The seasonality of schizophrenic births: a reply to Marc S. Lewis

Lewis contends that the previously demonstrated finding of seasonality of schizophrenic births is a statistical artifact due to the age-incidence effect. If Lewis is correct, then (1) January should have the highest schizophrenic birthrate, (2) December should have the lowest schizophrenic birthrate, (3) the Southern Hemisphere should show the same pattern as the Northern Hemisphere, and (4) the age-incidence effect should be more marked in younger age cohorts. None of these findings have been borne out by studies to date. It is concluded that the seasonality of schizophrenic birthrates is a replicable finding, and should be considered one of the more intriguing clues to the etiology of this disease.