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.