Academic journal article Demographic Research

Sex Ratios at Sexual Maturity and Longevity: Evidence from Swedish Register Data

Academic journal article Demographic Research

Sex Ratios at Sexual Maturity and Longevity: Evidence from Swedish Register Data

Article excerpt

Abstract

BACKGROUND

This study tests the recently proposed hypothesis that the contextual sex ratio at sexual maturity is related to longevity. Previous empirical research in the United States has shown that a higher proportion of males at the age of sexual maturity increases the risk of mortality for males both before and after the age of 65.

METHODS

I use Swedish administrative register data, linking the 1960 census to individual-level mortality data over the period 1960 to 2007. I calculate the sex ratio at two geographic levels, municipalities and parishes. Two different specifications of the sex ratio are calculated: males aged 18 to 27 over females aged 15 to 24, and males aged 18 to 22 over females aged 16 to 20. I conduct piece-wise constant survival analyses over the period from 1960 to 2007 to analyze the risk of mortality before age 65. I run separate analyses for males and females, using cohorts born in 1941 and 1942.

RESULTS

For males, the results generally show that for both males and females a higher proportion of males was associated with a lower relative risk of mortality before age 65. The results were not statistically significant.

CONCLUSIONS

The lack of a consistent statistically significant association for either males or females, and the trend for males being in the opposite direction of what was hypothesized, suggests that support for the hypothesis in Sweden is very weak.

1. Introduction

While previous research has indicated that imbalances in the human sex ratio can influ- ence patterns of marriage and divorce, fertility behaviour, and labour supply (Svarer 2007; Lloyd and South 1996; Angrist 2002), very little research has addressed the relationship between sex ratios and health. A small handful of studies have examined whether gender imbalances in the workplace are associated with morbidity and differences in sickness absenteeism rates for males and females, but the evidence is mixed (Bryngelson, Hertz- man, and Fritzell 2011; Mastekaasa 2005; Hensing and Alexanderson 2004; Svedberg et al. 2009). Even less research has been conducted on the relationship between sex ratios and mortality risk. A study published recently by Jin et al. (2010) was the first to pro- pose the hypothesis that imbalances in the contextual sex ratio at sexual maturity may be related to longevity. They found that a higher proportion of males in the local context, defined as schools and U.S. states, was associated with an increased risk of mortality for males, though not for females, both before and after the age of 65. The current study will attempt to replicate these analyses as closely as possible using Swedish administra- tive register data, investigating mortality before age 65. Jin et al. (2010) proposed three potential mechanisms by which such a relationship might operate. The first was that im- balances in the sex ratio may lead to delays in marriage, and that individuals would thus be less likely to gain from the cumulative health benefits associated with marriage. Sec- ondly, imbalances in the sex ratio might mean that individuals have to settle for a partner of a lower quality, meaning that even conditional upon entry into a long-term partnership, the cumulative benefits would be lower for members of the supernumerary sex. Finally, imbalances in the sex ratio should be related to higher levels of competition for sexual partners, and the psychosocial stress associated with this elevated level of competition at a relatively sensitive age might have a long-term impact upon health.

The study performed by Jin et al. (2010) used two different datasets. The first was the Wisconsin Longitudinal Study (WLS), which collected data on one-third of all high school graduates in Wisconsin in 1957. Jin et al. (2010) were able to compute the sex ratio for the graduating class of each high school that the individuals within their sample attended. They subsequently estimated a Cox proportional hazards model, specifying shared frailty for schools, and followed the members of their sample until 2004. …

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