Seasonality of births in affective disorder in an Irish population

Seasonal variation in the births of patients with schizophrenia is a consis tently replicated epidemiological finding. Few studies have investigated th is phenomenon among patients with a diagnosis of affective disorder. The ma jority of season of birth studies have employed the chi square test for sta tistical analysis, a method that has been subject to some criticism. Using a Kolgomorov-Smirnov type statistic, the quarterly birth distribution of 6, 646 patients with an ICD 9/10 diagnosis of affective disorder were compared to the general population. Only the births of those individuals with unipo lar forms of affective disorder (n = 4,393) differed significantly from the general population, with significant excesses and deficits in the second q uarter and fourth quarter respectively. These results were not altered by a pplication of the displacement test. (C) 1998 Elsevier, Paris.