Season of birth and schizophrenia - an equatorial study.

Studies in the northern and southern hemispheres have generally demonstrated an association between shcizophrenia and winter birth. No previous study has been performed in an equatorial region. The present study investigated the distribution of births of 3,508 schizophrenic patients born in the Philippines. A 15% excess above expectation was found for patients born in the coldest 3-month period of the year (December-February). An excess of births in that period was found in both sexes and in each decade of birth examined. The hypothesis that schizophrenics have a greater sensitivity to those physiological factors which determine conception in the general population is not supported.