Abstract
Clinical trials with rare or distant outcomes are usually designed to be large in size and long term. The resource-demand and time-consuming characteristics limit the feasibility and efficiency of the studies. There are motivations to replace rare or distal clinical endpoints by reliable surrogate markers, which could be earlier and easier to collect. However, statistical challenges still exist to evaluate and rank potential surrogate markers. In this paper, we define a generalized proportion of treatment effect for survival settings. The measure’s definition and estimation do not rely on any model assumption. It is equipped with a consistent and asymptotically normal non-parametric estimator. Under proper conditions, the measure reflects the proportion of average treatment effect mediated by the surrogate marker among the group that would survive to mark the measurement time under both intervention and control arms.
Highlights
The HPTN (HIV Prevention Trial Network) 052 study is an HIV prevention trial conducted across several continents
A surrogate marker in clinical trials is considered to be “a laboratory measurement or physical sign used as a substitute for a clinically meaningful endpoint that measures directly how a patient feels, functions, or survives and that is expected to predict the effect of the therapy” [1]
The ratio reflects the proportion of the average treatment effect mediated by the surrogate measure for the subgroup surviving to marker measurement anyway
Summary
The HPTN (HIV Prevention Trial Network) 052 study is an HIV prevention trial conducted across several continents. It is considered to be valid if one could correctly conclude treatment effect on the clinical endpoint by using the marker [2,3]. In this context, how to validate surrogate markers for a clinically meaningful endpoint are especially important. A surrogate marker is considered to be valid if one could correctly conclude the treatment effect on the clinical endpoint by using that marker.
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