Abstract
Recent evidence suggests a positive association between fertility and cognitive ability among Swedish men. In this study we use data on 18 birth cohorts of Swedish men to examine whether and how the relationship between cognitive ability and patterns of childbearing are mediated by income, education and marriage histories. We examine whether the expected positive associations between cognitive ability and life course income can explain this positive association. We also explore the role of marriage for understanding the positive gradient between cognitive ability and fertility. To address these questions we use Swedish population administrative data that holds information on fertility histories, detailed taxation records, and data from conscription registers. We also identify siblings in order to adjust for confounding by shared family background factors. Our results show that while cognitive ability, education, income, marriage, and fertility, are all positively associated with each other, income only explains a part of the observed positive gradient between fertility and cognitive ability. We find that much of the association between cognitive ability and fertility can be explained by marriage, but that a positive association exists among both ever-married and never-married men. Both low income and low cognitive ability are strong predictors of childlessness and low fertility in our population. The results from the full population persist in the sub-sample of brothers.
Highlights
The relationship between cognitive ability and fertility has vexed researchers for over a century
In the current study we further examine relationships between cognitive ability and fertility in Sweden by addressing the following five research questions (RQ 1–5): First (RQ1), is there a positive gradient between fertility and cognitive ability even after controlling for income during the life course? Second (RQ 2), is the relationship between fertility and cognitive ability similar for men with high and low income? Third (RQ 3), do cognitive ability and income affect the propensity to marry? Fourth (RQ 4), how much of the relationship between fertility, cognitive ability, and income can be explained by high-income men more often forming stable partnerships? We examine this by studying childlessness and fertility among ever-married and never-married men
We find that the association between cognitive ability and fertility for low cognitive ability men is partly mediated by low income
Summary
The relationship between cognitive ability and fertility has vexed researchers for over a century. Throughout the 20th-century researchers variously reported positive and negative gradients for fertility and cognitive ability, though in the second half of the 20th-century re searchers increasingly observed negative gradients where men and women with lower cognitive ability had more children (where the effect was larger for women). A recent study using Swedish military conscription data, a data source of unusually high quality in terms of representativeness and quality of cognitive ability measurement, found a clear positive association between cognitive ability and fertility for men (Kolk & Barclay, 2019). In this study we use a similar dataset from Sweden, linked with high quality yearly taxation records, to examine the extent to which socioeconomic success among higher cognitive ability individuals might explain the positive fertility and cognitive ability gradient. We employ data on marriage histories to examine the extent to which marriage mediates the association, to understand the extent to which the cognitive ability and fertility gradient are explained by partnership availability or fertility preferences of men within unions
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