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The Twin Instrument

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  • Sonia Bhalotra
  • Damian Clarke

Abstract

Twin births are often construed as a natural experiment in the social and natural sciences on the premise that the occurrence of twins is quasi-random. We present new population-level evidence that challenges this premise. Using individual data for more than 18 million births (more than 500,000 of which are twins) in 72 countries, we demonstrate that indicators of the mother's health and health-related behaviours and exposures are systematically positively associated with the probability of a twin birth. The estimated associations are sizeable, evident in richer and poorer countries, and evident even in a sample of women who do not use IVF. The positive selection of women into twinning implies that estimates of impacts of fertility on parental investments and on women's labour supply that use twin births to instrument fertility will tend to be downward biased. This is pertinent given the emerging consensus that these relationships are weak. Using two large samples, one for developing countries and one for the United States, and focusing upon twin-instrumented estimates of the quantity-quality trade-off, we demonstrate the nature of the bias and estimate bounds on the true parameter.

Suggested Citation

  • Sonia Bhalotra & Damian Clarke, 2016. "The Twin Instrument," CSAE Working Paper Series 2016-38, Centre for the Study of African Economies, University of Oxford.
  • Handle: RePEc:csa:wpaper:2016-38
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    References listed on IDEAS

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    Cited by:

    1. Tabea Bucher-Koenen & Helmut Farbmacher & Raphael Guber & Johan Vikström, 2020. "Double Trouble: The Burden of Child-rearing and Working on Maternal Mortality," Demography, Springer;Population Association of America (PAA), vol. 57(2), pages 559-576, April.
    2. Richard Akresh & Sonia Bhalotra & Marinella Leone & Una Osili, 2017. "Hunger Games: First and Second Generation Impacts of the Biafran War," HiCN Working Papers 254, Households in Conflict Network.
    3. PONGOU Roland & SHAPIRO David & TENIKUE Michel, 2018. "Missing Twins: Fetal Origins, Institutions, and Twin-singleton Mortality Convergence," LISER Working Paper Series 2018-04, LISER.
    4. Sahawal Alidou & Marijke Verpoorten, 2019. "Family size and schooling in sub-Saharan Africa: testing the quantity-quality trade-off," Journal of Population Economics, Springer;European Society for Population Economics, vol. 32(4), pages 1353-1399, October.
    5. Erika Raquel Badillo & Lina Cardona-Sosa & Carlos Medina & Leonardo Fabio Morales & Christian Posso, 2019. "Twin instrument, fertility and women’s labor force participation: evidence from Colombian low-income families," Borradores de Economia 1071, Banco de la Republica de Colombia.
    6. Richard Akresh & Sonia Bhalotra & Marinella Leone & Una O. Osili, 2017. "First and Second Generation Impacts of the Biafran War," NBER Working Papers 23721, National Bureau of Economic Research, Inc.
    7. Aaronson, Daniel & Dehejia, Rajeev & Jordon, Andrew & Pop-Eleches, Cristian & Samii, Cyrus & Schultze, Karl, 2017. "The Effect of Fertility on Mothers’ Labor Supply over the Last Two Centuries," MPRA Paper 76768, University Library of Munich, Germany.
    8. Azam Mehtabul & Hang Saing Chan, 2018. "Is There Really a Trade-Off? Family Size and Investment in Child Quality in India," The B.E. Journal of Economic Analysis & Policy, De Gruyter, vol. 18(1), pages 1-12, January.
    9. Seongsoo Choi & Riley Taiji & Manting Chen & Christiaan Monden, 2020. "Cohort Trends in the Association Between Sibship Size and Educational Attainment in 26 Low-Fertility Countries," Demography, Springer;Population Association of America (PAA), vol. 57(3), pages 1035-1062, June.
    10. Ea Hoppe Blaabæk & Mads Meier Jæger & Joseph Molitoris, 2020. "Family Size and Educational Attainment: Cousins, Contexts, and Compensation," European Journal of Population, Springer;European Association for Population Studies, vol. 36(3), pages 575-600, July.
    11. Damian Clarke & Benjamín Matta, 2018. "Practical considerations for questionable IVs," Stata Journal, StataCorp LP, vol. 18(3), pages 663-691, September.
    12. Marie Baguet & Christelle Dumas, 2019. "How does birth weight affect health and human capital? A short‐ and long‐term evaluation," Health Economics, John Wiley & Sons, Ltd., vol. 28(5), pages 597-617, May.
    13. Anne (A.C.) Gielen & Esmee Zwiers, 2018. "Biology and the gender gap in educational performance - The role of prenatal testosterone in test scores," Tinbergen Institute Discussion Papers 18-086/V, Tinbergen Institute.
    14. Climent Quintana-Domeque & Pedro Rodenas-Serrano, 2014. "Terrorism and Human Capital at Birth: Bomb Casualties and Birth Outcomes in Spain," Working Papers 2014-020, Human Capital and Economic Opportunity Working Group.
    15. Wei Fan & Catherine Porter, 2020. "Reinforcement or compensation? Parental responses to children’s revealed human capital levels," Journal of Population Economics, Springer;European Society for Population Economics, vol. 33(1), pages 233-270, January.
    16. Fernihough, Alan, 2017. "Less is More? The child quantity-quality trade-off in early 20th century England and Wales," QUCEH Working Paper Series 2017-07, Queen's University Belfast, Queen's University Centre for Economic History.
    17. Damian Clarke, 2018. "Children And Their Parents: A Review Of Fertility And Causality," Journal of Economic Surveys, Wiley Blackwell, vol. 32(2), pages 518-540, April.
    18. Liang, Yun & Gibson, John, 2018. "Do siblings take your food away? Using China's one-child policy to test for child quantity-quality trade-offs," China Economic Review, Elsevier, vol. 48(C), pages 14-26.
    19. Baguet, Marie & Dumas, Christelle, 2015. "Birth weight and long-term outcomes in a developing country," FSES Working Papers 465, Faculty of Economics and Social Sciences, University of Freiburg/Fribourg Switzerland.

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    More about this item

    Keywords

    Twins; fertility; maternal health; miscarriage; quantity-quality trade-off; parental investment; bounds;
    All these keywords.

    JEL classification:

    • J12 - Labor and Demographic Economics - - Demographic Economics - - - Marriage; Marital Dissolution; Family Structure
    • J13 - Labor and Demographic Economics - - Demographic Economics - - - Fertility; Family Planning; Child Care; Children; Youth
    • C13 - Mathematical and Quantitative Methods - - Econometric and Statistical Methods and Methodology: General - - - Estimation: General
    • D13 - Microeconomics - - Household Behavior - - - Household Production and Intrahouse Allocation
    • I12 - Health, Education, and Welfare - - Health - - - Health Behavior

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