FLUCTUATIONS IN SCHIZOPHRENIC BIRTHS BY YEAR

Background. It has previously been reported that births of individuals who later develop schizophrenia vary by birth year. Method. Birth dat a were analysed on 34 024 individuals diagnosed with DSM-III-R disorga nised, catatonic, and undifferentiated schizophrenia using time series analysis. Results. Minor yearly fluctuations were observed but did no t achieve statistical significance. Thus earlier findings reported in the literature could not be replicated using a different statistical a pproach. Conclusion. The findings do not support theories which assume major yearly fluctuations in the births of individuals with schizophr enia. Such theories include the perinatal effects of influenza, temper ature variation, and the effects of severe weather.