We report an analysis of a large catchment area sample of patients with nonaffective functional psychoses presenting across all ages at onset. The male:female ratio was 1.56:1 in the 16-25-year age group; it reached unity around 30 years of age and declined to 0.38:1 in the 66-75-year group. Contrary to expectation, a higher proportion of patients with onset of illness after 45 years than of younger onset patients fulfilled DSM-III-R criteria for schizophrenia (52% vs. 38%). The distribution by age at onset was much the same irrespective of stringency of diagnosis. The highest rates were in the 16-25-year age group, with a slight second peak in the 46-55-year group, and a third (more emphatic) peak in the over-65 group. A closer analysis of demographic and phenomenologic variables revealed distinct differences between patients with early and late (after 44 years) onset of illness.
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Castle et al. (1993) studied this question.