Clinical Trials

■■❚❙❘Chapter 26ConfoundingDuolao Wang, Tim Clayton, and Ameet BakhaiThe aim of a clinical trial is to provide an accurate estimateof the effect of a therapy or procedure on an outcomesuch as death, compared with the effect of a control, suchas a placebo. However, the estimate of this effect can bedistorted by various sources of bias during the design,conduct, and analysis of a study. Confounding is one suchbias that can distort the estimate of the treatment effect,due to an imbalance across treatment groups of a variableassociated with the outcome. In this chapter, we describewhat a confounding factor is and how it can impact a clinicaltrial, explain how confounding factors can be identified,and introduce some methods that can be used to controlconfounders during study design and analysis.295