The latest EconTalk episode talks about this: https://www.econtalk.org/nassim-nicholas-taleb-on-the-pandem... ... Once the Pandemic hit, we should have worn masks. Statistical studies aren't the only form of human knowledge - we understand that when we speak, air and saliva leave our mouth, carrying viruses along. Masks catch air and saliva (and as you say, have low cost). Therefore, wearing masks makes sense as a matter of logic. We don't need to drag p-values into everything.

Masks reduce spread of the virus by already infected people. They work because even people who don't even know they are sick are wearing them from the beginning to the end of their infection. When it comes to exponential growth it doesn't matter if the masks reduce infection rate by 10%, 1% or even 0.1%. Alternatively, even if masks don't work physically there is a psychological component to wearing masks that can reduce the infection rate by reminding people that there is a virus out there and as long as you are wearing the mask you should be extra careful.

There's not much evidence to support anything in your comment.

If masks were so effective it would be easy to find that benefit in any of the good quality trials that have been run, and we don't see that benefit. To see any benefit of mask wearing we have to drop the quality of evidence right down.

One thing often missing from these discussions is the concept of "number needed to treat". How many people need to wear a mask to prevent one additional infection?

https://www.fhi.no/globalassets/dokumenterfiler/rapporter/20...

> Given the low prevalence of COVID-19 currently, even if facemasks are assumed to be effective, the difference in infection rates between using facemasks and not using facemasks would be small. Assuming that 20% of people infectious with SARS-CoV-2 do not have symptoms, and assuming a risk reduction of 40% for wearing facemask, 200000 people would need to wear facemasks to prevent one new infection per week in the current epidemiological situation.

I was under the impression that masks only work to protect you from transmitting to others. Has that aspect not been studied yet?

Or are you talking about the efficacy of masks protecting the person that wears it?

Appreciate your time.

The largest reduction in rate of transmission is when the infected person is wearing a mask. However if both the infected, and uninfected person are wearing masts, it drops just a little bit lower. But you're right that if an unmasked infected person comes in contact with a masked healthy person, the masked person is still very likely to get infected.

It's much like flossing. The mechanism is so obvious, we didn't need a statistical study to be confident. We now have statistical evidence from Covid-19 spread.

No idea. I’m not an expert.

My physics intuition says that air filter is almost equally effective whereever it is (your mouth or another person’s mouth). It depends on the details though - how big the virus is? How far does it travel? How much of it comes out “dry” vs in water droplets? How big are these water droplets? What’s the distance it can travel in a droplet vs “dry”? And so on and so on. My prior says that eyes aren’t a big transmission factor (as the virus has particular affinity towards lung cell receptors) and that the only way that mask efficiency is radically different depending on who’s wearing it is, if the virus is mostly exhaled in water droplets and most of them evaporate in the next 1-2 meters (so when you inhale through a mask, it doesn’t filter the tiny virus particles, whereas exhaling into a mask does filter the less tiny water droplets).

But the bigger point is, it doesn’t matter. Masks can help, and that should be enough to make a decision, like a general rule or recommendation to wear masks (or face coverings).

The last few years have made it very clear that worldwide the medicine regulation sector sucks at cost-benefit analysis.