An Empirical Test of Three Hypotheses concerning the Human Sex Ratio at Birth in the United States, 1915-1948

Abstract

Sex distr. of live births is usually expressed by means of a sex ratio. In the U. S. this is in the neighborhood of 105.6 for the total population. This study investigates the assertions that: (1) sex ratio among live births tends to rise during or after a war; (2) sex ratio among live births tends to decrease as the age of the mother increases; and (3) as the order of birth increases, the sex ratio tends to fall. The materials studied to investigate these assertions were data secured from the vital statistics of the birth-registration area of the United States for the period 1915 to 1948. Based on the sex ratio the data support the hypothes.es that the sex ratio at birth does not consistently change as a direct influence of war either during the war years or immediately thereafter. Among both whites and Negroes there is a tendency for the sex ratio among live births to decrease as the age of the mother increases; however there is no consistent trend. The consistency is greater among whites than among Negroes. The mean sex ratio of all children other than the first born is lower than the mean sex ratio of first born children. Any increase in the sex ratio to above average during World War II can be considered primarily a result of the increase in the proportion of first births rather than a result of a greater proportion of births to young mothers.