So, in Figure 2 Intervention is an ideal intervention on Treatment. Intervening on Treatment disrupts the evidential relationship with Gender—for example, by controlling for the proportion of male and female patients in each sample—so that any remaining probabilistic relationship between treatment and recovery can only be explained by having taken the treatment. Such an experimental design, where Treatment and Gender are made probabilistically independent, suffices to rule out association reversal (cf.  Section 2.2).