Social epidemiology studies the link between the social environment and the development and distribution of diseases in populations (Kaufman and Cooper, 1999). Research into social and behavioural determinants of health and illness is an area of interest for both sociologists and social epidemiologists. This section provides an introduction to some design and conceptual issues in social epidemiology and detailed discussion of temporal and geographical variations in the incidence, course and outcome of schizophrenia, with particular emphasis on issues of urbanization and migration.

Epidemiologists are very familiar with individual-level effects or risk factors such as birth complications, smoking or substance misuse. However Bresnahan and Susser in Chapter 1 emphasize the importance of societal-level effects (such as racism or level of socioeconomic development) in elucidating disease trends and mechanisms. The use of age–period–cohort effect analyses and life-course approaches to epidemiology are also included.

One of the central tenets of schizophrenia epidemiology is that the (narrowly defined) disorder appears to occur with equal incidence worldwide. However some variation in incidence rates between the developed and developing world has been noted for broadly defined schizophrenia. Bresnahan and colleagues examine this issue in Chapter 2 but recognize that the question of variation in incidence will remain unresolved ‘while we await incidence rates based on rediagnosis using modern diagnostic systems’.