, Volume 54, Issue 1, pp 23–44 | Cite as

The Effect of Childhood Family Size on Fertility in Adulthood: New Evidence From IV Estimation

  • Sara Cools
  • Rannveig Kaldager Hart


Although fertility is positively correlated across generations, the causal effect of children’s experience with larger sibships on their own fertility in adulthood is poorly understood. With the sex composition of the two firstborn children as an instrumental variable, we estimate the effect of sibship size on adult fertility using high-quality data from Norwegian administrative registers. Our study sample is all firstborns or second-borns during the 1960s in Norwegian families with at least two children (approximately 110,000 men and 104,000 women). An additional sibling has a positive effect on male fertility, mainly causing them to have three children themselves, but has a negative effect on female fertility at the same margin. Investigation into mediators reveals that mothers of girls shift relatively less time from market to family work when an additional child is born. We speculate that this scarcity in parents’ time makes girls aware of the strains of life in large families, leading them to limit their own number of children in adulthood.


Fertility Intergenerational transmission Instrumental variables Family size 



We are grateful to Lars Dommermuth, Joshua Goldstein, Shoshana Grossbard, Hege Kitterød, Andreas Kotsadam, Øystein Kravdal, Trude Lappegård, Torkild Lyngstad, Birgitte Sande Riise, Marit Rønsen, Kjetil Telle, and Odd Vaage as well as seminar participants at PAA 2014, ESPE 2014, EPC 2014, and Department of Demography at UC Berkeley, and the Editor and referees of Demography for helpful comments. The project is part of the research activities at ESOP at the University of Oslo, in collaboration with the Ragnar Frisch Centre for Economic Research, Project 1110, both of which are supported by the Norwegian Research Council. Data made available by Statistics Norway have been essential for the research project. Hart’s work was supported by the Norwegian Research Council under Grant No. 202442/S20 and 236926.

Supplementary material

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Copyright information

© Population Association of America 2016

Authors and Affiliations

  1. 1.Institute for Social ResearchOsloNorway
  2. 2.Department of Sociology and Human GeographyUniversity of OsloOsloNorway
  3. 3.Research DepartmentStatistics NorwayOsloNorway

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