This Is a Man's World? Changes in Disposable Income Predict Sex Ratio at Birth

The human sex ratio at birth (SRB) is long known to be relatively constant at around 107 boys born for every 100 girls. In recent studies evidence has been found that SRB might vary according to exposure to chemicals and socioeconomic conditions. SRB has also been declining after World War II in several industrial countries – a phenomenon that remains unexplained. Here we show that changes in disposable income are associated with at birth sex ratios in OECD countries. Positive changes in disposable income are associated with higher proportion of male infants. We apply panel regressions to OECD data that spans the years 1971 to 2011 for 35 countries and UN fertility data in an unbalanced panel. Findings not only partly explain the rises and declines in the sex ratio in OECD countries, but also first time provides evidence of the influence of economic and social forces on SRB that can even be seen in macro level analysis. This opens up radically new research directions in social sciences, where the emphasis on the biological factors has traditionally been on how biological determinants shape social life and in the interaction of the two, not on how social and economic determinants might affect biological facts such as the sex of an infant. This furthermore contributes to debates of gender equality. Our findings suggest that the equality of opportunity differs for genders as the sex ratio depends on the underlying economic conditions: men seem to be born into better economic conditions.