[JackeJR]

I don't think the parent's point was that we ignore evidence but that in the absence of evidence (as opposed to evidence suggesting the contrary), we should use priors to guide what we do. In this case, while there are no double blind randomised studies that suggest that widespread mask use reduces R0, priors tell us that masks use protect against infection in other settings.

If we were to weigh the priors, the existing evidence would be leaving towards mask use having a protective effect. The question that we should ask ourselves is, what if the reality turns out to be different? There are 2 scenarios. First, mask use is harmful and the second, mask use has no effect on transmission. The first is very unlikely given what we know and the second will mean that if mask use is encouraged, it will be wasted resources for no gain. If these resources that were wasted were easily obtainable i.e. masks made of old clothing etc, then the downsides aren't serious at all but could have very good upsides if the priors were right.

So I agree, that we should encourage widespread home-made masks use and leave the disposable ones to the healthcare workers.

[ghostpepper]

How can you rule out the possibility that mask use has a net negative effect so easily?

[the8472]

Wearing masks is common in several asian countries even before c19 was a thing and I'm not aware of anyone showing that it's causing harm at the population level. I consider that reasonable evidence that wearing them has no significant negative physiological effects. I could see negative behavioral effects such as making people more careless because they're feeling safer. But again, effective containment in above-mentioned countries would also serve as evidence against that actually being an issue.

[traverseda]

The hypothesis that face masks have a net negative effect is a very strong claim, before considering it we'd need some evidence that points in that direction.

I guess if you believe that's actually true, you should be advocating for doctors to stop wearing masks...

But that's not something we do, because we have enough priors that masks help that we will continue to use them.

[craftinator]

Simple reasoning. We know that viruses can be transmitted through saliva. Covid-19 generally presents with a cough. Coughs aerosolize saliva. Wearing a mask or face covering catches most particles, and absorbs energy from all particles, so they dont travel as far. Less virus mass, and a smaller projection plume will result in less spread. Less spread results in a lower R0.

I realize that you are just enjoying being contrary here, but please try to think through your argument and ensure it isn't incorrect in itself before posting.

[srean]

Ah! prefer inaction to potentially imperfect action argument, I see.

[nsomaru]

Also, how does "what we know" make this unlikely?