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An introduction to using twin births as instrumental variables for sibship size

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  • Öberg, Stefan

    () (Department of Economy and Society)

Abstract

Some families who experience a twin birth get one more child than they had intended and planned for. This is the reason why twin births are used to create instrumental variables (IVs) for the number of children in a family. In this chapter I introduce IV techniques in general and the use of twin births for IVs in particular. IVs based on parity-specific twin births can indeed, under certain circumstances, be valid and reliable. In this chapter I discuss what these circumstances are. I rely heavily on the work by Joshua Angrist and coauthors. In contrast to them I argue that it is important to recognize that IVs based on parity-specific twin births have “heterogenous treatment effects”, meaning that it is only for some families that the twin birth leads to an unintended and unplanned birth. Recognizing this highlights a few assumptions that are not always thoroughly acknowledged in previous research. We, for example, need to make assumptions about the possibility of unintended single births and the families experiencing these. It is also the case that including families that have not yet reached (or surpassed) their desired number of children when using IVs based on parity-specific twin births will lead to estimates that are biased towards zero. Most importantly we need to reduce the claims of estimating generalizable, causal effects when using twin birth instrumental variables.

Suggested Citation

  • Öberg, Stefan, 2017. "An introduction to using twin births as instrumental variables for sibship size," Göteborg Papers in Economic History 22, University of Gothenburg, Department of Economic History.
  • Handle: RePEc:hhs:gunhis:0022
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    File URL: http://hdl.handle.net/2077/52286
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    References listed on IDEAS

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    1. Bohlin, Jan, 2007. "Structural Change in the Swedish economy in the late nineteenth and early twentieth century – The role of import substitution and export demand," Göteborg Papers in Economic History 8, University of Gothenburg, Department of Economic History.
    2. Olsson, Ulf, 2013. "En värdefull berättelse Wallenbergarnas historieprojekt," Göteborg Papers in Economic History 16, University of Gothenburg, Department of Economic History.
    3. Larsson, Svante, 2005. "Globalisation, inequality and Swedish catch up in the late nineteenth century. Williamson’s real wage comparisons under scrutiny," Göteborg Papers in Economic History 2, University of Gothenburg, Department of Economic History.
    4. Bohlin, Jan, 2006. "The income distributional consequences of agrarian tariffs in Sweden on the eve of World War I," Göteborg Papers in Economic History 6, University of Gothenburg, Department of Economic History.
    5. Karlsson, Tobias, 2015. "Pushed into Unemployment, Pulled into Retirement: Facing Old Age in Gothenburg, 1923-1943," Göteborg Papers in Economic History 19, University of Gothenburg, Department of Economic History.
    6. Elmerot, Irene, 2015. "Skrivhandledning. För doktorander i ekonomisk historia vid Göteborgs universitet," Göteborg Papers in Economic History 17, University of Gothenburg, Department of Economic History.
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    More about this item

    Keywords

    instrumental variables; twins; twin births; family size; exogenous variation; causal estimation; sibship size;

    JEL classification:

    • C26 - Mathematical and Quantitative Methods - - Single Equation Models; Single Variables - - - Instrumental Variables (IV) Estimation
    • C36 - Mathematical and Quantitative Methods - - Multiple or Simultaneous Equation Models; Multiple Variables - - - Instrumental Variables (IV) Estimation
    • J13 - Labor and Demographic Economics - - Demographic Economics - - - Fertility; Family Planning; Child Care; Children; Youth

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