Analysis of the seasonal variation of schizophrenic births using a Kolmogorov-Smirnov type statistic

Abstract

SummaryPrevious studies have shown that schizophrenic patients are more likely to be born in winter or early spring months than the general population. Data on 4,207 patients with a hospital diagnosis of schizophrenia were obtained from a mailed survey to public departments of adult psychiatry in metropolitan France. For each year from 1900 to 1965, the expected monthly number of schizophrenic births was calculated and any seasonal variation of live births in the general population was taken into account. Cumulative distributions of the observed and expected number of schizophrenic births were compared using a Kolmogorov-Smirnov type statistic. The seasonal distribution of schizophrenic births was significantly different from that of the general population (P < 0.01). An excess of schizophrenic births was found in the first half of the year, with a peak in April (+ 13%).