Recently there has been a couple of meta-analyses investigating heterogeneous treatment effects by analyzing the ratio of the outcome variances in the treatment and control group. The argument made in these articles is that if individuals differ in their response, then observed variances in the treatment and control group in RCTs should differ. For instance, Winkelbeiner et al. (2019) write:
The SDs of the pretreatment and posttreatment outcome difference scores in the treatment and control groups consist of the same variance components, including the within-patient …