Schizophrenia and city residence.

It has long been thought that rates of mental illness are higher in cities than elsewhere, because of crowding and resultant stress. In the case of schizophrenia, there are some marked exceptions to generally higher prevalence rates in industrialised cities. Factors such as migration, culture, infectious disease, demographic rates, and other social processes may affect geographical differences in rates. The excess of schizophrenia in central city areas has been given two opposing explanations--the 'breeder' hypothesis and 'social drift'. Data on incidence from three cities are compared, but do not reveal a clear common picture. Environmental factors connected with urban living are of two main types--social and non-social--which are not mutually exclusive; 'urban' may also have a variety of meanings. Rather than 'urbanicity' being an independent aetiological factor in schizophrenia, its effect may be largely explained in terms of migration and social class.