Geographical variation in rates of common mental disorders in Britain: prospective cohort study.

BACKGROUND There is little geographical variation in the prevalence of the common mental disorders. However, there is little longitudinal research. AIMS To estimate variance in rates of common mental disorders at individual, household and electoral ward levels prospectively. METHOD A 12-month cohort study of 7659 adults aged 16-74 years in 4338 private households, in 626 electoral wards. Data were collected as part of the British Household Panel Survey. Common mental disorders were assessed using the 12-item General Health Questionnaire (GHQ). Ward-level socio-economic deprivation was measured using the Carstairs index. RESULTS Less than 1% of total variance, in onset and maintenance of common mental disorders and change in GHQ score between waves, occurred at ward level. However, 12% of variance, which is a statistically significant difference, was found at household level (a much smaller geographical unit) and this difference remained after further analyses. CONCLUSIONS Ward level socio-economic deprivation does not influence the onset and maintenance of common mental disorders in Britain but local factors at the household level do. Reasons for this remain unclear.