Season of birth bias and bulimia nervosa--results from a multi-centre collaboration.

BACKGROUND

Season of birth bias has been observed for people with a number of disorders, including women with bulimia nervosa. However, inconsistent results and methodological weaknesses render previous conclusions about such bias uncertain. With an enhanced methodology, this study aims to test whether there is a season of birth bias for women with bulimia nervosa.

METHOD: Women with bulimia nervosa at five secondary and tertiary services in Norway, born between 1966 and 1988 (n = 549), were compared with women in the general population in a chi-square test for contingency tables, with known population parameters testing monthly deviations.

RESULTS

There was no statistically significant association between month of birth and the distribution of births in the two groups (Cramer's V = .09).

CONCLUSION

There appears not to be any season of birth bias in women with bulimia nervosa in Norway.