Childhood abuse and psychotic experiences - evidence for mediation by adulthood adverse life events.

AIMS: We have previously reported an association between childhood abuse and psychotic experiences (PEs) in survey data from South East London. Childhood abuse is related to subsequent adulthood adversity, which could form one pathway to PEs. We aimed to investigate evidence of mediation of the association between childhood abuse and PEs by adverse life events. METHODS: Data were analysed from the South East London Community Health Study (SELCoH, n = 1698). Estimates of the total effects on PEs of any physical or sexual abuse while growing up were partitioned into direct (i.e. unmediated) and indirect (total and specific) effects, mediated via violent and non-violent life events. RESULTS: There was strong statistical evidence for direct (OR 1.58, 95% CI: 1.19-2.1) and indirect (OR 1.51, 95% CI: 1.32-1.72) effects of childhood abuse on PEs after adjustment for potential confounders, indicating partial mediation of this effect via violent and non-violent life events. An estimated 47% of the total effect of abuse on PEs was mediated via adulthood adverse life events, of which violent life events made up 33% and non-violent life events the remaining 14%. CONCLUSIONS: The association between childhood abuse and PEs is partly mediated through the experience of adverse life events in adulthood. There is some evidence that a larger proportion of this effect was mediated through violent life events than non-violent life events.

Tobacco smoking is associated with psychotic experiences in the general population of South London.

BACKGROUND: The association between cigarette smoking and psychosis remains unexplained, but could relate to causal effects in both directions, confounding by socioeconomic factors, such as ethnicity, or use of other substances, including cannabis. Few studies have evaluated the association between cigarettes and psychotic experiences (PEs) in diverse, inner-city populations, or relationships with number of cigarettes consumed. METHODS: We assessed associations and dose-response relationships between cigarette smoking and PEs in a cross-sectional survey of household residents (n = 1680) in South East London, using logistic regression to adjust for cannabis use, other illicit substances, and socioeconomic factors, including ethnicity. RESULTS: We found association between any PEs and daily cigarette smoking, which remained following adjustment for age, gender, ethnicity, cannabis and use of illicit stimulant drugs (fully adjusted odds ratio 1.47, 95% confidence interval 1.01-2.15). Fully adjusted estimates for the association, and with number of PEs, increased with number of cigarettes smoked daily, implying a dose-response effect (p = 0.001 and <0.001, respectively). Odds of reporting any PEs in ex-smokers were similar to never-smokers. CONCLUSIONS: In this diverse epidemiological sample, association between smoking and PEs was not explained by confounders such as cannabis or illicit drugs. Daily cigarette consumption showed a dose-response relationship with the odds of reporting PEs, and of reporting a greater number of PEs. There was no difference in odds of reporting PEs between ex-smokers and never-smokers, raising the possibility that the increase in PEs associated with smoking may be reversible.

The effect of the environment on symptom dimensions in the first episode of psychosis: a multilevel study.

BACKGROUND: The extent to which different symptom dimensions vary according to epidemiological factors associated with categorical definitions of first-episode psychosis (FEP) is unknown. We hypothesized that positive psychotic symptoms, including paranoid delusions and depressive symptoms, would be more prominent in more urban environments. METHOD: We collected clinical and epidemiological data on 469 people with FEP (ICD-10 F10-F33) in two centres of the Aetiology and Ethnicity in Schizophrenia and Other Psychoses (AESOP) study: Southeast London and Nottinghamshire. We used multilevel regression models to examine neighbourhood-level and between-centre differences in five symptom dimensions (reality distortion, negative symptoms, manic symptoms, depressive symptoms and disorganization) underpinning Schedules for Clinical Assessment in Neuropsychiatry (SCAN) Item Group Checklist (IGC) symptoms. Delusions of persecution and reference, along with other individual IGC symptoms, were inspected for area-level variation. RESULTS: Reality distortion [estimated effect size (EES) 0.15, 95% confidence interval (CI) 0.06-0.24] and depressive symptoms (EES 0.21, 95% CI 0.07-0.34) were elevated in people with FEP living in more urban Southeast London but disorganized symptomatology was lower (EES -0.06, 95% CI -0.10 to -0.02), after controlling for confounders. Delusions of persecution were not associated with increased neighbourhood population density [adjusted odds ratio (aOR) 1.01, 95% CI 0.83-1.23], although an effect was observed for delusions of reference (aOR 1.41, 95% CI 1.12-1.77). Hallucinatory symptoms showed consistent elevation in more densely populated neighbourhoods (aOR 1.32, 95% CI 1.09-1.61). CONCLUSIONS: In people experiencing FEP, elevated levels of reality distortion and depressive symptoms were observed in more urban, densely populated neighbourhoods. No clear association was observed for paranoid delusions; hallucinations were consistently associated with increased population density. These results suggest that urban environments may affect the syndromal presentation of psychotic disorders.

Modelling the interplay between childhood and adult adversity in pathways to psychosis: initial evidence from the AESOP study.

BACKGROUND: There is evidence that a range of socio-environmental exposures is associated with an increased risk of psychosis. However, despite the fact that such factors probably combine in complex ways to increase risk, the majority of studies have tended to consider each exposure separately. In light of this, we sought to extend previous analyses of data from the AESOP (Aetiology and Ethnicity in Schizophrenia and Other Psychoses) study on childhood and adult markers of disadvantage to examine how they combine to increase risk of psychosis, testing both mediation (path) models and synergistic effects. METHOD: All patients with a first episode of psychosis who made contact with psychiatric services in defined catchment areas in London and Nottingham, UK (n = 390) and a series of community controls (n = 391) were included in the AESOP study. Data relating to clinical and social variables, including parental separation and loss, education and adult disadvantage, were collected from cases and controls. RESULTS: There was evidence that the effect of separation from, but not death of, a parent in childhood on risk of psychosis was partially mediated through subsequent poor educational attainment (no qualifications), adult social disadvantage and, to a lesser degree, low self-esteem. In addition, there was strong evidence that separation from, but not death of, a parent combined synergistically with subsequent disadvantage to increase risk. These effects held for all ethnic groups in the sample. CONCLUSIONS: Exposure to childhood and adult disadvantage may combine in complex ways to push some individuals along a predominantly sociodevelopmental pathway to psychosis.

Unemployment, ethnicity and psychosis.

OBJECTIVE: This study describes the incidence of psychosis in unemployed people and determines whether unemployment has a greater impact on the development of psychosis amongst Black minority groups than White groups. METHOD: Patients with a first diagnosis of Research Diagnostic Criteria psychosis, in a defined area of London from 1998 to 2004, were identified. Crude and standardised incidence rates of psychosis amongst unemployed people for each ethnic group were calculated. Poisson regression modelling tested for interactions between unemployment and ethnicity. RESULTS: Hundred cases occurred amongst employed people and 78 cases occurred amongst the unemployed people. When standardised to the employed White population of the area, White unemployed people had a standardised incidence ratio (SIR) of 11.7 (95% CI 6.4-19.7), Black Caribbean people had a SIR of 60.1(95% CI 39.3-88) and Black African people had a SIR of 40.7 (95% CI 25.8-61.1). There was no interaction however between ethnicity and unemployment (Likelihood ratio test P = 0.54). CONCLUSION: Rates of psychosis are high amongst unemployed people in south London and extremely high amongst Black Caribbean and Black African unemployed people. There was no evidence however that the minority groups were particularly sensitive to the stresses, limitations or meaning of unemployment.

First-episode psychosis at the West Bologna Community Mental Health Centre: results of an 8-year prospective study.

BACKGROUND: Research mostly conducted in the UK and northern Europe has established that there are high rates of first-episode psychosis (FEP) in large cities and immigrant populations; moreover, psychosis has been found to be associated with cannabis use and early trauma. The present study aimed to evaluate the incidence rate of FEP and the distribution of several risk factors (e.g. age, ethnicity, substance abuse) in Bologna, Italy. METHOD: The Bologna FEP (BoFEP) study is an 8-year prospective study. All FEP patients, 18-64 years old, consecutively referred to the West Bologna Community Mental Health Centre (CMHC) from 2002 to 2009 were evaluated. Sociodemographic information, migration history and clinical data were collected through an ad-hoc schedule. Psychiatric diagnoses were recorded using the Schedule for Clinical Assessment of Neuropsychiatry (SCAN). RESULTS: The overall incidence rate (IR) in the BoFEP study was 16.4 per 100 000 person-years [95% confidence interval (CI) 13.9-18.9]. The incidence was higher in young people, men and migrants (MI). CONCLUSIONS: The IR of FEP found by the Bologna study is lower than that found by other European studies. However, as in other studies, the incidence was higher in certain groups. This heterogeneity has implications for policy and mental health service development, and for understanding the aetiology of psychosis.

Mortality in first-contact psychosis patients in the U.K.: a cohort study.

BACKGROUND: The excess mortality following first-contact psychosis is well recognized. However, the causes of death in a complete incidence cohort and mortality patterns over time compared with the general population are unknown. METHOD: All 2723 patients who presented for the first time with psychosis in three defined catchment areas of the U.K. in London (1965-2004, n=2056), Nottingham (1997-1999, n=203) and Dumfries and Galloway (1979-1998, n=464) were traced after a mean of 11.5 years follow-up and death certificates were obtained. Data analysis was by indirect standardization. RESULTS: The overall standardized mortality ratio (SMR) for first-contact psychosis was 184 [95% confidence interval (CI) 167-202]. Most deaths (84.2%, 374/444) were from natural causes, although suicide had the highest SMR (1165, 95% CI 873-1524). Diseases of the respiratory system and infectious diseases had the highest SMR of the natural causes of death (232, 95% CI 183-291). The risk of death from diseases of the circulatory system was also elevated compared with the general population (SMR 139, 95% CI 117-164) whereas there was no such difference for neoplasms (SMR 111, 95% CI 86-141). There was strong evidence that the mortality gap compared with the general population for all causes of death (p<0.001) and all natural causes (p=0.01) increased over the four decades of the study. There was weak evidence that cardiovascular deaths may be increasing relative to the general population (p=0.07). CONCLUSIONS: People with first-contact psychosis have an overall mortality risk that is nearly double that of the general population. Most excess deaths are from natural causes. The widening of the mortality gap over the last four decades should be of concern to all clinicians involved in delivering healthcare.

Ethnicity, social disadvantage and psychotic-like experiences in a healthy population based sample.

OBJECTIVE: We sought to investigate the prevalence and social correlates of psychotic-like experiences in a general population sample of Black and White British subjects. METHOD: Data were collected from randomly selected community control subjects, recruited as part of the AESOP study, a three-centre population based study of first-episode psychosis. RESULTS: The proportion of subjects reporting one or more psychotic-like experience was 19% (n = 72/372). These were more common in Black Caribbean (OR 2.08) and Black African subjects (OR 4.59), compared with White British. In addition, a number of indicators of childhood and adult disadvantage were associated with psychotic-like experiences. When these variables were simultaneously entered into a regression model, Black African ethnicity, concentrated adult disadvantage, and separation from parents retained a significant effect. CONCLUSION: The higher prevalence of psychotic-like experiences in the Black Caribbean, but not Black African, group was explained by high levels of social disadvantage over the life course.

Cumulative social disadvantage, ethnicity and first-episode psychosis: a case-control study.

BACKGROUND: Numerous studies have reported high rates of psychosis in the Black Caribbean population in the UK. Recent speculation about the reasons for these high rates has focused on social factors. However, there have been few empirical studies. We sought to compare the prevalence of specific indicators of social disadvantage and isolation, and variations by ethnicity, in subjects with a first episode of psychosis and a series of healthy controls. METHOD: All cases with a first episode of psychosis who made contact with psychiatric services in defined catchment areas in London and Nottingham, UK and a series of community controls were recruited over a 3-year period. Data relating to clinical and social variables were collected from cases and controls. RESULTS: On all indicators, cases were more socially disadvantaged and isolated than controls, after controlling for potential confounders. These associations held when the sample was restricted to those with an affective diagnosis and to those with a short prodrome and short duration of untreated psychosis. There was a clear linear relationship between concentrated disadvantage and odds of psychosis. Similar patterns were evident in the two main ethnic groups, White British and Black Caribbean. However, indicators of social disadvantage and isolation were more common in Black Caribbean subjects than White British subjects. CONCLUSIONS: We found strong associations between indicators of disadvantage and psychosis. If these variables index exposure to factors that increase risk of psychosis, their greater prevalence in the Black Caribbean population may contribute to the reported high rates of psychosis in this population.

Testing the association between the incidence of schizophrenia and social capital in an urban area.

BACKGROUND: Social capital has been considered aetiologically important in schizophrenia but the empirical evidence to support this hypothesis is absent. We tested whether social capital, measured at the neighbourhood level, was associated with the incidence of schizophrenia (ICD-10 F20). MethodWe administered a cross-sectional questionnaire on social capital to 5% of the adult population in 33 neighbourhoods (wards) in South London (n=16 459). The questionnaire contained items relating to two social capital constructs: social cohesion and trust (SC&T) and social disorganization (SocD). Schizophrenia incidence rates, estimated using data from the Aetiology and Ethnicity in Schizophrenia and Other Psychoses (AESOP) study, provided the outcome. We used multi-level Poisson regression to test our hypothesis while controlling for individual- and neighbourhood-level characteristics. RESULTS: We identified 148 cases during 565 576 person-years at-risk. Twenty-six per cent of the variation in incidence rates was attributable to neighbourhood-level characteristics. Response from the social capital survey was 25.7%. The association between SC&T and schizophrenia was U-shaped. Compared with neighbourhoods with medial levels of SC&T, incidence rates were significantly higher in neighbourhoods with low [incidence rates ratio (IRR) 2.0, 95% confidence interval (CI) 1.2-3.3] and high (IRR 2.5, 95% CI 1.3-4.8) levels of SC&T, independent of age, sex, ethnicity, ethnic density, ethnic fragmentation and socio-economic deprivation. ConclusionNeighbourhood variation in SC&T was non-linearly associated with the incidence of schizophrenia within an urban area. Neighbourhoods with low SC&T may fail to mediate social stress whereas high SC&T neighbourhoods may have greater informal social control or may increase the risk of schizophrenia for residents excluded from accessing available social capital.

A comparison of symptoms and family history in schizophrenia with and without prior cannabis use: implications for the concept of cannabis psychosis.

BACKGROUND: There is considerable interest in cannabis use in psychosis. It has been suggested that the chronic psychosis associated with cannabis use, is symptomatically distinct from idiopathic schizophrenia. Several studies have reported differences in psychopathology and family history in people with schizophrenia according to whether or not they were cannabis users. We set out to test the hypotheses arising from these studies that cannabis use is associated with more bizarre behaviour, more thought disorder, fewer negative symptoms including blunted affect, more delusions of reference, more paranoid delusions and a stronger family history of schizophrenia. METHOD: We used a case register that contained 757 cases of first onset schizophrenia, 182 (24%) of whom had used cannabis in the year prior to first presentation, 552 (73%) had not and 3% had missing data. We completed the OPCRIT checklist on all patients and investigated differences in the proportion of people with distractibility, bizarre behaviour, positive formal thought disorder, delusions of reference, well organised delusions, any first rank symptom, persecutory delusions, abusive/accusatory hallucinations, blunted affect, negative thought disorder, any negative symptoms (catatonia, blunted affect, negative thought disorder, or deterioration), lack of insight, suicidal ideation and a positive family history of schizophrenia, using chi square tests. Logistic regression modelling was then used to determine whether prior cannabis use affected the presence of the characteristics after controlling for age, sex and ethnicity. RESULTS: There was no statistically significant effect of cannabis use on the presence of any of the above. There remained however a non-significant trend towards more insight (OR 0.65 p=0.055 for "loss of insight") and a finding of fewer abusive or accusatory hallucinations (OR 0.65 p=0.049) of borderline significance amongst the cannabis users. These were in the hypothesised direction. There was no evidence of fewer negative symptoms or greater family history amongst cannabis users. CONCLUSION: We found few appreciable differences in symptomatology between schizophrenic patients who were or were not cannabis users. There were no differences in the proportion of people with a positive family history of schizophrenia between cannabis users and non-users. This argues against a distinct schizophrenia-like psychosis caused by cannabis.

The incidence of schizophrenia in European immigrants to Canada.

OBJECTIVE: The risk for schizophrenia in immigrants to Europe is approximately three times that of native-born populations. Discrimination and marginalization may influence the risk for schizophrenia within migrant populations. The primary objective of the present study was to determine whether the risk associated with migration was also evident 100 years ago. A second objective was to determine whether changing social stresses are associated with changes to the incidence of schizophrenia. METHOD: During the first two decades of the twentieth century, the Provincial Mental Hospital was the sole provider of psychiatric services in British Columbia, Canada. Detailed clinical records have been preserved for 99.5% of 2477 patients who had a psychiatric admission between 1902 and 1913. Diagnoses were made after a detailed file review and 807 patients met DSM-IV criteria for first-episode schizophrenia, schizophreniform disorder, schizoaffective disorder, or psychosis not otherwise specified. Diagnoses had high inter-rater reliability. The incidence of schizophrenia in migrants from Britain or Continental Europe was compared with that in the Canadian-born population using indirect standardization and Poisson models. RESULTS: Migration from Britain or Continental Europe to Canada in the early twentieth century was associated with an increased rate of schizophrenia; IRR=1.54, (95% CI=1.33-1.78). Incidence increased over time in immigrants but not in the native-born population and this increase occurred during a period of economic recession. CONCLUSIONS: Migration was a risk factor for schizophrenia a century ago as it is today. This risk occurred in white migrants from Europe and increased during a period of increased social stress.

Trends in cannabis use prior to first presentation with schizophrenia, in South-East London between 1965 and 1999.

BACKGROUND: There is evidence that cannabis use might be relevant to the aetiology of schizophrenia. We aimed to measure any change in cannabis use over time in those first presenting with schizophrenia in South-East London from 1965 to 1999, and compare this with change in use in those presenting with non-psychotic psychiatric disorders. METHOD: The rate of cannabis use in the year prior to first ever presentation was measured over seven time periods. Logistic regression modelling was used to determine (a) whether cannabis use changed over time, after controlling for age, sex and ethnicity, and (b) whether there was an interaction between diagnosis and time. RESULTS: Cannabis use increased over time in both the schizophrenia group [odds ratio per time period (OR) 2.03, 95% confidence interval (CI) 1.74-2.38, p<0.0001] and the non-psychotic disorders group (OR 1.24, 95% CI 1.05-1.47, p=0.012), after controlling for age, sex and ethnicity. However, the effect of time was significantly greater in the schizophrenia group than in the non-schizophrenia group (chi2=17, p<0.0001). CONCLUSION: Cannabis use in the year prior to presentation with schizophrenia increased markedly between 1965 and 1999, and disproportionately so compared to increase in cannabis use in other psychiatric disorders.

Incidence and distribution of first-episode mania by age: results from a 35-year study.

BACKGROUND: Few epidemiological studies have investigated incidence by age or age at onset distributions for mania or bipolar disorder. The current study aimed to determine these in a defined area in south-east London, over a 35-year period. METHOD: All cases of first-episode mania presenting to psychiatric services in Camberwell, south-east London, between 1965 and 1999 were identified. Incidence rates by age, using 5-year age-at-onset bands, were estimated and the structure of the age-at-onset distribution for first-episode mania was investigated using finite mixture distributions (admixture analysis). RESULTS: The incidence of DSM-IV bipolar I disorder (BP I), first manic episode peaked in early adult life (16.38/100,000 population per year in the 21-25 years band) with a much smaller peak in mid-life. A two-component normal mixture distribution fitted age at onset better than either a single normal distribution or a three-component mixture, implying the existence of early and later onset subgroups. The early onset group had a stronger family history of bipolar disorder, and showed more acute, severe and atypical symptoms during their first manic episode. CONCLUSIONS: The incidence of mania peaks in early adult life but there is clear evidence of early and later onset subgroups which may represent different forms of disorder.

Pathways to care and ethnicity. 1: Sample characteristics and compulsory admission. Report from the AESOP study.

BACKGROUND: Many studies have found high levels of compulsory admission to psychiatric hospital in the UK among African-Caribbean and Black African patients with a psychotic illness. AIMS: To establish whether African-Caribbean and Black African ethnicity is associated with compulsory admission in an epidemiological sample of patients with a first episode of psychosis drawn from two UK centres. METHOD: All patients with a first episode of psychosis who made contact with psychiatric services over a 2-year period and were living in defined areas were included in the (AESOP) study. For this analysis we included all White British, other White, African-Caribbean and Black African patients from the AESOP sampling frame. Clinical, socio-demographic and pathways to care data were collected from patients, relatives and case notes. RESULTS: African-Caribbean patients were significantly more likely to be compulsorily admitted than White British patients, as were Black African patients. African-Caribbean men were the most likely to be compulsorily admitted. CONCLUSIONS: These findings suggest that factors are operating at or prior to first presentation to increase the risk of compulsory admission among African-Caribbean and Black African patients.

Pathways to care and ethnicity. 2: Source of referral and help-seeking. Report from the AESOP study.

BACKGROUND: Previous research has found that African-Caribbean and Black African patients are likely to come into contact with mental health services via more negative routes, when compared with White patients. We sought to investigate pathways to mental health care and ethnicity in a sample of patients with a first episode of psychosis drawn from two UK centres. METHOD: We included all White British, other White, African-Caribbean and Black African patients with a first episode of psychosis who made contact with psychiatric services over a 2-year period and were living in defined areas. Clinical, socio-demographic and pathways to care data were collected from patients, relatives and case notes. RESULTS: Compared with White British patients, general practitioner referral was less frequent for both African-Caribbean and Black African patients and referral by a criminal justice agency was more common. With the exception of criminal justice referrals for Black African patients, these findings remained significant after adjusting for potential confounders. CONCLUSIONS: These findings suggest that factors are operating during a first episode of psychosis to increase the risk that the pathway to care for Black patients will involve non-health professionals.

Ethnic differences in first clinical presentation of bipolar disorder: results from an epidemiological study.

BACKGROUND: Although high incidence rates of mania have been described in some ethnic minority populations, little is known about any ethnic differences in the early clinical presentation of bipolar disorder. METHODS: All cases of operationalised DSM-IV bipolar I disorder (BPI), first manic episode, within a defined epidemiological catchment area over a 35-year period, were identified; sociodemographic data, including ethnicity, and clinical information were then extracted. The proportion of African-Caribbean (n=52), African (n=33) and white European (n=149) cases who experienced a depressive episode before onset of mania and psychotic symptoms at first mania were compared. RESULTS: African-Caribbean and African groups were significantly less likely to have experienced a depressive episode before onset of first mania, at 13.5% and 6.1%, respectively, compared with 28.1% in the white European group. African-Caribbean and African groups also experienced more severe psychotic symptoms at first mania, but there were no differences in mood incongruent or first rank symptoms between ethnic groups. LIMITATIONS: Data pertaining to diagnosis and clinical symptoms were extracted by retrospective case note review. CONCLUSIONS: Ethnic differences in clinical presentation of bipolar disorder may have implications for assessment and treatment of ethnic minority patients.

The association of inequality with the incidence of schizophrenia--an ecological study.

BACKGROUND: Socio-economic factors are known to be associated with schizophrenia, but no studies have investigated the effect of inequality on incidence rates of schizophrenia. The aim of the study was to determine whether those electoral wards with greater inequality have a higher incidence of schizophrenia. METHOD: An ecological study was carried out involving a retrospective case record study to calculate the incidence of schizophrenia across wards in Camberwell, South London for the period 1988-1997, and an index of inequality within each ward was calculated. RESULTS: There was no significant effect of inequality overall. However, in the group of deprived wards, the incidence of RDC schizophrenia increased as inequality increased (IRR 3.79, 95 %CI 1.25.11.49 p = 0.019 after adjusting for age, sex, absolute deprivation, ethnicity, proportion of ethnic minorities and the interaction between individual ethnicity and proportion of ethnic minorities. CONCLUSION: Increased inequality is associated with increasing incidence of schizophrenia, but only in the most deprived areas. This is independent of other known social risk factors.

Incidence of schizophrenia in south-east London between 1965 and 1997.

BACKGROUND: There has been much debate about changes in the incidence of schizophrenia. AIMS: To identify any changes in incidence of schizophrenia in Camberwell, south-east London, between 1965 and 1997. METHOD: Research Diagnostic Criteria and DSM-III-R 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.

Incidence of schizophrenia in ethnic minorities in London: ecological study into interactions with environment.

OBJECTIVE: To determine whether the incidence of schizophrenia among people from non-white ethnic minorities is greater in neighbourhoods where they constitute a smaller proportion of the total population. DESIGN: Ecological design including retrospective study of case records to calculate the incidence of schizophrenia in the ethnic minority population across electoral wards and multi-level analysis to examine interaction between individuals and environment. SETTING: 15 electoral wards in Camberwell, South London. PARTICIPANTS: All people aged 16 years and over who had contact with psychiatric services during 1988-97. MAIN OUTCOME MEASURE: Incidence rates of schizophrenia according to Research Diagnostic Criteria. RESULTS: The incidence of schizophrenia in non-white ethnic minorities increased significantly as the proportion of such minorities in the local population fell. The incidence rate ratio varied in a dose-response fashion from 2.38 (95% confidence interval 1.49 to 3.79) in the third of wards where non-white ethnic minorities formed the largest proportion (28-57%) of the local population to 4.4 (2.49 to 7.75) in the third of wards where they formed the smallest proportion (8-22%). CONCLUSION: The incidence of schizophrenia in non-white ethnic minorities in London is greater when they comprise a smaller proportion of the local population.