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The Twin Instrument

Author

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  • Bhalotra, Sonia R.

    () (University of Essex)

  • Clarke, Damian

    () (Universidad de Santiago de Chile)

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

  • Bhalotra, Sonia R. & Clarke, Damian, 2016. "The Twin Instrument," IZA Discussion Papers 10405, Institute for the Study of Labor (IZA).
  • Handle: RePEc:iza:izadps:dp10405
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    References listed on IDEAS

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    1. Sandra E. Black & Paul J. Devereux & Kjell G. Salvanes, 2005. "The More the Merrier? The Effect of Family Size and Birth Order on Children's Education," The Quarterly Journal of Economics, Oxford University Press, vol. 120(2), pages 669-700.
    2. Mark R. Rosenzweig & Junsen Zhang, 2009. "Do Population Control Policies Induce More Human Capital Investment? Twins, Birth Weight and China's "One-Child" Policy," Review of Economic Studies, Oxford University Press, vol. 76(3), pages 1149-1174.
    3. Hongbin Li & Junsen Zhang & Yi Zhu, 2008. "The quantity-Quality trade-Off of children In a developing country: Identification using chinese twins," Demography, Springer;Population Association of America (PAA), vol. 45(1), pages 223-243, February.
    4. Emla Fitzsimons & Bansi Malde, 2014. "Empirically probing the quantity–quality model," Journal of Population Economics, Springer;European Society for Population Economics, vol. 27(1), pages 33-68, January.
    5. Vladimir Ponczek & Andre Portela Souza, 2012. "New Evidence of the Causal Effect of Family Size on Child Quality in a Developing Country," Journal of Human Resources, University of Wisconsin Press, vol. 47(1), pages 64-106.
    6. Timothy G. Conley & Christian B. Hansen & Peter E. Rossi, 2012. "Plausibly Exogenous," The Review of Economics and Statistics, MIT Press, vol. 94(1), pages 260-272, February.
    7. Julio Cáceres-Delpiano, 2006. "The Impacts of Family Size on Investment in Child Quality," Journal of Human Resources, University of Wisconsin Press, vol. 41(4).
    8. David S. Lee, 2009. "Training, Wages, and Sample Selection: Estimating Sharp Bounds on Treatment Effects," Review of Economic Studies, Oxford University Press, vol. 76(3), pages 1071-1102.
    9. Joshua Angrist & Victor Lavy & Analia Schlosser, 2010. "Multiple Experiments for the Causal Link between the Quantity and Quality of Children," Journal of Labor Economics, University of Chicago Press, vol. 28(4), pages 773-824, October.
    10. Damian Clarke, 2014. "PLAUSEXOG: Stata module to implement Conley et al's plausibly exogenous bounds," Statistical Software Components S457832, Boston College Department of Economics, revised 29 Sep 2017.
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    Cited by:

    1. Akresh, Richard & Bhalotra, Sonia R. & Leone, Marinella & Osili, Una O., 2017. "First and Second Generation Impacts of the Biafran War," IZA Discussion Papers 10938, Institute for the Study of Labor (IZA).
    2. 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.
    3. 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.
    4. 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.
    5. Mehtabul Azam & Chan Hang Saing, 2017. "Is there really a trade-off? Family Size and Investment in Child Quality in India," Economics Working Paper Series 1712, Oklahoma State University, Department of Economics and Legal Studies in Business.
    6. 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.
    7. Clarke, Damian & Matta, Benjamín, 2017. "Practical Considerations for Questionable IVs," MPRA Paper 79991, University Library of Munich, Germany.
    8. 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.

    More about this item

    Keywords

    twins; fertility; maternal health; miscarriage; bounds; quantity-quality trade-off; parental investment;

    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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