Statistical and Mathematical Modeling in Biological Applications
Abstract: The sex ratio at birth (the ratio of male to female births) varies among couples. The study revisits vital registration data from Europe (France, 1946-1955; Saxony, 1875-1884) and demographic survey data from Africa (1930-2005), to estimate the underlying pattern of heterogeneity in sex ratios among couples. All datasets reveal a strong heterogeneity (some couples produce more boys, other more girls), with asymmetry between genders (more couples tend to produce larger numbers of girls than couples who produce larger numbers of boys). A log-Gamma function was fitted to the empirical data. Results show a wide variety of situations, from couples who produce twice as many girls than boys, to couples who produce twice as many boys than girls. Results are discussed in light of underlying biological diversity, and for their theoretical and practical implications.