[svnt]

They aren’t summing effects. An effect is not cancelled by an inverse effect or as you put it, backfire.

The methodology should (I haven’t investigated theirs in detail) not be susceptible to this, and I doubt a mean of effects would make it through peer review for reasons including the ones you’ve mentioned.

[mikkergp]

Where are they getting an effect size of .08 if not by mathing a bunch of other effect sizes.