Confounding

Abstract

In a study the treatment effects may be better in the males than they are in the females. This difference in efficacy may not influence the overall assessment as long as the numbers of males and females in the treatment comparison are equally distributed. If, however, many females received the new treatment, and many males received the control treatment, a peculiar effect on the overall data analysis will be observed: the overall regression line of treatment modalities versus treatment outcomes (efficacies) will become close to horizontal, giving rise to the erroneous conclusion that no difference in efficacy exists between treatment and control. This phenomenon is called confounding, and may have a profound effect on the outcome of the study. This chapter shows how to assess confounded studies with continuous outcome data. Confounded studies with binary outcome data are reviewed in the Chap. 40.