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Patient enrollment in medical trials: Selection bias in a randomized experiment

  • Malani, Anup

Self-selection can bias estimates of treatment effects from randomized experiments if one is interested in extrapolating results to the general population. This paper notes that there is an isomorphism between the Roy model for the sorting of workers into sectors and the decision of subjects to participate in randomized experiments. The main implication is that, as the probability of receiving active treatment rises, patients who are less optimistic about new treatment will begin to enroll and estimates of treatment effects will fall. This, in turn, implies that selection bias is positive. These findings are confirmed with data from trials of ulcer medications.

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File URL: http://www.sciencedirect.com/science/article/B6VC0-4SFXKBB-1/1/1450317b361932fa184156febd9835c1
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Article provided by Elsevier in its journal Journal of Econometrics.

Volume (Year): 144 (2008)
Issue (Month): 2 (June)
Pages: 341-351

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Handle: RePEc:eee:econom:v:144:y:2008:i:2:p:341-351
Contact details of provider: Web page: http://www.elsevier.com/locate/jeconom

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  1. Hadar, Josef & Russell, William R, 1969. "Rules for Ordering Uncertain Prospects," American Economic Review, American Economic Association, vol. 59(1), pages 25-34, March.
  2. James J. Heckman & Jeffrey A. Smith, 1995. "Assessing the Case for Social Experiments," Journal of Economic Perspectives, American Economic Association, vol. 9(2), pages 85-110, Spring.
  3. Tomas Philipson, 1999. "External Treatment Effects and Program Implementation Bias," Working Papers 9929, Harris School of Public Policy Studies, University of Chicago.
  4. Heckman, James J & Honore, Bo E, 1990. "The Empirical Content of the Roy Model," Econometrica, Econometric Society, vol. 58(5), pages 1121-49, September.
  5. Heckman, James J, 1996. "Randomization as an Instrumental Variable: Notes," The Review of Economics and Statistics, MIT Press, vol. 78(2), pages 336-41, May.
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