Education, fertility postponement and causality: the role of family background factors

Felix C. Tropf, University of Oxford
Jornt Mandemakers, Wageningen University

A large body of literature demonstrates a positive relationship between education and age at first birth. However, this relationship may in part be spurious due to family background factors that cannot be controlled for in most research designs. We investigate to what extend higher education is causally related to later age at first birth timing in a large sample of female twins from the UK (N=2,752). We present novel estimates using within-identical twin and biometric models. Our findings show that one year of additional schooling is associated with about half a year later age at first birth in standard models. This reduced to only 1.5 months for the within-identical twin model that control for all shared family background factors (genetic and family environmental). Biometric analyses reveal that mainly influences of the family environment – not genetic factors – cause spurious associations between education and age at first birth. Lastly, we demonstrate using data from the Office for National Statistics that only 1.9 months of the 2.4 years of fertility postponement for birth cohorts 1944-1969 could be attributed to educational expansion based on these estimates. We conclude that (the rise in) educational attainment alone cannot explain differences in fertility timing (between cohorts).