[kdbg]

https://www.science.org/doi/10.1126/science.abi9069

Unfortunately many parts of this paper are beyond me, but this study does appear to find that community level masking has an impact, but it is a study that used actual communities and tracked compliance (and impact of different interventions on encouraging making)

[twic]

AFAIK, this is the only really good study of mask-wearing. It's large (300k people!), and it's randomised. It tried two kinds of masks, "surgical" and "cloth":

> We used high-quality surgical masks that had had a filtration efficiency of 95% [standard deviation (SD) = 1%]; this is substantially higher than the filtration efficiency of the cloth masks we designed, which had a filtration efficiency of 37% (SD = 6%). These cloth masks had substantially higher filtration than common commercial 3-ply cotton masks, but lower than hybrid masks that use materials not commonly available for community members in low-resource settings (54).

The key result:

> We find clear evidence that surgical masks lead to a relative reduction in symptomatic seroprevalence of 11.1% (aPR = 0.89 [0.78,1.00]; control prevalence = 0.81%; treatment prevalence = 0.72%). Although the point estimates for cloth masks suggests that they reduce risk, the confidence limits include both an effect size similar to surgical masks and no effect at all. (aPR = 0.94 [0.78,1.10]; control: 0.67%; treatment: 0.61%).

It's a shame that even with such a large study, the phenomenon is so noisy that we can't get a strong signal here. But i think the takeaway is that masking has an effect, but it is rather small.

There's a lot more detail in the paper. Including this gem:

> We find no evidence that any of our village-level or household-level treatments, other than mask color, impacted mask-wearing. For mask-color, we see marginally significant differences, small in magnitude. In surgical mask villages, blue masks were more likely to be observed than green (adjusted percentage point difference = 0.03, [-0.00,0.06]), and in cloth mask villages, red more likely than purple (adjusted percentage point difference = -0.02, [-0.04,-0.00]). Text message reminders, incentives for village-leaders, or explicit commitment signals explain little of the observed increase in mask-wearing. Compared to self-protection messaging alone, altruistic messaging had no greater impact on mask-wearing, and twice-weekly text messages and a verbal commitment had no significant effects.

[Axien]

Actually look at the peer review of that study done by Cornell and released this December. When the actual data was analyzed it showed masks had no effect.

[twic]

Interesting - do you have a link by any chance?