Caption: Confounding
Text: When examining the association between an exposure and an outcome, other exposures (ie., other risk factors) may distort the magnitude of association if they are unequally distributed between the groups being compared. For example, in studying the association between heavy smoking and lung cancer, the two exposure groups (heavy smokers & non-smokers) might differ substantially in age distribution, and age is an independent risk factor for lung cancer. If smokers were older than non-smokers, then the unequal age distribution would exaggerate the strength of association between smoking and lung cancer.