The textbook approach of statisticians to confounding is quite different and rests on an idea most effectively advocated by R. A. Fisher: the randomized controlled trial (RCT). Fisher was exactly right, but not for exactly the right reasons. The randomized controlled trial is indeed a wonderful invention—but until recently the generations of statisticians who followed Fisher could not prove that what they got from the RCT was indeed what they sought to obtain. They did not have a language to write down what they were looking for—namely, the causal effect of X on Y.
