Instrumental variables
In statistics, econometrics, epidemiology and related disciplines, the quasi-experimental method of instrumental variables (IV) is used to estimate causal relationships when controlled experiments are not feasible or when a treatment is not successfully delivered to every unit in a randomized experiment. Intuitively, IVs are used when an explanatory (also known as independent or predictor) variable of interest is correlated with the error term (endogenous), in which case ordinary least squares and ANOVA give biased results.