1. A situation in which the effects of two or more processes are not separated; the distortion of the apparent effect of an exposure on risk, brought about by the association with other factors that can influence the outcome.
2. A relationship between the effects of two or more causal factors observed in a set of data, such that it is not logically possible to separate the contribution of any single causal factor to the observed effects.
Stedman’s Medical Dictionary © Wolters Kluwer Health. All rights reserved.