zammit et al, 2003) to exclude the latter possibility.
The finding that a small primary support group (few close friends or relatives) was associated with a greater likelihood of reporting incident psychotic symptoms was interesting. It is plausible that social isolation might contribute to the development of negative schemas in these individuals and thus play a part in the development of psychotic symptoms (Garety et al, 2001).
Our analysis provided little evidence that marital status, educational qualifications, employment status or income were risk factors for incident psychotic symptoms. Although such factors are important in the aetiology of psychotic disorder, there is an absence of longitudinal data on the role of such factors in the aetiology of psychotic symptoms. The results of our study suggest that there may be some continuity in the risk factors for psychosis and self-reported psychotic symptoms, but – importantly – there may be differences.
There was a strong association between baseline CIS–R score (neurotic symptoms) and incident psychotic symptoms. This concurs with the literature on schizophrenia where, in Swedish conscripts, neurosis has been linked with later schizophrenia, with the evidence suggesting that this may be a prodromal phase of the disease (Lewis et al, 2000). In contrast, although longitudinal population studies have linked low IQ score with psychotic disorder (David et al, 1997; Zammit et al, 2004), the association between IQ score and incident psychotic symptoms within this study was inconclusive. A 10-point increase in IQ score was associated with a 12% decrease (OR=0.88) in the risk of incident psychotic symptoms, but the confidence limits were wide.
Strengths and limitations of the study
This nationally representative population sample has permitted us to
examine the incidence of self-reported psychotic symptoms. Furthermore, the
longitudinal design permitted us to examine a number of potential aetiological
risk factors and – given the exclusion of those with prevalent symptoms
at baseline from the denominator – to (tentatively) suggest causality.
In cross-sectional studies it has not been possible to disentangle risk
factors for symptom onset from those for chronicity. However, the possibility
that some factors (e.g. adverse life events and alcohol or drug use) may
reflect premorbid personality cannot be ruled out. Only a longitudinal study
with multiple repeated measures of psychotic symptoms and risk factors over
many years from adolescence into adulthood could help exclude such a
possibility. To date, no such work has been conducted.
There are a number of limitations. The PSQ was designed as a screening tool for psychotic disorder. The use of lay interviewers broadens the definition and lowers the threshold for recognition, and thus increases prevalence above that ascertained by clinical interview. However, individuals endorsing items on the PSQ are similar to those identified as having psychosis by clinical interview (Bebbington & Nayani, 1995), suggesting that people with psychosis may emerge from the pool of those with minor psychotic-like experiences and beliefs. It has been suggested that the major difference is the level of preoccupation, distress and disability in those with psychotic illness. Endorsement of key questions in the PSQ probably identified psychotic-like experiences and beliefs in some people who are relatively untroubled by them, but also in some who are on the edge of diagnosable psychosis. We cannot exclude the possibility that, in some individuals, the psychotic symptoms might have occurred during periods of intoxication (illicit drugs or alcohol) and that others might have reported hallucinations occurring during physical illness.
Finally, given the low incidence of psychotic symptoms, the study may be underpowered to detect associations, particularly with rare exposures. This is reflected in the wide confidence intervals surrounding a number of the effect estimates. For this reason we are not able to examine risk factors for persistent psychotic symptoms in this data-set.
Future research
The epidemiology of psychotic symptoms has some similarities with the
epidemiology of schizophrenia, but there are also some striking differences.
Further understanding of these differences might help to explain the
relationship between early stages of psychosis and disabling psychotic
illnesses.
|
|
Clinical Implications and Limitations |
|---|
|
TOPABSTRACTINTRODUCTIONMETHODRESULTSDISCUSSIONClinical Implications and...ACKNOWLEDGMENTSREFERENCES |
|---|
LIMITATIONS
|
|
ACKNOWLEDGMENTS |
|---|
|
TOPABSTRACTINTRODUCTIONMETHODRESULTSDISCUSSIONClinical Implications and...ACKNOWLEDGMENTSREFERENCES |
|---|
|
|
REFERENCES |
|---|
|
TOPABSTRACTINTRODUCTIONMETHODRESULTSDISCUSSIONClinical Implications and...ACKNOWLEDGMENTSREFERENCES |
|---|
Bebbington, P. & Nayani, T. (1995) The psychosis screening questionnaire. International Journal of Methods in Psychiatric Research, 5, 11 –19.[Medline]
Beratis, S., Katrivanou, A. & Gourzis, P. (2001) Factors affecting smoking in schizophrenia. Comprehensive Psychiatry, 42, 393 –402.[CrossRef][Medline]
Brugha, T. S., Sturt, E., MacCarthy, B., et al (1987) The Interview Measure of Social Relationships: the description and evaluation of a survey instrument for assessing personal social resources. Social Psychiatry, 22, 123 –128.[Medline]
Brugha, T. S., Wing, J. K., Brewin, C. R., et al (1993) The relationship of social network deficits with deficits in social functioning in long-term psychiatric disorders. Social Psychiatry and Psychiatric Epidemiology, 28, 218 –224.[Medline]
Brugha, T. S., Bebbington, P. E. & Jenkins, R. (1999) A difference that matters: comparisons of structured and semi-structured psychiatric diagnostic interviews in the general population. Psychological Medicine, 29, 1013 –1020.[CrossRef][Medline]
David, A. S., Malmberg, A., Brandt, L., et al (1997) IQ and risk for schizophrenia: a population-based cohort study. Psychological Medicine, 27, 1311 –1323.[CrossRef][Medline]
Eaton, W. W., Romanoski, A., Anthony, J. C., et al (1991) Screening for psychosis in the general population with a self-report interview. Journal of Nervous and Mental Disease, 179, 689 –693.[Medline]
Fergusson, D. M., Horwood, L. J. & Swain-Campbell, N. R. (2003) Cannabis dependence and psychotic symptoms in young people. Psychological Medicine, 33, 15 –21.[CrossRef][Medline]
Garety, P. A., Kuipers, E., Fowler, D., et al (2001) A cognitive model of the positive symptoms of psychosis. Psychological Medicine, 31, 189 –195.[CrossRef][Medline]
Hosmer, D. W. J. & Lemeshow, S. (1989) Applied Logistic Regression. New York: Wiley.
Janssen, I., Hanssen, M., Bak, M., et al
(2003) Discrimination and delusional ideation.
British Journal of Psychiatry,
182, 71
–76.
Johns, L. C., Nazroo, J. Y., Bebbington, P., et al
(2002) Occurrence of hallucinatory experiences in a community
sample and ethnic variations. British Journal of
Psychiatry, 180, 174
–178.
Johns, L. C., Cannon, M., Singleton, N., et al
(2004) Prevalence and correlates of self-reported psychotic
symptoms in the British population. British Journal of
Psychiatry, 185, 298
–305.
King, M., Nazroo, J. Y., Weich, S., et al (2005) Psychotic symptoms in the general population of England. A comparison of ethnic groups (the EMPIRIC study). Social Psychiatry and Psychiatric Epidemiology, 40, 375 –381.[CrossRef][Medline]
Lewis, G. (1994) Assessing psychiatric disorder with a human interviewer or a computer. Journal of Epidemiology and Community Health, 48, 207 –210.[Abstract]
Lewis, G., Pelosi, A. J., Araya, R., et al (1992) Measuring psychiatric disorder in the community: a standardized assessment for use by lay interviewers. Psychological Medicine, 22, 465 –486.[Medline]
Lewis, G., David, A. S., Malmberg, A., et al
(2000) Non-psychotic psychiatric disorder and subsequent risk
of schizophrenia: cohort study. British Journal of
Psychiatry, 177, 416
–420.
Meltzer, H., Gill, B., Petticrew, M., et al (1994) OPCS Surveys of Psychiatric Morbidity in Great Britain, Report 1: The Prevalence of Psychiatric Morbidity Among Adults Living in Private Households. London: HMSO.
Nelson, H. E. (1982) National Adult Reading Test. Windsor: NFER–Nelson.
Office for Population Censuses and Surveys (1991) Standard Occupational Classification. London: HMSO.
Olfson, M., Lewis-Fernandez, R., Weissman, M. M., et al
(2002) Psychotic symptoms in an urban general medicine
practice. American Journal of Psychiatry,
159, 1412
–1419.
Rothman, K. J. & Greenland, S. (1998) Modern Epidemiology. Philadelphia, PA: Lippincott-Raven.
Saunders, J. B., Aasland, O. G., Babor, T. F., et al (1993) Development of the Alcohol Use Disorders Identification Test (AUDIT); WHO collaborative project on early detection of persons with harmful alcohol consumption – II. Addiction, 88, 791 –804.[CrossRef][Medline]
Singleton, N. & Lewis, G. (2003) Better or Worse: A Longitudinal Study of the Mental Health of Adults Living in Private Households in Great Britain. London:TSO (The Stationery Office).
Singleton, N., Meltzer, H., Gatward, R., et al (1998) Psychiatric Morbidity Among Prisoners in England and Wales. London: TSO (The Stationery Office).
Singleton, N., Bumpstead, R., O’Brien, M., et al (2001) Psychiatric Morbidity Among Adults Living in Private Households, 2000. London:TSO (The Stationery Office).
Sundquist, K., Frank, G. & Sundquist, J.
(2004) Urbanisation and incidence of psychosis and
depression: follow-up study of 4.4 million women and men in Sweden.
British Journal of Psychiatry
184, 293
–298.
Tien, A. Y. (1991) Distributions of hallucinations in the population. Social Psychiatry and Psychiatric Epidemiology, 26, 287 –292.[CrossRef][Medline]
Van Os, J. & Verdoux, H. (2002) Diagnosis and classification of schizophrenia: categories versus dimensions, distributions versus disease. In The Epidemiology of Schizophrenia (eds R. Murray, P. B. Jones, E. Susser, et al), pp. 364–410. Cambridge: Cambridge University Press.
Van Os, J., Hanssen, M., Bijl, R. V., et al (2000) Strauss (1969) revisited: a psychosis continuum in the general population? Schizophrenia Research, 45, 11 –20.[CrossRef][Medline]
Van Os, J., Hanssen, M., Bijl, R. V., et al
(2001) Prevalence of psychotic disorder and community level
of psychotic symptoms: an urban–rural comparison. Archives of
General Psychiatry, 58, 663
–668.
Van Os, J., Bak, M., Hanssen, M., et al
(2002) Cannabis use and psychosis: a longitudinal
population-based study. American Journal of
Epidemiology, 156, 319
–327.
Verdoux, H., van Os, J., Maurice-Tison, S., et al (1998) Is early adulthood a critical developmental stage for psychosis proneness? A survey of delusional ideation in normal subjects. Schizophrenia Research, 29, 247 –254.[CrossRef][Medline]
Weiser, M., Reichenberg, A., Grotto, I., et al
(2004) Higher rates of cigarette smoking in male adolescents
before the onset of schizophrenia: a historical prospective cohort study.
American Journal of Psychiatry,
161, 1219
–1223.
Wing, J. K., Babor, T., Brugha, T., et al (1990) SCAN. Schedules for Clinical Assessment in Neuropsychiatry. Archives of General Psychiatry, 47, 589 –593.[Abstract]
World Health Organization (1993) The ICD–10 Classification of Mental and Behavioural Disorders. Diagnostic Criteria for Research. Geneva: WHO.
Zammit, S., Allebeck, P., Andreasson, S., et al
(2002) Self reported cannabis use as a risk factor for
schizophrenia in Swedish conscripts of 1969: historical cohort study.
BMJ, 325, 1199
–1202.
Zammit, S., Allebeck, P., Dalman, C., et al
(2003) Investigating the association between cigarette
smoking and schizophrenia in a cohort study. American Journal of
Psychiatry, 160, 2216
–2221.
Zammit, S., Allebeck, P., David, A. S., et al
(2004) A longitudinal study of premorbid IQ score and risk of
developing schizophrenia, bipolar disorder, severe depression, and other
nonaffective psychoses. Archives of General
Psychiatry, 61, 354
–360.
Received for publication April 13, 2005. Revision received September 29, 2005. Accepted for publication October 27, 2005.
Related articles in BJP:
This article has been cited by other articles:
|
|
 |
|
  J. Horwood, G. Salvi, K. Thomas, L. Duffy, D. Gunnell, C. Hollis, G. Lewis, P. Menezes, A. Thompson, D. Wolke, et al. IQ and non-clinical psychotic symptoms in 12-year-olds: results from the ALSPAC birth cohort The British Journal of Psychiatry, September 1, 2008; 193(3): 185 - 191. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 L. A. Nicholson Rural mental health Advan. Psychiatr. Treat., July 1, 2008; 14(4): 302 - 311. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 D. Collip, I. Myin-Germeys, and J. Van Os Does the Concept of "Sensitization" Provide a Plausible Mechanism for the Putative Link Between the Environment and Schizophrenia? Schizophr Bull, March 1, 2008; 34(2): 220 - 225. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
J. Macleod Cannabis use and psychosis: the origins and implications of an association Advan. Psychiatr. Treat., November 1, 2007; 13(6): 400 - 411. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
J. Allardyce, W. Gaebel, J. Zielasek, and J. van Os Deconstructing Psychosis Conference February 2006: The Validity of Schizophrenia and Alternative Approaches to the Classification of Psychosis Schizophr Bull, July 1, 2007; 33(4): 863 - 867. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
R. Dutta, T. Greene, J. Addington, K. McKenzie, M. Phillips, and R. M. Murray Biological, Life Course, and Cross-Cultural Studies All point Toward the Value of Dimensional and Developmental Ratings in the Classification of Psychosis Schizophr Bull, July 1, 2007; 33(4): 868 - 876. [Abstract] [Full Text] [PDF]
|
|
Read all eLetters
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
| Psychiatric Bulletin | Advances in Psychiatric Treatment | All RCPsych Journals |
