Season of birth in schizophrenia: no latitude at the equator.
Level 4 - case-series / case-control
Retrospective case-control study comparing patient birth distributions to population data.
PubMed 10789330 · doi:10.1192/bjp.176.1.68
What was done
The authors examined birth month distributions among 9655 patients born between 1930 and 1984 who were discharged with a diagnosis of schizophrenia from Singapore's national psychiatric hospital. Aggregated data and birth-year subsamples were analyzed for secular trends, and a subsample born between 1960 and 1984 was matched against general population data to assess whether seasonal birth patterns occur in an equatorial region without formal seasons.
What was found
Monthly birth variations were present in both patients and controls, with distributions being largely similar between the groups aside from a trough in patient births during March-April. No seasonal excess was observed among individuals who later developed schizophrenia. The abstract reports no numerical counts, percentages, or test statistics.
Why it matters
These findings support the hypothesis that the winter birth excess observed in schizophrenia is linked to latitude-dependent seasonal factors, as the effect is absent in an equatorial climate without distinct seasons.
Limits
The abstract omits exact statistical figures, effect sizes, and confidence intervals. Findings are based on patients discharged from a single national psychiatric hospital, and exact matching against general population records was restricted to the 1960-1984 birth cohort.
Cited by
- contradicts Schizophrenia is not found in populations near the equator.