Sex ratios at sexual maturity and longevity: the evidence from Sweden
Kieron Barclay, Stockholm University
This study uses Swedish register data to test the recently proposed hypothesis that imbalances in the sex ratio at sexual maturity may affect longevity (Jin, Elwert, Freese and Christakis, 2010). The study, published in Demography, by Jin et al. (2010) found support for this hypothesis in the United States for males, but not for females, with a higher proportion of males decreasing longevity. I replicate part of that study using population data from the Swedish administrative registers. Sex ratios were calculated using 1960 census data, and the sample group was followed until 2007, the latest point for which data is available. Using the exact same specifications for the calculation of the sex ratio, I find no support for the hypothesis in Sweden for either males or females. I then adjusted the age ranges within which the sex ratio was calculated, to reflect differences between Sweden and the United States in terms of patterns of cohabitation and mean ages for marriage and childbearing. I calculated sex ratios for two further age ranges: males aged 18-20 and females aged 16-18; and, males aged 20-32 and females aged 18-30. The results from these analyses indicate that a higher proportion of males at sexual maturity is significantly associated with mortality risk before the age of 65 for females, but not for males. These results lend tentative support to this hypothesis, but it is possible the sex ratios calculated within geographical units of various sizes do not accurately reflect the actual environments that individuals are exposed to. Further analyses for the final version of this paper will include looking at how sex ratios are associated with mortality risk for males and females over the age of 65, and analyses using sex ratios calculated with school data.