[roc]

> "drug A show 50% vs. 20% efficacy vs. placebo and drug B showed 70% vs. 40% efficacy vs. placebo"

Which raises a further (or more basic) confounding factor: the placebo effect isn't fixed.

It does vary between trials and even appears to be steadily increasing in potency over time. [1]

So first-to-market drugs have an added advantage when naively considering "improvement vs placebo" -- as their test were run years ago, when the placebo effect itself was a weaker opponent.

[1] http://www.wired.com/medtech/drugs/magazine/17-09/ff_placebo...