Pearl (1995) uses expression of the form Q = E[Y |do(X = x)] to denote the causal effect of X on Y . Where do(x) is a minimally invasive intervention that sets the value of X to x and leaves other relationships unchanged.

However, when X is non-manipulable for experimenters (for example, gender/race are non-manipulable), critics raise concern about the interpretation of the casual effect Q.