Abstract
Despite the large body of research on educational differences in fertility, how genetic and environmental influences may contribute to educational differences in completed fertility is not well understood. This study examines the association between educational level and completed fertility in a sample of Finnish male and female twins born between 1950 and 1957 with register-based fertility follow-up until 2009. The results show that poorly educated men and highly educated women are least likely to have any children and have lower completed fertility in general. Behavioral genetics analysis suggests that the association between education and having any children in both sexes is influenced by factors shared by co-twins and that these factors are genetic rather than common environmental. No evidence of a causal pathway between education and having any children independent of these shared influences is found. These findings suggest that familial factors may play a role in the process through which educational differences in completed fertility are formed.
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Notes
The sex-specific categorization of the educational variable is based on the preceding results: the association between education and fertility was nonlinear in both sexes with these specific cut-off points of the variable scale, thus showing a threshold effect.
Tetrachoric correlation refers to correlations calculated for dichotomous variables from an underlying assumed standard normal distribution in order to estimate either covariance between co-twins across two traits (cross-twin/cross-trait covariance) or twin-pair resemblance in a trait (cross-twin/within-trait covariance).
The genetic correlation (r A) is calculated by \( {r_A}={{{{{{\operatorname{cov}}}_{{A\left( {Edu,Child} \right)}}}}} \left/ {{\left( {\sqrt{{{{{\operatorname{var}}}_{{A\left( {Edu} \right)}}}}}\times \sqrt{{{{{\operatorname{var}}}_{{A\left( {Child} \right)}}}}}} \right)}} \right.} \), where A refers to genetic factors, Edu refers to educational level, and Child refers to having any children. The common (r C) and unique (r E) environmental correlation is calculated in the same way except that C / E replaces A.
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Acknowledgments
Jessica Nisén and Karri Silventoinen wish to thank Kone Foundation for support during the course of the research. Pekka Martikainen and Jaakko Kaprio were supported by the Academy of Finland (JK by Grant 141054). The authors are grateful to the editors and reviewers of Demography for their valuable comments.
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Nisén, J., Martikainen, P., Kaprio, J. et al. Educational Differences in Completed Fertility: A Behavioral Genetic Study of Finnish Male and Female Twins. Demography 50, 1399–1420 (2013). https://doi.org/10.1007/s13524-012-0186-9
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DOI: https://doi.org/10.1007/s13524-012-0186-9