There's a massive number of studies. A selection of 3 links out of 100+ would only reveal my biases. I'd rather just discuss my summation of the research and if there's something in particular you'd like to see, share that.
* Various studies of droplet propagation, which show well-fitting masks reduce droplets significantly. In theory, this should reduce spread.
* Many confounded observational and cohort studies tied to voluntary compliance with mask guidelines that show a lower risk of infection or secondary transmission. They are confounded because voluntary compliance with this measure increases the likelihood of general caution. Many show somewhat large effect sizes.
* Many population based trend-line studies/other ecological studies that show post requiring it as a public health measure in various environments, that daily case counts began to decline by .4% to 2.0% per day.
The studies in the second category showing larger effects are generally inconsistent with the third category, because the results in the third would be much bigger if the effect was real. And even the third category isn't great, because the mask requirement measures weren't instituted in a vacuum independent of other controls.
One of the studies was an ecological study comparing mask wearing rates in many locales (some with compulsory requirements, and some without) and their change over time vs. disease growth rates.
Another measured case growth in a hospital community where there was a very strictly enforced mandate for patients compared to the rate of case growth before, so compliance is a small factor.
It's very likely that masks help. It's also very likely that the effect is relatively small. But even a tiny effect can become a big one when raised to a big power-- 1.1^20 is 6.7x growth in cases, and 1.07^20 is 3.8x.
I'd have liked this guidance change in masks to come a week or two later. Keeping another couple weeks of somewhat sharper decline in cases means a lot fewer people affected through the rest of the pandemic.
Your conclusions here don’t really seem in line with your comment about still not knowing if masks work.
Not sure why you feel like this is a worthy hair to split.
This kind of attitude is why the western response could have been better. Western medicine is hews rigorously close to the “do no harm” ideal and interpret it that you need to have conclusive evidence before recommending a treatment, even something as harmless as mask wearing.
In Asian countries they just do it and so what if it hasn’t been demonstrated as a causal factor in a dozen studies.
Lay people see the indecision, the hemming and hawing, the hand wringing.
The cdc says shit like people shouldn’t wear masks.
This shit is actively harmful and thousands of people have died because of it.
We have confounded evidence of a weak effect. If I had to bet (and we all have had to), I'd say they do have a small benefit on a population scale. But if more evidence showed up saying they didn't, I would be completely unsurprised.
I think it's worthwhile to have doubt and be skeptical.
I'll note that, at the beginning of the pandemic, I was saying that masks may or may not work, but they should still be recommended at a time that the CDC was implying that they might even be harmful.
This is all completely consistent with what I originally said: "To be honest, we still don't really know if masks work. They look like they probably do something, but the evidence is weak and the effect size small."
