When Zweig says, "If you need 500,000 or 1 million people to find a benefit, how marginal is that benefit?" that means that he doesn't realize that a 21% point estimate in that study with 0% in the error bar means that 42% is also in the error bar. This is not marginal! The point estimate is not marginal either, so when Zweig says that requiring a larger study size means that the effect is marginal, he is either being intentionally deceiving, or he does not understand statistics. I gave him the benefit of the doubt.

> if your drug fails to show statistically significant efficacy in testing that means you don’t get approval.

He doesn't make that point, but that one is also rather silly. If all of our evidence suggests mask effectiveness among elementary school students (some by mechanism, some by simulation, and some by evaluating mask policies on other groups), including the study he pointed to, the correct decision is to require masks for elementary school students. The harms are negligible, and the benefits for reducing community spread are large. The risk for approving an ineffective drug is far larger.

Elsewhere, you made the point that we don't know if masks should be required for toddlers. That I agree with, but that isn't a point that Zweig has made.