SEASON OF BIRTH AND
A SYSTEMATIC REVIEW AND META-ANALYSIS OF DATA FROM THE SOUTHERN
J.J. McGrath*, J.L. Welham.
Queensland Centre for Schizophrenia Research
Wolston Park Hospital, Wacol 4076, Australia
AIMS: Data from the Northern Hemisphere
supports an excess of winter-spring births of individuals who
later develop schizophrenia when compared to the general
population. The data from the Southern Hemisphere has been less
consistent. This paper will present a systematic review and
meta-analysis of relevant data from the Southern Hemisphere.
METHODS: To identify relevant studies we
searched electronic databases, reviewed citations from target
publications and wrote letters to published authors in the field.
The counts for observed and expected births were assessed in four
planned comparisons. In the absence of significant heterogeneity,
the data were combined using Mantel-Haenzel odds ratio in a fixed
RESULTS: Twelve studies were identified.
Published and unpublished data from 8 of these were able to be
included in the analyses. For the two season comparisons (n =
19,349), small but non-significant excesses were found in the
first comparison (winter versus other seasons; OR=1.04, 95% Cl 0
99-1.09) and for the second comparison (winter and spring versus
other seasons; OR=1.03, 95% cl 0.99-1.08). For the two quarterly
comparisons (n=14,799), there was a small but non-significant
excess found in the third comparison (third quarter versus other
quarters; OR=1.03, 95% Cl 0.98-1.09), and a small but
non-significant deficit in the fourth comparison (third and
fourth quarter versus other quarters, OR=0.99, 95% Cl 0.95-1.04).
CONCLUSIONS: Assuming that season of birth
acts as proxy marker for fluctuating non-genetic risk-modifying
factors for schizophrenia, the results of this review suggest
that in the Southern Hemisphere these factors may be weaker, less
prevalent, less regular, and/or may be modified by other
confounding or modifying variables.
This project was supported by the Stanley