Confronting the confounders: the meaning, detection, and treatment of confounders in research.

When one variable is studied to try to explain another, the relationship between them may be biased by a third variable. The bias, known as "confounding," is common and must be minimized in research. This description is deceptively simple, though. Identifying confounding is complex but can be reduced to a stepped procedure. By way of examples, this article describes confounding and how to recognize it.