Non-Parametric Inference for the Effect of a Treatment on Survival Times with Application in the Health and Social Sciences

Xavier de Luna () and Per Johansson
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Xavier de Luna: Umeå University

No 3966, IZA Discussion Papers from Institute of Labor Economics (IZA)

Abstract: In this paper we perform inference on the effect of a treatment on survival times in studies where the treatment assignment is not randomized and the assignment time is not known in advance. Two such studies are discussed: a heart transplant program and a study of Swedish unemployed eligible for employment subsidy. We estimate survival functions on a treated and a control group which are made comparable through matching on observed covariates. The inference is performed by conditioning on waiting time to treatment, that is time between the entrance in the study and treatment. This can be done only when sufficient data is available. In other cases, averaging over waiting times is a possibility, although the classical interpretation of the estimated survival functions is lost unless hazards are not functions of waiting time. To show unbiasedness and to obtain an estimator of the variance, we build on the potential outcome framework, which was introduced by J. Neyman in the context of randomized experiments, and adapted to observational studies by D. B. Rubin. Our approach does not make parametric or distributional assumptions. In particular, we do not assume proportionality of the hazards compared. Small sample performance of the estimator and a derived test of no treatment effect are studied in a Monte Carlo study.

Keywords: employment subsidy; heart transplant; matching estimator; observational study; potential outcome; survival function (search for similar items in EconPapers)
JEL-codes: C12 C13 C14 (search for similar items in EconPapers)
Pages: 29 pages
Date: 2009-01
New Economics Papers: this item is included in nep-ecm and nep-hea
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Citations: View citations in EconPapers (9)

Published - published in: Journal of Statistical Planning and Inference, 2010, 140 (7), 2122-2137

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