Season of birth and schizophrenia: southern hemisphere data.
OBJECTIVE: The association between winter birth and increased incidence of schizophrenia is well documented in the northern hemisphere. The present study examined season of birth and schizophrenia in a southern hemisphere population from a mild temperate climate. METHOD: The seasonal incidence of birth in schizophrenic patients was compared, using Chi-squared tests, to normative population birth rates. RESULTS: A statistically significant seasonal pattern, with a peak in late spring and early summer, was obtained. CONCLUSION: This supports northern hemisphere findings regarding calendar month, but not season, of excess schizophrenic births. This has implications for viral and other aetiological hypotheses dependent on meteorological factors.