, Volume 54, Issue 1, pp 71–91 | Cite as

Is the Association Between Education and Fertility Postponement Causal? The Role of Family Background Factors

  • Felix C. Tropf
  • Jornt J. Mandemakers


A large body of literature has demonstrated a positive relationship between education and age at first birth. However, this relationship may be partly spurious because of family background factors that cannot be controlled for in most research designs. We investigate the extent to which education is causally related to later age at first birth in a large sample of female twins from the United Kingdom (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 one-half year later age at first birth in ordinary least squares (OLS) models. This estimate reduced to only a 1.5-month later age at first birth for the within–identical twin model controlling for all shared family background factors (genetic and family environmental). Biometric analyses reveal that it is mainly influences of the family environment—not genetic factors—that cause spurious associations between education and age at first birth. Last, using data from the Office for National Statistics, we demonstrate that only 1.9 months of the 2.74 years of fertility postponement for birth cohorts 1944–1967 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.


Fertility postponement Education Fixed effects Twins United Kingdom 



The research leading to these results was funded by the Dutch Science Foundation (VIDI Innovation Grant 452-10-012 to M. Mills), the European Research Council (ERC) Consolidator Grant SOCIOGENOME (615603,, and Economic & Social Research Council (ESRC) UK, National Centre for Research Methods (NCRM) SOCGEN grant ( The TwinsUK study was funded by the Wellcome Trust, European Community’s Seventh Framework Programme (FP7/2007-2013). The study also received support from the National Institute for Health Research (NIHR)–funded BioResource, Clinical Research Facility and Biomedical Research Centre based at Guy’s and St. Thomas’ NHS Foundation Trust in partnership with King’s College London. The authors wish to express their gratitude to Hans-Peter Kohler and colleagues who generously provided their R-scripts to estimate the ACE-beta model. The authors gratefully acknowledge Tomas Sobotka for information and advice about data on age at first birth for the UK. We wish to thank Melinda Mills, Patrick Praeg, Tomas Sobotka, Renske Verweij, Nicola Barban, Cecilia Potente, Mariana Bonnouvrier, and Noah Carl for useful comments on earlier versions of the article. We wish to thank reviewers and editors, as well as all participants from the TwinsUK.

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Copyright information

© Population Association of America 2016

Authors and Affiliations

  1. 1.Department of Sociology/Nuffield CollegeUniversity of OxfordOxfordUK
  2. 2.University of Groningen/ICSGroningenThe Netherlands
  3. 3.Department of Social SciencesWageningen UniversityWageningenThe Netherlands

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