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The Twin Instrument

Listed author(s):
  • Bhalotra, Sonia R.

    ()

    (University of Essex)

  • Clarke, Damian

    ()

    (Universidad de Santiago de Chile)

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.

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File URL: http://ftp.iza.org/dp10405.pdf
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Paper provided by Institute for the Study of Labor (IZA) in its series IZA Discussion Papers with number 10405.

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Length: 107 pages
Date of creation: Dec 2016
Handle: RePEc:iza:izadps:dp10405
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  1. 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.
  2. 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.
  3. 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.
  4. 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.
  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. 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.
  7. 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.
  8. 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 24 Jun 2017.
  9. 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).
  10. 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.
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