Cognitive ability and fertility among Swedish men born 1951–1967: evidence from military conscription registers

Abstract

We examine the relationship between cognitive ability and childbearing patterns in contemporary Sweden using administrative register data. The topic has a long history in the social sciences and has been the topic of a large number of studies, many reporting a negative gradient between intelligence and fertility. We link fertility histories to military conscription tests with intelligence scores for all Swedish men born 1951-1967. We find a positive relationship between intelligence scores and fertility, and this pattern is consistent across the cohorts we study. The relationship is most pronounced for the transition to a first child, and men with the lowest categories of IQ scores have the fewest children. Using fixed effects models, we additionally control for all factors that are shared by siblings, and after such adjustments, we find a stronger positive relationship between IQ and fertility. Furthermore, we find a positive gradient within groups at different levels of education. Compositional differences of this kind are therefore not responsible for the positive gradient we observe-instead, the relationship is even stronger after controlling for both educational careers and parental background factors. In our models where we compare brothers to one another, we find that, relative to men with IQ 100, the group with the lowest category of cognitive ability have 0.56 fewer children, and men with the highest category have 0.09 more children.

Do income and marriage mediate the relationship between cognitive ability and fertility? Data from Swedish taxation and conscriptions registers for men born 1951-1967

“…Overall, our results indicate that the primary reason that we observe low fertility among men with lower cognitive ability is because of their failure to attract a partner for stable unions for childbearing. In addition to confirming previous findings on cognitive ability and fertility in Sweden (Kolk and Barclay 2019), the findings of this study provide evidence for the importance of partnership formation, as well as showing that the intelligence-fertility association persists even after taking cumulative income into account.…”

“…In other words, for two brothers with similar income (and a shared social background), on average the brother with higher cognitive ability has more children. Previous research has shown that high and low cognitive ability is associated with the specific number of children of men in Sweden (Kolk and Barclay 2019). In particular -as highlighted in our literature review -it is plausible that much of the lower fertility of men with higher cognitive ability is affected by a reduced probability of finding a partner for childbearing.…”

“…We define our population as all Swedish-born men of those cohorts alive until the end of their reproductive ages. Kolk and Barclay (2019) used a similar dataset to study the overall relationship between cognitive ability and fertility. In the study, they provide further information on how conscription tests were designed and validated.…”

“…Throughout the 20 th -century researchers variously reported positive and negative gradients for the fertility and cognitive ability, though in the second half of the 20 th -century researchers increasingly observed negative gradients where men, but particularly women, with lower cognitive ability had more children. A recent study using Swedish military conscription data, a data source of unusually high quality in regards to representativeness and quality of cognitive ability measurement, researchers found a clear positive association between cognitive ability and fertility for men (Kolk and 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.…”

The influence of health in early adulthood on male fertility

“…This is particularly true in a Scandinavian context in which more socioeconomically successful men have higher fertility (e.g. Jalovaara et al, 2018;Kolk and Barclay, 2019;Kolk, 2019). While the physiological mechanisms linking our anthropometric measures to fecundity may be universal, it is important to emphasise that the link between BMI, physical fitness, and height to socioeconomic attainment, and particularly physical attractiveness, have been shown to be socioculturally contingent (Pisanski and Feinberg, 2013).…”