In some reports, summer birth has been associated with deficit schizophrenia.
Deficit schizophrenia and nondeficit schizophrenia also differ in several
To conduct a combined analysis of the published and unpublished data
sets from the northern hemisphere that relate deficit and nondeficit schizophrenia
to month of birth.
Studies of season of birth in which it was possible to make a deficit/nondeficit
Published studies with samples of convenience and all known population-based
studies with the deficit/nondeficit categorization were included. The studies
came from 6 countries.
Three published studies of samples of convenience, 2 population-based
prevalence studies, and 5 population-based studies that approximated incident
samples were included. Month of birth was compared for deficit and nondeficit
schizophrenia, using meta-analytic fixed-effects models.
A group x month goodness-of-fit χ2 showed a significant
difference between deficit and nondeficit subjects in season of birth (P < .001) in the studies that approximated
incidence. This difference was largely due to an increase in deficit schizophrenia
births in June and July (odds ratio, 1.9; 95% confidence interval, 1.3-2.9).
Similar results were found in the prevalence studies. A similar pattern was
found in 2 of the 3 samples of convenience, but when combined, these 3 samples
did not show a significant deficit/nondeficit difference.
Deficit schizophrenia has a season of birth pattern that differs from
that of nondeficit schizophrenia. This analysis supports the notion of a separate
disease within schizophrenia.