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The International Journal of Biostatistics

Ed. by Hubbard, Alan E. / van der Laan, Mark J.

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Extended Instrumental Variables Estimation for Overall Effects

Marshall M Joffe1 / Dylan Small2 / Thomas Ten Have3 / Steve Brunelli4 / Harold I Feldman5

1University of Pennsylvania

2University of Pennsylvania

3University of Pennsylvania

4University of Pennsylvania

5University of Pennsylvania

Citation Information: The International Journal of Biostatistics. Volume 4, Issue 1, ISSN (Online) 1557-4679, DOI: 10.2202/1557-4679.1082, April 2008

Publication History

Published Online:
2008-04-07

We consider a method for extending instrumental variables methods in order to estimate the overall effect of a treatment or exposure. The approach is designed for settings in which the instrument influences both the treatment of interest and a secondary treatment also influenced by the primary treatment. We demonstrate that, while instrumental variables methods may be used to estimate the joint effects of the primary and secondary treatments, they cannot by themselves be used to estimate the overall effect of the primary treatment. However, instrumental variables methods may be used in conjunction with approaches for estimating the effect of the primary on the secondary treatment to estimate the overall effect of the primary treatment. We consider extending the proposed methods to deal with confounding of the effect of the instrument, mediation of the effect of the instrument by other variables, failure-time outcomes, and time-varying secondary treatments. We motivate our discussion by considering estimation of the overall effect of the type of vascular access among hemodialysis patients.

Keywords: instrumental variables; causal inference

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