How does variance in fertility change over the demographic transition?

Daniel Hruschka, Oskar Burger

Research output: Contribution to journalArticlepeer-review

18 Scopus citations


Most work on the human fertility transition has focused on declines in mean fertility. However, understanding changes in the variance of reproductive outcomes can be equally important for evolutionary questions about the heritability of fertility, individual determinants of fertility and changing patterns of reproductive skew. Here, we document how variance in completed fertility among women (45-49 years) differs across 200 surveys in 72 low- to middle-income countries where fertility transitions are currently in progress at various stages. Nearly all (91%) of samples exhibit variance consistent with a Poisson process of fertility, which places systematic, and often severe, theoretical upper bounds on the proportion of variance that can be attributed to individual differences. In contrast to the pattern of total variance, these upper bounds increase from high- to mid-fertility samples, then decline again as samples move from mid to low fertility. Notably, the lowest fertility samples often deviate from a Poisson process. This suggests that as populations move to low fertility their reproduction shifts from a rate-based process to a focus on an ideal number of children. We discuss the implications of these findings for predicting completed fertility from individual-level variables.

Original languageEnglish (US)
Article number20150155
JournalPhilosophical Transactions of the Royal Society B: Biological Sciences
Issue number1692
StatePublished - Apr 19 2016


  • Completed fertility
  • Fertility transition
  • Negative binomial
  • Poisson
  • Variance

ASJC Scopus subject areas

  • General Biochemistry, Genetics and Molecular Biology
  • General Agricultural and Biological Sciences


Dive into the research topics of 'How does variance in fertility change over the demographic transition?'. Together they form a unique fingerprint.

Cite this