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Older and Wiser? Birth Order and IQ of Young Men


  • Black, Sandra E.

    () (University of Texas at Austin)

  • Devereux, Paul J.

    () (University College Dublin)

  • Salvanes, Kjell G.

    () (Norwegian School of Economics)


While recent research finds strong evidence that birth order affects children’s outcomes such as education and earnings, the evidence on the effects of birth order on IQ is decidedly mixed. This paper uses a large dataset on the population of Norway that allows us to precisely measure birth order effects on IQ using both cross-sectional and within-family methods. Importantly, irrespective of method, we find a strong and significant effect of birth order on IQ, and our results suggest that earlier born children have higher IQs. Our preferred estimates suggest differences between first-borns and second-borns of about one fifth of a standard deviation or approximately 3 IQ points. Despite these large average effects, birth order only explains about 3% of the within-family variance of IQ. When we control for birth endowments, the estimated birth order effects increase. Thus, our analysis suggests that birth order effects are not biologically determined. Also, there is no evidence that birth order effects occur because later-born children are more affected by family breakdown.

Suggested Citation

  • Black, Sandra E. & Devereux, Paul J. & Salvanes, Kjell G., 2007. "Older and Wiser? Birth Order and IQ of Young Men," IZA Discussion Papers 3007, Institute for the Study of Labor (IZA).
  • Handle: RePEc:iza:izadps:dp3007

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    References listed on IDEAS

    1. Alison Booth & Hiau Kee, 2009. "Birth order matters: the effect of family size and birth order on educational attainment," Journal of Population Economics, Springer;European Society for Population Economics, vol. 22(2), pages 367-397, April.
    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. 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, Oxford University Press, vol. 122(1), pages 409-439.
    4. 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.
    5. repec:ucn:wpaper:10197/317 is not listed on IDEAS
    6. Behrman, Jere R & Taubman, Paul, 1986. "Birth Order, Schooling, and Earnings," Journal of Labor Economics, University of Chicago Press, vol. 4(3), pages 121-145, July.
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    More about this item


    birth order; IQ;

    JEL classification:

    • I2 - Health, Education, and Welfare - - Education
    • J1 - Labor and Demographic Economics - - Demographic Economics

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