 One of the aims behind the methodology of randomized controlled trials (RCTs) is to eliminate the effect of potential confounders on whether a person is treated or not. This was described in  Section 2.2  as row-uniform design (for experiments with categorical data). For example, if we ensure the same proportion of both genders in the treatment and control group, the same prevalence of different age groups, etc., we know that association reversal (AR) cannot occur with respect to those third variables, and also the amalgamation paradox (AMP) is ruled out for many measures.