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Comment by GordonS | Hacker News Reader

I think if you're going to make a post like this, it's reasonable to expect that you present some actual evidence, or is your whole argument that we should ignore evidence?

"Homemade masks appear to be reasonably effective" is hardly a compelling case.

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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.

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

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

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

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.

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.

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.

Another study on homemade masks: https://www.researchgate.net/publication/258525804_Testing_t... "Both masks significantly reduced the number of microorganisms expelled by volunteers, although the surgical mask was 3 times more effective in blocking transmission than the homemade mask. Our findings suggest that a homemade mask should only be considered as a last resort to prevent droplet transmission from infected individuals, but it would be better than no protection."

This is by no means a personal attack but this is approximately the thought pattern the parent comment is arguing against.

Absence of evidence does not prevent you from making decisions or otherwise coming to conclusions. The fact is, you can make decisions with no evidence at all. Your outcome may be no better than chance but also likely no worse.

Not making a decision can be worse than chance, especially in time critical or low information environments and if you always “wait for the evidence” you will end up being worse than a magic 8-ball at the most crucial moments.

There is no "not making a decision". It's not that you can make decisions without evidence, you must make a decision even without evidence. Not wearing a mask is as much as a decision as wearing one.

Professional and Home-Made Face Masks Reduce Exposure to Respiratory Infections among the General Population. Marianne van der Sande. 2008. doi:10.1371/journal.pone.0002618

https://sci-hub.tw/10.1371/journal.pone.0002618

Here's a source that supports OP's claims: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3373043

I run freesewing.org, the website linked to in the Forbes article (1). The university hospital here in Antwerp where I live is actively reaching out to the community asking them to make masks. (2) I'm not a scientist, but here's something that I can do, so I'm trying to help. I trust the doctors, that's good enough for me.

(1) https://www.forbes.com/sites/tjmccue/2020/03/20/calling-all-... (2) https://www.uza.be/mondmaskers. (in Dutch)

https://smartairfilters.com/en/blog/coronavirus-pollution-ma...

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