 Although the definiens of a comparative cp-law relating \(X\) with \(Y\) refers to “all \(X\)-independent variables”, comparative cp-laws are nevertheless empirically testable by the method of randomized experiments (cf. Fisher 1951). In this method, one randomly splits a sample into two subgroups, an “experimental group” and a “control group”, then enforces an increase of the value of \(X\) on the experimental but not on the control group, and finally compares the two samples concerning the value of \(Y\). Since the split of the original sample was random, experimental and control group will agree in their distribution of all \(X\)-independent remainder variables, apart from random errors. Thus, one can apply this method without knowing which \(X\)-independent variables are causally relevant for \(Y\) and which are not. If there is a significant change of the value of \(Y\) in the experimental group compared with the control group, the cp-law “\(X\)-increase leads to an \(Y\)-change” is confirmed (strictly speaking only the restriction of this law to the population from which the sample has been taken is strongly confirmed, while confirmation of the unrestricted cp-law requires tests for a variety of different “populations”, i.e., distributions of \(X\)-independent remainder variables). On the other hand, if there is no significant change of \(Y\)’s value, the cp-law is strongly disconfirmed, even in its unrestricted form. This does not mean that the method of randomized controlled experiment is free from error possibilities. In particular, the experimentally induced change of \(X\)’s value may have smuggled in unrecognized \(X\)-dependent variables (i.e., unrecognized side-effects) which are partly responsible for the resulting change of \(Y\). For example, in a teaching experiment comparing two teaching methods (e.g., the new method and the old method), the new teaching method may come out as more successful than the old one—yet not because of intrinsic properties of the new method, but just because the fact that the teaching method was new has increased the motivation of its teachers.