confound
n. in an experiment, an independent variable that is conceptually distinct but empirically inseparable from one or more other independent variables. Confounding makes it impossible to differentiate that variable’s effects in isolation from its effects in conjunction with other variables. For example, in a study of high-school student achievement, the type of school (e.g., private vs. public) that a student attended prior to high school and his or her prior academic achievements in that context are confounds. Also called confounding variable.