Various theories have been offered in explanation of the well known fact that the number of male births always exceeds that of female births. Although the biologic processes that ultimately determine the preponderance of males as compared with females at birth are, according to Russell,1 imperfectly understood as yet, it is possible to study the relation to such purely external factors as age, nationality and social status of the parents, and to primogeniture and size of the family, seasonal and secular trend, and the extent to which it is influenced by cross-breeding, migration and social upheavals. Such was the purpose of the study recently reported by Russell.
The statistics on which the investigations were based were obtained from (1) the Annual Reports of the Registrar-General for England and Wales, (2) the Reports on Births and Still Births in the United States, (3) Annuaire international de statistique, and (4) the
THE SEX RATIO AT BIRTH. JAMA. 1936;107(15):1224-1225. doi:10.1001/jama.1936.02770410046013