[kmacleod]

When I did the pre-2020 deep-dive I found the studies to be uniformly about the mechanics of the mask (hole size and particle size) and therefore the conclusions uniform on that front.

It was only after 2020 that any studies were done on effectiveness in use. The results are a lot more positive there. However, it was still difficult to do controlled studies so the results aren't as strong as one would like.

[wrp]

A big problem with all the discussion about masks is that there are at least three different types of study, and people tend to mix the conclusions.

1. Epidemiological: "Town A mandated masks and town B didn't. Was there any difference in reported rate of pathogen spread?" Reviews over the past century of epidemic responses indicated no overall benefit.

2. Clinical: "In a controlled situation, was there a difference in rate of pathogen spread between the mask-user group and the non-mask group?" There was soft support for some benefit in non-sterile, close-contact environments.

3. Laboratory: "On a laboratory bench, what degree of pathogen capture was achieved by the mask apparatus?" These studies assume that performance on the bench correlates to performance in the field. The N95 mask is a case in point. On the bench, it performs better, but reviews of clinical studies didn't find a strong effect in field use.