Socioeconomic status and sex ratios at birth in Sweden : No evidence for a Trivers-Willard effect for a wide range of status indicators

Abstract

Objectives<br /><br />This study examines if there exists a positive association between socioeconomic status and the proportion of male births in humans, as proposed by Trivers and Willard in 1973, using individual-level data drawn from the complete population of Sweden.<br /><br />Methods<br /><br />We examine more than 3,000,000 births between 1960 and 2007 using administrative register data with comprehensive information on various dimensions of socioeconomic status. We use six different operationalizations of socioeconomic status, including earnings, post-transfer income (including government allowances), wealth, parental wealth, educational level, and occupational class. We apply regression models that compare both changes in status for the same woman over time and differences in status across different women. We also measure socioeconomic status both at the year of child birth and the year of conception.<br /><br />Results<br /><br />Our results show the absence of any relationship between socioeconomic status and sex ratios, using a large number of different operationalizations of status.<br /><br />Conclusions<br /><br />We conclude that no substantive relationship between socioeconomic status and sex ratios exists for the population and period of our study.