Division of Psychiatry, University of Nottingham
Institute of Psychiatry, London
University of Cambridge, Addenbrooke's Hospital, Cambridge
Institute of Psychiatry, London
Department of Mental Health, University of Bristol
Institute of Psychiatry, London
University of Cambridge, Addenbrooke's Hospital, Cambridge, UK
ÆSOP study team
Correspondence: Dr Tuhina Lloyd, Division of Psychiatry, Duncan Macmillan House, Porchester Road, Nottingham NG3 6AA, UK. Tel: (0115) 9691300 x 30123; fax: (0115) 9555352; e-mail: Tuhina.Lloyd{at}nottingham.ac.uk
Declaration of interest None. Funding detailed in Acknowledgements.
![]() |
ABSTRACT |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
Aims To determine the incidence of operationally defined bipolar disorder in three areas of the UK and to investigate any differences in gender and ethnicity.
Method All patients who contacted mental health services with first-episode psychosis or non-psychotic mania between September 1997 and August 1999 were identified and diagnosed according to ICD-10 criteria. Incidence rates of bipolar affective disorder were standardised for age and stratified by gender and ethnic group across the three areas.
Results The incidence rate per 100 000 per year in south-east London was over twice that in Nottingham and Bristol. There was no significant difference in the rates of disorder in men and women. Incidence rates of bipolar disorder in the combined Black and minority ethnic groups in all three areas were significantly higher than those of the comparison White groups.
Conclusions The incidence of bipolar disorder was higher in south-east London than in the other two areas, and was higher among Black and minority ethnic groups than in the White population.
![]() |
INTRODUCTION |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
There is evidence to suggest that the incidence of bipolar affective disorder, like that of schizophrenia, may be greater in minority ethnic populations (Leff et al, 1976; Der & Bebbington, 1987; Van Os et al, 1996). With the exception of the study by Leff et al (1976), that had a prospective arm, the cited studies had a predominantly retrospective case-note design, which relied upon information and classification recorded by the psychiatrist at initial contact. Defining and estimating the population at risk was also problematic in the majority of these studies, as before 1991 there was no nationally collected data source that estimated the African-Caribbean population. Therefore previous reported differences could have been due to bias in case definition and ascertainment, or errors in estimation of the population at risk.
In this study we used a prospective approach within well-defined catchment areas using operationalised diagnostic criteria to calculate the incidence of operationally defined bipolar affective disorder in three UK areas. We intended to investigate the relative occurrence of the disorder in men and women, and to compare the incidence in different ethnic groups, taking into account the age structure of these populations.
![]() |
METHOD |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
Population at risk
People aged 16-64 years were eligible if they lived in the geographical
areas comprising the city of Nottingham, Lambeth and the southern two-thirds
of Southwark in south-east London, and central Bristol. The sizes of the
populations at risk were estimated from the 2001 census
(National Statistics, 2002),
which included raw data for ethnic minority groups. In the previous 1991
census (Office of Population Censuses and
Surveys, 1992), there were significant albeit well-characterised
problems in these data regarding the under-enumeration of young adults,
particularly men, from some minority ethnic groups. The 2001 census has
attempted to account for this under-enumeration in its one number
census protocol (Pereira,
2002), thereby negating the need for adjustment of the census data
using under-enumeration correction figures.
Case ascertainment and assessment
We screened all those who presented for the first time to any psychiatric
service (including adult community mental health teams, in-patient units,
forensic services, learning disability services, adolescent mental health
services and drug and alcohol units) because of psychotic phenomena, including
those with possible negative syndrome schizophrenia and non-psychotic
mania.
The ÆSOP study team regularly contacted all service bases that would have received primary care or other referrals to identify eligible participants, and reviewed all admissions with appropriate staff. Furthermore, a leakage study based upon the methods used by Cooper et al (1987) was undertaken after the survey period closed in order to maximise the proportion of true cases included. All relevant mental health information systems were interrogated in order to identify people with a psychotic diagnosis or non-psychotic mania, including drug-induced psychosis or schizotypal, schizoid or paranoid personality disorder. In addition, staff were provided with a list of cases from their area and asked to recall any patients not included. The charts of all potential participants thus identified in Nottingham and south-east London were scrutinised and everyone eligible for referral during the study was identified and asked if they would take part. In Bristol, ethical approval was not obtained for this aspect of the study, so the leakage study was not carried out there. An over-inclusive psychosis screening instrument (Jablensky et al, 1992) was used to screen all the individuals identified in this case ascertainment procedure and identify those who were experiencing delusions, hallucinations, thought disorder, negative features of schizophrenia or features of the manic syndrome. Those who were experiencing any of these, regardless of putative cause, were included as cases in our study.
People who gave informed consent, including those identified in the leakage study, underwent extensive assessment using standardised instruments. These included the Schedule for Clinical Assessment in Neuropsychiatry (SCAN; World Health Organization, 1992), the Schedule for Assessment of Negative Symptoms (SANS; Andreasen, 1982), a modified Personal and Psychiatric History Schedule (PPHS; World Health Organization, 1992), which included collateral information from a relative or carer and a schedule developed for the study for the recording of socio-demographic data. In south-east London and Nottingham, if patients declined to be interviewed the SCAN interview was replaced with the accompanying Item Group Checklist (World Health Organization, 1992), based on material in the case notes and information from clinical staff. There was no ethnic group difference in the proportions of those who declined to be interviewed. In Bristol it was not possible to study detailed information in the case notes of patients who declined to take part in the study, owing to restrictions imposed by the local ethics committee. In these cases a member of the ÆSOP study team established broad diagnoses (no psychosis; non-affective psychosis; mania; psychotic depression) following discussion with the treating clinician at first contact.
Consensus diagnoses were made for each case by a group of clinicians from multicultural backgrounds, with experience in cross-cultural diagnoses, who were involved in the study. This included the researcher who conducted the original individual assessments. Clinical information was presented by the researcher to the diagnostic panel masked to the ethnicity of the patient concerned. Diagnostic codes were assigned in each case according to ICD-10 (World Health Organization, 1993) using all other information from the case notes, item ratings in SCAN and collateral histories.
Reliability of the diagnostic process
Reliability studies were conducted across all three centres for consensus
diagnoses. The principal investigators in each centre produced independent
ratings on 20 cases, which were chosen at random from the entire sample.
Interrater reliability was established between raters, which gave kappa scores
ranging from 0.6 to 0.8. Pre-study reliability was established for the SCAN
interview, which involved the independent rating of videotaped patient
interviews by all relevant researchers, who were trained in Nottingham as part
of a World Health Organization-approved course.
Case definition and ethnicity categorisation in the numerator
Individuals who received a consensus ICD-10 diagnosis of manic episode with
(F30.2) or without (F30.1) psychotic symptoms, including those who had
experienced a previous non-psychotic depressive episode (F31.1, F31.2, F31.6),
were defined as cases and ascribed a diagnosis of bipolar affective disorder
for the purposes of this study. Participants were categorised into ethnic
groupings according to a six-category classification of ethnicity (White;
mixed; Asian; African-Caribbean and Black, any other background; Black
African; any other), modified from the Office for National Statistics
11-category classification (National
Statistics, 2003). The mixed group is a new ethnic
category introduced in the 2001 census that includes all individuals of mixed
heritage. People of Indian, Pakistani and Bangladeshi descent were grouped
together in the Asian category, and similarly, people classified
as Black, any other background were grouped with African-Caribbean
individuals. We merged these groups for clarity of presentation, because their
individual incidence rates were similar and to maximise our statistical power,
although we acknowledge that they retain distinct cultural identities.
Self-ascribed ethnic identity was collected within the socio-demographic
interview and overrode all other data sources. Where this was not available,
when the person had declined to be interviewed, other sources were used. The
most useful was self-ascribed ethnicity collected clinically for the purpose
of clinical care and management returns. Other sources were observer-rated
ethnicity, place of birth and place of parents' birth; where there was
ambiguity, a consensus rating was made by members of the ÆSOP study
team. These methods have been previously used in epidemiological studies of
psychosis, where they have been described in more detail
(Jablensky et al,
1992; Cooper et al,
1987; Brewin et al,
1997; Harrison et al,
1997).
Population at risk
Estimates of the populations at risk were derived using the 2001 census of
Great Britain, which included raw data for minority ethnic groups
(National Statistics, 2002).
People aged 16-64 years who were resident in one of the 32 Census Area
Statistic wards comprising Lambeth and two-thirds of Southwark in south-east
London, the 95 wards of the city of Nottingham, and 52 wards in central
Bristol at the time of the census (29 April 2001) were included in the
population at risk for the purposes of our analysis. Census Area Statistic
wards were introduced in 1998 by the British government to supersede electoral
wards for census enumeration.
The population figures were adjusted according to the length of the study period in each centre in order to obtain an appropriate denominator. Thus, the census population was doubled in south-east London and Nottingham (24-month study period), whereas in Bristol, where cases were recruited over a 9-month period, the census population was multiplied by 0.75.
Statistical analysis
Incidence rates for bipolar affective disorder were calculated,
standardised for age and gender and stratified by gender and ethnicity across
the three centres. The rates were adjusted for age and gender using the
indirect method of standardisation (ISTDIZE;
Stata, 2003) to the 2001
population of England and Wales. This is the preferred method of
standardisation when rates are based upon small numbers in certain strata
(Breslow & Day, 1987). Age
was coded into five strata (16-19, 20-29, 30-39, 40-49 and 50-64 years), and
two separate definitions of ethnicity were considered: White v. Black
and minority ethnic groups, as adopted by the National Institute for Mental
Health in England (2003), and
the six-category classification of ethnicity described above.
![]() |
RESULTS |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
|
Incidence rates and rate ratios
The standardised incidence rates for bipolar affective disorder in the
south-east London, Nottingham and Bristol samples are given in
Table 2. The age-standardised
incidence rate of bipolar affective disorder in south-east London (6.2;
4.5-8.4) was more than double the rate in Nottingham (3.0, 95% CI 2.0-4.4) and
Bristol (1.7, 95% CI 0.5-4.1). Overall, there was no significant difference in
the incidence rate of the disorder between men and women (0.99, 95% CI
0.63-1.56), a consistent effect in each area.
|
The incidence rate for the combined Black and minority ethnic group (12.3, 95% CI 8.3-17.6) was significantly higher than that in the White group (2.3, 95% CI 1.6-3.2). African-Caribbean (18.2, 95% CI 10.8-28.8), Black African (11.9, 95% CI 5.9-21.3) and mixed ethnicity groups had particularly high overall incidence rates of bipolar affective disorder (12.7, 95% CI 4.6-27.8) compared with the White group (2.3, 95% CI 1.6-3.2).
The corresponding rate ratios for the overall sample with 95% confidence intervals are given in Table 3. The incidence rate ratios were elevated in all the ethnic minority groups compared with the White group, but particularly so in the African-Caribbean (7.3, 95% CI 4.0-13.2), Black African (6.4, 95% CI 3.4-12.1) and mixed ethnicity (4.9, 95% CI 1.9-12.5) groups.
|
Table 4 displays the adjusted incidence rate ratios for bipolar affective disorder stratified by ethnicity and centre and shows increased incidence rate ratios for the disorder in certain Black and minority ethnic groups in Bristol and Nottingham compared with south-east London. The rate ratios were higher in Black African, Asian and mixed ethnicity groups in Nottingham, and in African-Caribbean and Black African groups in Bristol compared with south-east London. Incidence rates of bipolar affective disorder among the White population were somewhat higher in south-east London (3.0, 95% CI 1.7-5.1) than in Nottingham (2.2, 95% CI 1.3-3.5) and Bristol (1.1, 95% CI 0.2-3.3).
|
We calculated incidence rate ratios for Nottingham and Bristol using the south-east London incidence figures as a baseline and added an ethnicity stratum to the standardisation procedure in order to determine if the high rates in London might be related to differences in ethnic diversity. Our results suggested that ethnic variation probably accounts for some but not all of this difference, with incidence rate ratios (south-east London as baseline) for Nottingham and Bristol being 0.8 (95% CI 0.5-1.3) and 0.5 (95% CI 0.2-1.2) respectively after adjustment for ethnicity.
![]() |
DISCUSSION |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
Methodological issues
This study has a number of strengths. We employed a prospective design and
used standardised assessments of psychopathology and operational diagnostic
criteria. All three samples were collected from geographically defined
catchment areas and relied upon direct estimates of the population at risk.
The 2001 census data is temporally closest to the study period and included
self-ascribed ethnicity and place of birth. The population data were
pre-adjusted for under-enumeration. All first-contact patients rather than
just first-admission patients were included, and attempts were made to
identify any individuals missed by the referral and screening process through
the leakage protocol.
A number of methodological issues merit attention. People who had never made contact with psychiatric services were not included in the study. It is therefore likely that we missed cases of bipolar spectrum disorder with brief or minor manic symptoms (bipolar II disorder), which are often managed in the community by general practitioners or possibly remain undiagnosed. Strictly, we have defined the administrative incidence of the more severe bipolar disorders. This will be closer to the true population incidence than would the administrative incidence of spectrum disorders where many subjects may not seek help. Differential use of health and psychiatric services by Black and minority ethnic populations compared with White people in our study might also have had an influence on our inception rates (Harrison, 1984). Cooper et al (1987) have suggested that most patients in the UK with severe mental illness are eventually referred to psychiatric services, although among the mobile population of the inner-city areas this may result in presentation out of the geographical area where the illness first developed. However, if such cases are more likely to involve people from Black and minority ethnic groups, this would make our calculated rate ratios, if anything, slight underestimates.
Case definition is particularly problematic in research into bipolar affective disorder as it is difficult to establish the incidence of a disorder that can only be recognised at an unpredictable point in its course, i.e. when polarity changes. For the purposes of this study we accepted modern definitions, which assume bipolarity on the basis of a single episode of mania (Goodwin & Jamison, 1990; Angst, 1998). Differences in illness presentation are therefore likely to result in failure to identify people presenting with initial depressive episodes who have not yet experienced their first manic episode. It is possible that initial presentation bias might account for some of the inflated risk of bipolar affective disorder in minority ethnic groups, as it has been suggested that Black African and African-Caribbean individuals with this disorder might present more frequently with initial manic episodes compared with their White British counterparts (Kirov & Murray, 1999).
Comparison of findings with earlier studies
Our overall incidence figures for bipolar affective disorder are comparable
with those reported in previous studies
(Spicer et al, 1973; Leff et al, 1976;
Daly et al, 1995;
Veijola et al, 1996; Rasanen et al, 1998).
The first contact rate of bipolar affective disorder in Nottingham is similar
to previous rates published by Brewin et al
(1997), whose study was
conducted within approximately the same catchment area using a similar method.
The latter study, however, found a considerable difference in rates between
men and women, a finding not apparent in our sample. Indeed, in contrast to
our study, a number of previous studies have reported an increased incidence
of mania in women compared with men
(Spicer et al, 1973;
Der & Bebbington, 1987; Daly et al, 1995).
However differences might be less apparent in these studies once sampling
error is taken into account.
Interpretation of results across centres
Our results suggest that the increased incidence rates of bipolar affective
disorder in south-east London compared with Nottingham and Bristol might be
partly explained by the higher proportion of individuals from certain Black
and minority ethnic backgrounds in this area compared with the other two
centres. However, it is important to remember that numerous other factors
distinguish the wards of Lambeth and Southwark from Nottingham and Bristol.
Higher levels of deprivation, residential mobility and the social pressures of
inner-city living together with factors relating to availability and
resourcing of local services in south-east London may be of importance in
influencing first-contact rates in this area. Incidence rates among the White
population were also somewhat higher in south-east London, which accords with
the latter hypothesis.
Interactions between bipolar affective disorder and ethnicity
The raised incidence of bipolar affective disorder in Black and minority
ethnic groups in all three samples is in keeping with previous similar
findings from the UK (Leff et al,
1976; Bebbington et
al, 1981; Der &
Bebbington, 1987; Van Os
et al, 1996). Leff et al
(1976) reported high rates of
mania and hypomania among the African-Caribbean population living in
south-east London. This group showed significantly higher rates than the White
group and more often displayed mixed manic and schizophrenic symptoms. Der
& Bebbington (1987) and Van
Os et al (1996) have
confirmed these findings. Furthermore, we found higher rate ratios of bipolar
affective disorder particularly in Black and minority ethnic groups in
Nottingham and Bristol compared with south-east London. One possibility is
that there might be an inverse relationship between the relative size of the
ethnic population within a city and the risk of developing bipolar affective
disorder; this finding has already been described for schizophrenia by Boydell
et al (2001), who
reported a higher incidence of the latter disorder among members of ethnic
minorities living in south-east London wards that had a lower percentage of
ethnic minority inhabitants.
![]() |
Clinical Implications and Limitations |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
LIMITATIONS
![]() |
ACKNOWLEDGMENTS |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
![]() |
REFERENCES |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
Angst, J. (1998) The emerging epidemiology of hypomania and bipolar II disorder. Journal of Affective Disorders, 50, 143 -151.[CrossRef][Medline]
Bebbington, P., Hurry, J. & Tennant, C. (1981) Psychiatric disorders in selected immigrant groups in Camberwell. Social Psychiatry, 16, 43-51.[CrossRef]
Boydell, J., van Os, J., McKenzie, K., et al (2001) Incidence of schizophrenia in ethnic minorities in London: ecological study into interaction with environment. BMJ, 232, 1336 -1338.
Breslow, N. F. & Day, N. E. (1987) Statistical methods in cancer research. II. The design and analysis of cohort studies. IARC Scientific Publications, 82, 1-406.
Brewin, J., Cantwell, R., Dalkin, T., et al (1997) Incidence of schizophrenia in Nottingham. A comparison of two cohorts, 1978-1980 and 1992-1994. British Journal of Psychiatry, 171, 140 -144.[Abstract]
Cooper, J. E., Goodhead, D., Craig, T., et al (1987) The incidence of schizophrenia in Nottingham. British Journal of Psychiatry, 151, 619 -626.[Abstract]
Daly, I., Webb, M. & Kaliszer, M. (1995) First admission incidence study of mania, 1975-1981. British Journal of Psychiatry, 167, 463 -468.[Abstract]
Der, G. & Bebbington, P. (1987) Depression in inner London: a register study. Social Psychiatry, 22, 73-84.[CrossRef][Medline]
Goodwin, G. M. (2000) Bipolar disorder: is psychiatry's Cinderella starting to get out a little more? Acta Neuropsychiatrica, 12, 105 .
Goodwin, F. K. & Jamison, K. R. (1990) Manic Depressive Illness, p. 66 . New York: Oxford University Press.
Harrison, G., Ineichen, B., Smith, J., et al (1984) Psychiatric hospital admission in Bristol. II. Social and clinical aspects. British Journal of Psychiatry, 145, 605 -611.[Abstract]
Harrison, G., Glazebrook, C., Brewin, J., et al (1997) Increased incidence of psychotic disorder in migrants from the Caribbean to the United Kingdom. Psychological Medicine, 27, 799 -806.[CrossRef][Medline]
Jablensky, A., Sartorius, N., Ernberg, G., et al (1992) Schizophrenia: manifestations, incidence and course in different cultures. A World Health Organisation ten country study. Psychological Medicine Monograph Supplement 20.
Kirov, G. & Murray, R. M. (1999) Ethnic differences in the presentation of bipolar affective disorder. European Psychiatry, 14, 199 -204.[CrossRef][Medline]
Leff, J. P., Fischer, M. & Bertelsen, A. (1976) A cross-national epidemiological study of mania. British Journal of Psychiatry, 129, 428 -442.[Abstract]
Lloyd, T. & Jones, P. B. (2002) The epidemiology of first-onset mania. In Textbook in Psychiatric Epidemiology (2nd edn) (eds M. T. Tsuang & M. Tohen), pp. 445 -458. New York: Wiley-Liss.
National Institute for Mental Health in England (2003) Inside Outside: Improving Mental Health Services for Black and Minority Ethnic Communities in England. Leeds: Department of Health.
National Statistics (2002) Census 2001. London: HMSO.
National Statistics (2003) Ethnic Group Statistics: A Guide for the Collection and Classification of Ethnicity Data. London: National Statistics.
Office of Population Censuses and Surveys (1992) Census 1991. London: HMSO.
Pereira, R. (2002) The Census Coverage Survey - The Key Elements of a One Number Census. Titchfield: Office for National Statistics.
Rasanen, P., Tiihonen, J. & Hakko, H. (1998) The incidence and onset-age of hospitalized bipolar affective disorder in Finland. Journal of Affective Disorders, 48, 63 -68.[CrossRef][Medline]
Spicer, C. C., Hare, E. H. & Slater, E. (1973) Neurotic and psychotic forms of depressive illness: evidence from age incidence in a national sample. British Journal of Psychiatry, 123, 535 -541.[Medline]
Stata (2003) STATA Statistical Software, version 8. College Station, TX: StataCorp.
Van Os, J., Castle, D. J., Takei, N., et al (1996) Psychotic illness in ethnic minorities: clarification from the 1991 census. Psychological Medicine, 26, 203 -208.[Medline]
Veijola, J., Rasanen, P. & Isohanni, M. (1996) Low incidence of mania in northern Finland. British Journal of Psychiatry, 168, 520 -521.
World Health Organization (1992) Schedule for Clinical Assessment in Neuropsychiatry. Geneva: WHO.
World Health Organization (1993) The ICD-10 Classification of Mental and Behavioural Disorders. Diagnostic Criteria for Research. Geneva: WHO.
Received for publication May 13, 2004. Revision received September 16, 2004. Accepted for publication September 29, 2004.