Previously, the definition of "works" was "can be shown to be significantly better than placebo" That's what they're testing -- except, on a subgroup which is

Previously, the definition of "works" was "can be shown to be significantly better than placebo" That's what they're testing -- except, on a subgroup which is less sensitive to placebos. If a drug works on this subgroup, and if (the assumption) the drug effect is independent of the placebo effect, then you infer it's better than a placebo on the whole population, though you haven't directly tested this. Placebo effects don't vanish when you're given a real drug. Roughly, when you're testing a drug against a placebo, you're measuring {drug effect + placebo effect} against {placebo effect}. If drug and placebo are independent, than subtracting some "placebo effect" from both sides, equally, gives you the same comparison except with less statistical variation -- less "noise". It's still possible that the drug and placebo effect are interacting in an unknown way -- if the drug works, and separately it weakens the placebo effect, then this test gives you the wrong inference. This adds some epistemic uncertainty, though maybe less uncertainty than the statistical uncertainty in the ordinary trials. Obviously an issue. What this is isn't is biased. It's not set up in a way to make drugs seem systematically better: it's set up to find more drugs that actually are better.