It is easy to dismiss any scientific study based on their limitations but to date, no other study has attempted to place any controls. We have mechanistic models based on incomplete transmission knowledge (is it airborne?) and we have observational studies where we look at what happened and attempt to adjust for certain variables.

It seems obvious by now that universal mask policies have not been very effective at controlling the transmission rate when compared to other variables: known and unknown. Maybe it is a little bit effective but that has not been conclusively shown yet. Where I live, the Ro value dropped below 1 before masks were required and shot well above 1 months later. Compliance is high, probably as high as any public health policy

Does it matter if other studies have done better? If no study to date has met standards, do we lower the standards until a published study rises to the occasion? I hope not. After all, the point of standards includes defense against confounding---your "other variables", known and unknown---especially in combo with motivated reasoning. During a pandemic, reason doesn't lack for motivation!

As for studies that do meet standards, they are hard, not easy, to dismiss. That work tends to get meta-analyzed and synthesized, not brushed off, at least by the reader community at large. I wish more of it got replicated, too, but that's a different thread.

Meanwhile, we still have to make decisions. But not entirely without scientific guidance. We can reason from studies of how the disease spreads and how potential countermeasures work. We can argue by analogy to what science has revealed about apparently similar phenomenon, like flu. Those aren't scientific arguments so much as other kinds of arguments hopefully informed by science. Pending better science as such, that's what we've got.

> "no assessment of whether masks could decrease disease transmission from mask wearers to others." [0]

It seems reasonable to me to think that, whatever the scientific contribution of the study, the fact that it doesn't test the primary claimed benefit of masks suggests that it is not the last word on the matter. When I say 'I would not be quick to promulgate or depend on the study', I am not dismissing the study, but recognizing its limitations, as do the authors.

It's not so obvious to me. Take for example Switzerland. Second wave hit it very hard. Since a couple of weeks it was however able to bring R0 down below 1 while keeping schools, stores and restaurants open. This is far from a controlled study, but the conclusion has to be that a combination of distancing, contact reduction and mask wearing is working. Note that Switzerland is densely populated and currently has relatively cold and dark weather.

The primary 'value' of mask mandating is to discourage shopping, going outside, and use of public transit - since masks are generally unpleasant and asocial.

Once these factors are removed its unlikely that mask wearing provides any value beyond security theatre.

> variable adherence

But that's the point.

We know that distancing works. We know that hygiene works. We don't yet know whether masks work or not, but we do struggle to find benefit when research is done (and this includes for source control -- there's plenty of research on that).

When scientists claim "masks work, we know they work, and we know they work well" they risk feeding a narrative that we can go about our normal day to day life so long as we wear a mask. That's untrue. We still need to distance, we still need scrupulous hygiene routines.

They also feed into a narrative that people not wearing masks are causing harm, which leaves those people open to harassment and attack.