Institute of Psychiatry, London, UK
European Graduate School of Neuroscience, Maastricht University, The Netherlands, and Institute of Psychiatry, London, UK
Institute of Psychiatry, London, UK
University of Western Australia, Perth, Australia
Crichton Royal Hospital, Dumfries, UK
Institute of Psychiatry, London, UK
Correspondence: Dr. J. Boydell, Division of Psychological Medicine, Institute of Psychiatry, De Crespigny Park, Denmark Hill, London SE5 8AF, UK. Tel: 020 7848 0260; e-mail: j.boydell{at}iop.kcl.ac.uk
Funding detailed in Acknowledgements.
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ABSTRACT |
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Aims To identify any changes in incidence of schizophrenia in Camberwell, south-east London, between 1965 and 1997.
Method Research Diagnostic Criteria and DSMIIIR diagnoses were generated for all first contacts by the OPCRIT computer program, and incidence rates of schizophrenia in seven time periods were measured. Indirect standardisation and Poisson models were used to measure the effect of time period and to examine interactions with age and gender.
Results There was a continuous and statistically significant increase in the incidence of schizophrenia, which was greatest in people under 35 years of age and was not gender-specific.
Conclusions The incidence of schizophrenia has doubled in south-east London over the past three decades.
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INTRODUCTION |
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METHOD |
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Sample
We collected clinical and demographic data on all people from the
geographically defined area of Camberwell in south-east London, who presented
with psychosis between 1965 and 1997. This 33-year period was broken down into
two 4-year and five 5-year periods (1965-1968=1, 1969-1972=2, 1973-1977=3,
1978-1982=4, 1983-1987=5, 1988-1992=6, 1993-1997=7). Cases were initially
identified using the Camberwell Case Register
(Wing & Hailey, 1972) and
then psychiatric hospital computer records (from 1984), by generating a list
of all people admitted to any hospital serving the Camberwell catchment area,
with any possible psychotic illness (ICD-9 codes 295, 295.6, 297, 296.0,
296.2, 296.4, 298, 292.1 (World Health
Organization, 1978) and ICD10 codes F20, F25, F22, F30,
F31.3, F31.2, F31.6, F28, F29, F12.5, F16.6, F19.5, F16.75, F19.75
(World Health Organization,
1992)). In addition, all case records of all patients from the
area were examined to identify those who made contact with services but were
not admitted. The records of those not admitted were of a similar standard to
the records of those admitted. Patients who were admitted to hospitals outside
the area would usually be transferred back to local hospitals or referred to
local services for continuing care. These records were also identified in the
comprehensive search of all case notes. The methodology and the
characteristics of the area are more fully described by Castle et al
(1998) and Allardyce et
al (2001).
Diagnostic procedure
Patients' records were then checked to ensure that they were true incident
cases (i.e. had not had previous psychiatric treatment for a psychotic or
possible psychotic illness), and then were rated using the Operational
Criteria (OPCRIT) checklist. All cases presenting between 1992 and 1997 were
rated by J.B., who monitored interrater reliability for RDC schizophrenia by
independently rating a random sample of case records that were already on the
database. Reliability was found to be good (kappa=0.79 for RDC schizophrenia).
Previous interrater reliability exercises have been detailed by Castle et
al (1991,
1998) and van Os et al
(1996). The OPCRIT checklist
is based on phenomenological descriptions in the Present State Examination
(Wing et al, 1974)
and enables computer diagnoses to be made using the OPCRIT program
(McGuffin et al,
1991). The OPCRIT checklists were then used to generate RDC
(Spitzer et al, 1978)
diagnoses using the computer program. RDC schizophrenia was chosen for this
analysis because the criteria have been incorporated in the OPCRIT system
since it was devised, and because of a preference for using a broad definition
of schizophrenia for research. (The earlier OPCRIT were rated before
ICD10 and DSMIV (American
Psychiatric Association, 1994) criteria were available.)
OPCRIT-derived DSMIIIR diagnoses were also analysed to check the
results, as this is a narrower definition of schizophrenia
(Table 1).
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Denominator data
Population data were estimated using the 10-year censuses (data from the
Office of Population Censuses and Surveys, Population Estimates Unit, 1997)
and London Research Centre
(1997) projections for 1997,
which include corrections for under-numeration. Corrections were applied as
appropriate throughout the time period.
Statistical analyses
A correction was made for notes known to be missing (as a percentage of
total subjects in each time period). More notes were definitely missing from
the case register, which made the analysis more conservative. Raw and
corrected figures are shown in Table
2. All further analyses and results pertain to the corrected
figures.
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Indirect standardisation was carried out using rates for the total population, stratifying for age and gender, as the standard and applying them to each time period, using the ISTDIZE procedure in the STATA statistical program (StataCorp, 1999). This allowed the number of expected cases in each time period to be determined. By dividing the actual observed cases by the expected cases, the standardised incidence ratio (SIR) was calculated. Incidence of schizophrenia was also modelled with Poisson regression analysis (StataCorp, 1999), which allowed for examination of interactions between age and gender on the one hand and time period on the other.
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RESULTS |
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The crude and adjusted incidence and SIRs, which are shown in Tables 3 and 4, indicate that the incidence of schizophrenia approximately doubled over the period of investigation.
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Poisson regression analysis, using schizophrenia as the dependent variable and time period as the independent variable, revealed a highly significant increase in the rate ratio over the seven time periods. The rate ratio linear trend (IRR) for RDC schizophrenia was 1.13 (95% CI 1.08-1.17; P<0.001), and adjusting for age (10-year age groups) and gender had little effect (IRR=1.12; 95% CI 1.08-1.16; P<0.001). For DSMIIIR, the IRR was 1.14 (95% CI 1.08-1.2; P<0.001) and 1.13 (95% CI 1.08-1.19; P<0.001) after adjusting for age and gender. This means that there was a statistically significant overall increase for both RDC and DSMIIIR schizophrenia.
There was a significant negative interaction between age and time period (IRR=0.96, P=0.007, RDC schizophrenia), meaning that the age of onset decreased as time period increased. To clarify this further, subjects were a priori classified as under 35 years of age or 35 years and older at the time of presentation. Table 5 shows that the increase with time was more significant in the younger age group. There was also a highly significant interaction between age and gender because, as expected, age at onset is later for women (IRR=1.44, P<0.001, RDC schizophrenia). However, there was no three-way interaction between age, gender and time period (IRR=0.996, P=0.71, RDC schizophrenia), indicating that the increase has been greatest in young people, not just young men. The results for DSMIIIR concurred.
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DISCUSSION |
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Methodological weaknesses
Findings
We demonstrated a large increase in the incidence of schizophrenia (whether
broadly or narrowly defined) in south-east London between 1965 and 1997. The
increase occurred particularly in young people and was not gender-specific.
The total numbers of all cases with any psychosis also increased with each
time period.
Interpretation
We have not reported the breakdown of the non-schizophrenia psychosis
cases, because OPCRIT is poor at producing RDC diagnoses for these cases (as
discussed above) and the change in version means that DSM and ICD would not be
reliable. This does not apply to the schizophrenia diagnoses. The total number
of psychosis cases increased over time and the proportion of schizophrenia
cases remained stable, so diagnostic shift cannot be an explanation for our
findings.
Our results were not adjusted for ethnicity because the population data before the 1981 census were based on approximate head-of-household figures unadjusted for age and gender (Castle et al, 1991), whereas later figures are considerably more accurate (van Os et al, 1996). We cannot therefore definitively address the question of whether migration into Camberwell may have contributed to the increase in incidence; nor can any conclusions be drawn from our study regarding aetiology of schizophrenia. This does not alter the implications of our findings for service provision and the need for greater resources.
Comparison with other studies
Comparison with other longitudinal studies is complex, because different
methodologies and different definitions of schizophrenia have been used
(Jablensky, 1997). Most
studies have shown a decline in incidence
(Geddes et al, 1993;
Munk-Jorgensen, 1995). However, many examined only admissions, at a time when a smaller proportion of
psychiatric patients was being admitted to hospital, when routine case
registers may not have been accurate and when clinical diagnoses were
susceptible to change over time.
Some studies have shown little or no change. Oldehinkel & Giel (1995), for example, found little change in all first psychiatric contacts between 1976 and 1990, for broadly defined schizophrenia in The Netherlands. Folnegovic et al (1990) found that admission rates did not change between 1965 and 1984. In Nottingham (UK), where the diagnoses were made by consensus, there has been an increase in psychosis as a whole but a decrease in narrowly defined schizophrenia (Brewin et al, 1997).
Two studies used methodology similar to that used in our study. The first was conducted in parallel with this study, in rural south-west Scotland between 1979 and 1998. It showed that an apparent decline in the administrative incidence of schizophrenia was in fact due to a narrowing of the concept of schizophrenia that local clinicians were using (Allardyce et al, 2000). There was no change in consistent OPCRIT-derived ICD and DSM schizophrenia diagnoses. The second study, in south Verona in Italy, found a decrease in ICD-10 paranoid and undifferentiated schizophrenia, but only in males, between 1975 and 1995 (Balestrieri et al, 1997).
Some studies have examined period effects (changes in how many people present at a particular time) and cohort effects (how many people present from successive birth cohorts), in an attempt to disentangle the influence of service and diagnostic factors and early aetiological factors (Takei et al, 1996; Suvisaari et al, 1999). We were not able to repeat this because we did not have comprehensive birth cohort and follow-up data for the area.
Further research
Further research might investigate the role of migration, social change
(especially decreasing social cohesion) and drug misuse in contributing to the
increased incidence of schizophrenia.
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Clinical Implications and Limitations |
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LIMITATIONS
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ACKNOWLEDGMENTS |
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We are greateful to the Stanley Foundation and the Gordon Small Trust for financial support.
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Received for publication May 21, 2001. Revision received August 12, 2002. Accepted for publication September 4, 2002.
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