Causal assessment of surrogacy in a meta-analysis of colorectal cancer trials.
When the true end points (T) are difficult or costly to measure, surrogate markers (S) are often collected in clinical trials to help predict the effect of the treatment (Z). There is great interest in understanding the relationship among S, T, and Z. A principal stratification (PS) framework has been proposed by Frangakis and Rubin (2002) to study their causal associations. In this paper, we extend the framework to a multiple trial setting and propose a Bayesian hierarchical PS model to assess surrogacy. We apply the method to data from a large collection of colon cancer trials in which S and T are binary. We obtain the trial-specific causal measures among S, T, and Z, as well as their overall population-level counterparts that are invariant across trials. The method allows for information sharing across trials and reduces the nonidentifiability problem. We examine the frequentist properties of our model estimates and the impact of the monotonicity assumption using simulations. We also illustrate the challenges in evaluating surrogacy in the counterfactual framework that result from nonidentifiability.
Department of Biostatistics, University of Michigan, Ann Arbor, MI 48109, USA. yunlisph@umich.edu
Yun
Y
Li
Jeremy M G
JM
Taylor
Michael R
MR
Elliott
Daniel J
DJ
Sargent
D001499:Bayes Theorem; D014408:Biomarkers, Tumor / Q000032:analysis*; D002986:Clinical Trials as Topic / Q000379:methods*; D015179:Colorectal Neoplasms / Q000737:chemistry / Q000188:drug therapy; D003198:Computer Simulation; D006801:Humans; D015201:Meta-Analysis as Topic; D015233:Models, Statistical
D014408:Biomarkers, Tumor
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