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Analysis of Twins

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  • Bhalotra, Sonia R.

    (University of Warwick)

  • Clarke, Damian

    (University of Chile)

Abstract

The occurrence of twin births has been widely used as a natural experiment. With a focus upon the use of twin births for identification of causal effects in economics, this chapter provides a critical review of methods and results.

Suggested Citation

  • Bhalotra, Sonia R. & Clarke, Damian, 2022. "Analysis of Twins," IZA Discussion Papers 15609, Institute of Labor Economics (IZA).
    • Handle: RePEc:iza:izadps:dp15609
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    1. Heather Royer, 2009. "Separated at Girth: US Twin Estimates of the Effects of Birth Weight," American Economic Journal: Applied Economics, American Economic Association, vol. 1(1), pages 49-85, January.
    2. Douglas Almond & Bhashkar Mazumder, 2013. "Fetal Origins and Parental Responses," Annual Review of Economics, Annual Reviews, vol. 5(1), pages 37-56, May.
    3. Sandewall, Örjan & Cesarini, David & Johannesson, Magnus, 2014. "The co-twin methodology and returns to schooling — testing a critical assumption," Labour Economics, Elsevier, vol. 26(C), pages 1-10.
    4. Petter Lundborg & Anton Nilsson & Dan-Olof Rooth, 2016. "The health-schooling relationship: evidence from Swedish twins," Journal of Population Economics, Springer;European Society for Population Economics, vol. 29(4), pages 1191-1215, October.
    5. Kenneth I. Wolpin & Mark R. Rosenzweig, 2000. "Natural "Natural Experiments" in Economics," Journal of Economic Literature, American Economic Association, vol. 38(4), pages 827-874, December.
    6. Neumark, David, 1999. "Biases in twin estimates of the return to schooling," Economics of Education Review, Elsevier, vol. 18(2), pages 143-148, April.
    7. Nils Braakmann & John Wildman, 2016. "Reconsidering the effect of family size on labour supply: the twin problems of the twin birth instrument," Journal of the Royal Statistical Society Series A, Royal Statistical Society, vol. 179(4), pages 1093-1115, October.
    8. 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, President and Fellows of Harvard College, vol. 120(2), pages 669-700.
    9. Mark R. Rosenzweig & Junsen Zhang, 2009. "Do Population Control Policies Induce More Human Capital Investment? Twins, Birth Weight and China's "One-Child" Policy," The Review of Economic Studies, Review of Economic Studies Ltd, vol. 76(3), pages 1149-1174.
    10. Behrman, Jere R. & Xiong, Yanyan & Zhang, Junsen, 2015. "Cross-sectional schooling-health associations misrepresented causal schooling effects on adult health and health-related behaviors: Evidence from the Chinese Adults Twins Survey," Social Science & Medicine, Elsevier, vol. 127(C), pages 190-197.
    11. Vikesh Amin & Jere Behrman, 2014. "Do more-schooled women have fewer children and delay childbearing? Evidence from a sample of US twins," Journal of Population Economics, Springer;European Society for Population Economics, vol. 27(1), pages 1-31, January.
    12. Braakmann, Nils & Wildman, John, 2014. "Fertility treatments and the use of twin births as an instrument for fertility," MPRA Paper 54106, University Library of Munich, Germany.
    13. Sandra E. Black & Paul J. Devereux & Kjell G. Salvanes, 2007. "From the Cradle to the Labor Market? The Effect of Birth Weight on Adult Outcomes," The Quarterly Journal of Economics, President and Fellows of Harvard College, vol. 122(1), pages 409-439.
    14. Sonia Bhalotra & Damian Clarke, 2019. "Twin Birth and Maternal Condition," The Review of Economics and Statistics, MIT Press, vol. 101(5), pages 853-864, December.
    15. Petter Lundborg, 2013. "The health returns to schooling—what can we learn from twins?," Journal of Population Economics, Springer;European Society for Population Economics, vol. 26(2), pages 673-701, April.
    16. Jere R. Behrman & Mark R. Rosenzweig, 2002. "Does Increasing Women's Schooling Raise the Schooling of the Next Generation?," American Economic Review, American Economic Association, vol. 92(1), pages 323-334, March.
    17. Miller, Paul & Mulvey, Charles & Martin, Nick, 2005. "Birth weight and schooling and earnings: estimates from a sample of twins," Economics Letters, Elsevier, vol. 86(3), pages 387-392, March.
    18. Douglas Almond & Lena Edlund & Mårten Palme, 2009. "Chernobyl's Subclinical Legacy: Prenatal Exposure to Radioactive Fallout and School Outcomes in Sweden," The Quarterly Journal of Economics, President and Fellows of Harvard College, vol. 124(4), pages 1729-1772.
    19. Henrik Cronqvist & Stephan Siegel, 2015. "The Origins of Savings Behavior," Journal of Political Economy, University of Chicago Press, vol. 123(1), pages 123-169.
    20. Behrman, Jere R & Rosenzweig, Mark R & Taubman, Paul, 1996. "College Choice and Wages: Estimates Using Data on Female Twins," The Review of Economics and Statistics, MIT Press, vol. 78(4), pages 672-685, November.
    21. Henrik Kleven & Camille Landais & Jakob Egholt Søgaard, 2019. "Children and Gender Inequality: Evidence from Denmark," American Economic Journal: Applied Economics, American Economic Association, vol. 11(4), pages 181-209, October.
    22. Åslund, Olof & Grönqvist, Hans, 2010. "Family size and child outcomes: Is there really no trade-off?," Labour Economics, Elsevier, vol. 17(1), pages 130-139, January.
    23. 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.
    24. repec:bla:econom:v:64:y:1997:i:253:p:119-36 is not listed on IDEAS
    25. Kenneth Y. Chay & Michael Greenstone, 2003. "The Impact of Air Pollution on Infant Mortality: Evidence from Geographic Variation in Pollution Shocks Induced by a Recession," The Quarterly Journal of Economics, President and Fellows of Harvard College, vol. 118(3), pages 1121-1167.
    26. Böckerman, Petri & Maczulskij, Terhi, 2016. "The Education-health Nexus: Fact and fiction," Social Science & Medicine, Elsevier, vol. 150(C), pages 112-116.
    27. Savelyev, Peter A. & Ward, Benjamin C. & Krueger, Robert F. & McGue, Matt, 2022. "Health endowments, schooling allocation in the family, and longevity: Evidence from US twins," Journal of Health Economics, Elsevier, vol. 81(C).
    28. Behrman, Jere R & Taubman, Paul, 1976. "Intergenerational Transmission of Income and Wealth," American Economic Review, American Economic Association, vol. 66(2), pages 436-440, May.
    29. Berniell, Inés & Berniell, Lucila & Mata, Dolores de la & Edo, María & Marchionni, Mariana, 2021. "Gender gaps in labor informality: The motherhood effect," Journal of Development Economics, Elsevier, vol. 150(C).
    30. Bound, John & Solon, Gary, 1999. "Double trouble: on the value of twins-based estimation of the return to schooling," Economics of Education Review, Elsevier, vol. 18(2), pages 169-182, April.
    31. Rouse, Cecilia Elena, 1999. "Further estimates of the economic return to schooling from a new sample of twins," Economics of Education Review, Elsevier, vol. 18(2), pages 149-157, April.
    32. Rosenzweig, Mark R & Wolpin, Kenneth I, 1980. "Testing the Quantity-Quality Fertility Model: The Use of Twins as a Natural Experiment," Econometrica, Econometric Society, vol. 48(1), pages 227-240, January.
    33. Junjian Yi & James J. Heckman & Junsen Zhang & Gabriella Conti, 2015. "Early Health Shocks, Intra†household Resource Allocation and Child Outcomes," Economic Journal, Royal Economic Society, vol. 125(588), pages 347-371, November.
    34. Philip Oreopoulos & Mark Stabile & Randy Walld & Leslie L. Roos, 2008. "Short-, Medium-, and Long-Term Consequences of Poor Infant Health: An Analysis Using Siblings and Twins," Journal of Human Resources, University of Wisconsin Press, vol. 43(1).
    35. David Figlio & Jonathan Guryan & Krzysztof Karbownik & Jeffrey Roth, 2014. "The Effects of Poor Neonatal Health on Children's Cognitive Development," American Economic Review, American Economic Association, vol. 104(12), pages 3921-3955, December.
    36. Gunnar Isacsson, 2004. "Estimating the economic return to educational levels using data on twins," Journal of Applied Econometrics, John Wiley & Sons, Ltd., vol. 19(1), pages 99-119.
    37. 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.
    38. Mogstad, M. & Wiswall, M., 2012. "Instrumental variables estimation with partially missing instruments," Economics Letters, Elsevier, vol. 114(2), pages 186-189.
    39. Amin, Vikesh & Lundborg, Petter & Rooth, Dan-Olof, 2011. "Mothers Do Matter: New Evidence on the Effect of Parents' Schooling on Children's Schooling Using Swedish Twin Data," IZA Discussion Papers 5946, Institute of Labor Economics (IZA).
    40. Bhalotra, Sonia & Clarke, Damian & Mühlrad, Hanna & Palme, Mårten, 2021. "Health and Labor Market Impacts of Twin Birth : Evidence from a Swedish IVF Policy Mandate," The Warwick Economics Research Paper Series (TWERPS) 1391, University of Warwick, Department of Economics.
    41. Magne Mogstad & Matthew Wiswall, 2016. "Testing the quantity–quality model of fertility: Estimation using unrestricted family size models," Quantitative Economics, Econometric Society, vol. 7(1), pages 157-192, March.
    42. Hanushek, Eric A, 1992. "The Trade-Off between Child Quantity and Quality," Journal of Political Economy, University of Chicago Press, vol. 100(1), pages 84-117, February.
    43. Dinand Webbink & Pierre Koning & Sunčica Vujić & Nicholas G. Martin, 2013. "Why Are Criminals Less Educated than Non-Criminals? Evidence from a Cohort of Young Australian Twins," The Journal of Law, Economics, and Organization, Oxford University Press, vol. 29(1), pages 115-144, February.
    44. Petter Lundborg & Erik Plug & Astrid Würtz Rasmussen, 2017. "Can Women Have Children and a Career? IV Evidence from IVF Treatments," American Economic Review, American Economic Association, vol. 107(6), pages 1611-1637, June.
    45. Conley, Dalton & Strully, Kate W. & Bennett, Neil G., 2006. "Twin differences in birth weight: The effects of genotype and prenatal environment on neonatal and post-neonatal mortality," Economics & Human Biology, Elsevier, vol. 4(2), pages 151-183, June.
    46. Douglas Almond & Kenneth Y. Chay & David S. Lee, 2005. "The Costs of Low Birth Weight," The Quarterly Journal of Economics, President and Fellows of Harvard College, vol. 120(3), pages 1031-1083.
    47. Bronars, Stephen G & Grogger, Jeff, 1994. "The Economic Consequences of Unwed Motherhood: Using Twin Births as a Natural Experiment," American Economic Review, American Economic Association, vol. 84(5), pages 1141-1156, December.
    48. Mary A. Silles, 2016. "The impact of children on women’s labour supply and earnings in the UK: evidence using twin births," Oxford Economic Papers, Oxford University Press, vol. 68(1), pages 197-216.
    49. Meltem Dayioğlu & Murat G. Kirdar & Aysit Tansel, 2009. "Impact of Sibship Size, Birth Order and Sex Composition on School Enrolment in Urban Turkey," Oxford Bulletin of Economics and Statistics, Department of Economics, University of Oxford, vol. 71(3), pages 399-426, June.
    50. Angrist, Joshua D & Evans, William N, 1998. "Children and Their Parents' Labor Supply: Evidence from Exogenous Variation in Family Size," American Economic Review, American Economic Association, vol. 88(3), pages 450-477, June.
    51. Joyce P. Jacobsen & James Wishart Pearce III & Joshua L. Rosenbloom, 1999. "The Effects of Childbearing on Married Women's Labor Supply and Earnings: Using Twin Births as a Natural Experiment," Journal of Human Resources, University of Wisconsin Press, vol. 34(3), pages 449-474.
    52. Miller, Paul W & Mulvey, Charles & Martin, Nick, 1995. "What Do Twins Studies Reveal about the Economic Returns to Education? A Comparison of Australian and U.S. Findings," American Economic Review, American Economic Association, vol. 85(3), pages 586-599, June.
    53. Jere Behrman & Hans-Peter Kohler & Vibeke Jensen & Dorthe Pedersen & Inge Petersen & Paul Bingley & Kaare Christensen, 2011. "Does More Schooling Reduce Hospitalization and Delay Mortality? New Evidence Based on Danish Twins," Demography, Springer;Population Association of America (PAA), vol. 48(4), pages 1347-1375, November.
    54. Behrman, Jere R & Taubman, Paul, 1989. "Is Schooling "Mostly in the Genes"? Nature-N urture Decomposition Using Data on Relatives," Journal of Political Economy, University of Chicago Press, vol. 97(6), pages 1425-1446, December.
    55. Zhang, Junchao, 2017. "A dilemma of fertility and female labor supply: Identification using Taiwanese twins," China Economic Review, Elsevier, vol. 43(C), pages 47-63.
    56. Orley Ashenfelter & Cecilia Rouse, 1998. "Income, Schooling, and Ability: Evidence from a New Sample of Identical Twins," The Quarterly Journal of Economics, President and Fellows of Harvard College, vol. 113(1), pages 253-284.
    57. James P. Vere, 2011. "Fertility and parents' labour supply: new evidence from US census data," Oxford Economic Papers, Oxford University Press, vol. 63(2), pages 211-231, April.
    58. Mark E. McGovern, 2019. "How much does birth weight matter for child health in developing countries? Estimates from siblings and twins," Health Economics, John Wiley & Sons, Ltd., vol. 28(1), pages 3-22, January.
    59. Amin, Vikesh & Behrman, Jere R. & Spector, Tim D., 2013. "Does more schooling improve health outcomes and health related behaviors? Evidence from U.K. twins," Economics of Education Review, Elsevier, vol. 35(C), pages 134-148.
    60. Dinand Webbink & Nicholas Martin & Peter Visscher, 2011. "Does teenage childbearing reduce investment in human capital?," Journal of Population Economics, Springer;European Society for Population Economics, vol. 24(2), pages 701-730, April.
    61. Martin Kolk, 2015. "The causal effect of an additional sibling on completed fertility: An estimation of intergenerational fertility correlations by looking at siblings of twins," Demographic Research, Max Planck Institute for Demographic Research, Rostock, Germany, vol. 32(51), pages 1409-1420.
    62. Prashant Bharadwaj & Juan Pedro Eberhard & Christopher A. Neilson, 2018. "Health at Birth, Parental Investments, and Academic Outcomes," Journal of Labor Economics, University of Chicago Press, vol. 36(2), pages 349-394.
    63. Amin, Vikesh & Behrman, Jere R. & Kohler, Hans-Peter, 2015. "Schooling has smaller or insignificant effects on adult health in the US than suggested by cross-sectional associations: New estimates using relatively large samples of identical twins," Social Science & Medicine, Elsevier, vol. 127(C), pages 181-189.
    64. Jere R. Behrman & Mark R. Rosenzweig, 2004. "Returns to Birthweight," The Review of Economics and Statistics, MIT Press, vol. 86(2), pages 586-601, May.
    65. Miller, Paul & Mulvey, Charles & Martin, Nick, 2006. "The return to schooling: Estimates from a sample of young Australian twins," Labour Economics, Elsevier, vol. 13(5), pages 571-587, October.
    66. Letícia Marteleto & Laetícia Souza, 2012. "The Changing Impact of Family Size on Adolescents’ Schooling: Assessing the Exogenous Variation in Fertility Using Twins in Brazil," Demography, Springer;Population Association of America (PAA), vol. 49(4), pages 1453-1477, November.
    67. Sandra E. Black & Paul J. Devereux & Kjell G. Salvanes, 2016. "Does Grief Transfer across Generations? Bereavements during Pregnancy and Child Outcomes," American Economic Journal: Applied Economics, American Economic Association, vol. 8(1), pages 193-223, January.
    68. Behrman, Jere R. & Rosenzweig, Mark R., 1999. ""Ability" biases in schooling returns and twins: a test and new estimates," Economics of Education Review, Elsevier, vol. 18(2), pages 159-167, April.
    69. Martin Eckhoff Andresen & Emily Nix, 2022. "What Causes the Child Penalty? Evidence from Adopting and Same-Sex Couples," Journal of Labor Economics, University of Chicago Press, vol. 40(4), pages 971-1004.
    70. Ashenfelter, Orley & Krueger, Alan B, 1994. "Estimates of the Economic Returns to Schooling from a New Sample of Twins," American Economic Review, American Economic Association, vol. 84(5), pages 1157-1173, December.
    71. repec:ucn:wpaper:10197/317 is not listed on IDEAS
    72. Dalton Conley & Kate Strully & Neil G. Bennett, 2003. "A Pound of Flesh or Just Proxy? Using Twin Differences to Estimate the Effect of Birth Weight on Life Chances," NBER Working Papers 9901, National Bureau of Economic Research, Inc.
    73. Behrman, Jere R & Rosenzweig, Mark R & Taubman, Paul, 1994. "Endowments and the Allocation of Schooling in the Family and in the Marriage Market: The Twins Experiment," Journal of Political Economy, University of Chicago Press, vol. 102(6), pages 1131-1174, December.
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    More about this item

    Keywords

    fertility; birth spacing; child development; women's labour market outcomes; identification; twins; child penalty;
    All these keywords.

    JEL classification:

    • D10 - Microeconomics - - Household Behavior - - - General
    • I26 - Health, Education, and Welfare - - Education - - - Returns to Education
    • J13 - Labor and Demographic Economics - - Demographic Economics - - - Fertility; Family Planning; Child Care; Children; Youth
    • J24 - Labor and Demographic Economics - - Demand and Supply of Labor - - - Human Capital; Skills; Occupational Choice; Labor Productivity

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