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Sensitivity analysis of the unconfoundedness assumption in observational studies

  • de Luna, Xavier


    (Department of Statistics, Umeå University)

  • Lundin, Mathias

    (Department of Statistics, Umeå University)

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    In observational studies, the estimation of a treatment effect on an outcome of interest is often done by controlling on a set of pre-treatment characteristics (covariates). This yields an unbiased estimator of the treatment effect when the assumption of unconfoundedness holds, that is, there are no unobserved covariates affecting both the treatment assignment and the outcome. This is in general not realistically testable. It is, therefore, important to conduct an analysis about how sensitive the inference is with respect to the unconfoundedness assumption. In this paper we propose a procedure to conduct such a Bayesian sensitivity analysis, where the usual parameter uncertainty and the uncertainty due to the unconfoundedness assumption can be compared. To measure departures from the assumption we use a correlation coefficient which is intuitively comprehensible and ensures that the results of sensitivity analyses made on different evaluation studies are comparable. Our procedure is applied to the Lalonde data and to a study of the effect of college choice on income in Sweden.

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    Paper provided by IFAU - Institute for Evaluation of Labour Market and Education Policy in its series Working Paper Series with number 2009:12.

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    Length: 21 pages
    Date of creation: 10 Jun 2009
    Date of revision:
    Publication status: Published as de Luna, Xavier and Mathias Lundin, 'Sensitivity analysis of the unconfoundedness assumption with an application to an evaluation of college choice effects on earnings' in Journal of Applied Statistics, 2014, pages 1767-1784.
    Handle: RePEc:hhs:ifauwp:2009_012
    Contact details of provider: Postal: IFAU, P O Box 513, SE-751 20 Uppsala, Sweden
    Phone: (+46) 18 - 471 70 70
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    1. LaLonde, Robert J, 1986. "Evaluating the Econometric Evaluations of Training Programs with Experimental Data," American Economic Review, American Economic Association, vol. 76(4), pages 604-20, September.
    2. John Copas & Shinto Eguchi, 2001. "Local sensitivity approximations for selectivity bias," Journal of the Royal Statistical Society Series B, Royal Statistical Society, vol. 63(4), pages 871-895.
    3. John Copas & Shinto Eguchi, 2005. "Local model uncertainty and incomplete-data bias (with discussion)," Journal of the Royal Statistical Society Series B, Royal Statistical Society, vol. 67(4), pages 459-513.
    4. Sander Greenland, 2005. "Multiple-bias modelling for analysis of observational data," Journal of the Royal Statistical Society Series A, Royal Statistical Society, vol. 168(2), pages 267-306.
    5. Guildo W. Imbens, 2003. "Sensitivity to Exogeneity Assumptions in Program Evaluation," American Economic Review, American Economic Association, vol. 93(2), pages 126-132, May.
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