Covariates that affect the outcome of a disease are often incorporated into the design and analysis of clinical trials. This serves two main purposes: 1. To improve the credibility of the trial results by demonstrating that any observed treatment effect is not accounted for by an imbalance in patient characteristics, and 2. To improve statistical efficiency. In this paper, we review procedures for the adjustment of treatment effects for the influence of covariates and discuss some statistical and regulatory issues on the applications of these procedures.
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