Cross-national differences in the frequency and outcome of schizophrenia: a comparison of five hypotheses.

Measures of morbid risk for schizophrenia derived from the WHO Determinants of Outcome of Severe Mental Disorders Study showed large correlations with the following: an occupational index, a measure of urbanicity, geographical and climatic variables, a dietary measure, and the infant mortality rate. The same variables were also correlated with a measure of outcome derived from the International Pilot Study of Schizophrenia. Nearly all of the correlations were significant. The postulated "explanatory" variables were themselves highly intercorrelated.