Figure 3. Funnel plots of variance ratio.

Funnel plots of variance ratio between arms with the 208 studies ( Panel A) and for over-time comparison with the 95 studies for which the variance of the difference between the basal and final response was available ( Panel B). Vertical axis indicates precision for the comparison of variances; with points outside the triangle being statistically significant. Additionally, red points mark significant differences between the means, which correspond to the objective of each study to assess main treatment effects. In Panel A, points on the right indicate higher outcome variability for the treated individuals, as expected if there is patient-by-treatment interaction; similarly, points on the left correspond to lower variability, although this is compatible with traditional Evidence-Based Medicine. Eleven (5.2%) out of 208 studies reported exactly the same outcome variability in both arms. We observe more red points on the left, indicating that changes in the average, come with reductions in the variance. In Panel B, points on the right indicate higher variability in the experimental arm at the end of the study, as expected in a scenario of heterogeneous treatment effect; points on the left correspond to lower variability at the end, which implies a more homogenous response after treatment. The largest number of points on the left side indicates a majority of experimental interventions that reduce variability. In addition, several of these interventions yielded significant results in the main endpoint.