3 ms·

That is not an accurate summary of the study. Emphasis mine: > Limitation: Inconclusive results, missing data, variable adherence, patient-reported findings on

That is not an accurate summary of the study. Emphasis mine: > Limitation: Inconclusive results, missing data, variable adherence, patient-reported findings on home tests, no blinding, and no assessment of whether masks could decrease disease transmission from mask wearers to others. > The recommendation to wear surgical masks to supplement other public health measures did not reduce the SARS-CoV-2 infection rate among wearers by more than 50% in a community with modest infection rates, some degree of social distancing, and uncommon general mask use. The data were compatible with lesser degrees of self-protection. I don't think any public health experts are saying "wear a mask and you'll be safe", they're saying "if everybody wears a mask, that will slow the infection rate". A study of a community with "uncommon general mask use" does not dispute this. Finally, I don't think it's clear that a randomized controlled trial is the best method to answer this question. Aside from ethical concerns, you can't give someone a placebo mask. Shouldn't we assume that people will behave differently when they're wearing a mask?

timr 6y ago
I made an accurate summary of the study. From the Results: "Although the difference observed was not statistically significant, the 95% CIs are compatible with a 46% reduction to a 23% increase in infection." The points you are raising about limitations in no way affect the conclusion of the work. Short of putting infected people in a room with uninfected people, there is no ethical way to test the hypothesis that "masks could decrease disease transmission from mask wearers to others". But since it's pretty unlikely that masks are effective in one direction only, this is the highest-quality evidence we have that they have no effect in one of the two directions. > Finally, I don't think it's clear that a randomized controlled trial is the best method to answer this question. A randomized controlled trial is always the gold standard for an intervention of this sort. But yeah, you can't do one for that hypothesis. So you're stuck with something that is fundamentally un-falsifiable. The best you can do is try to do what people have done so far: look at populations, and see if mask mandates make any difference, or ask people who caught Covid if they wore masks, or do similar things within families. This is called retrospective cohort analysis, and it is low-quality evidence, at best. > Aside from ethical concerns, you can't give someone a placebo mask. Shouldn't we assume that people will behave differently when they're wearing a mask? Yes, we should assume that this might happen. It could well be true that wearing a mask makes people be more careless about distancing, for example. This is called "risk compensation", and is a well-known phenomenon in public health.
- PaulDavisThe1st 6y ago
  It seems to me that you're trying to fight two battles at once. 1. do masks inhibit production of and exposure to aerosols carrying SARS-COV-2? This seems (to me) to me clearly established, and essentially irrefutable. 2. do mask mandates reduce the spread of COVID19? this is an entirely different question, and has almost nothing whatsoever to do with the abilities of masks referenced in (1) above. I would suggest that we know that the answer to (1) is yes, without doubt, but we have only hand-wavy answers to (2). That's still quite different from what you're claiming.
  - timr 6y ago
    > do masks inhibit production of and exposure to aerosols carrying SARS-COV-2? This seems (to me) to me clearly established, and essentially irrefutable. Aerosols? It's far from established. In fact, it's a dubious claim, unless you're far more specific about what you mean by "masks". The best laboratory studies show that properly fitted respirators (i.e. as used in hospitals), can reduce aerosol emissions. But few people are wearing respirators, and essentially nobody is fitting them correctly. Cloth masks? Surgical masks? Cup masks? About the only claim you can make is that they might reduce heavy droplets and then, only by about 30% or so. There's no reason to believe they have any effect on aerosol emission. Michael Osterholm covered this extensively: https://www.cidrap.umn.edu/covid-19/podcasts-webinars/special-ep-masks https://www.cidrap.umn.edu/covid-19/podcasts-webinars/specia... Anyone who has done a mask fitting -- where they put you in a room with vaporized stuff that you can taste to detect leaks -- will tell you how difficult it is to get an aerosol-resistant seal on a mask. The chances that the general public is doing it is 0%.

timr 6y ago

I made an accurate summary of the study. From the Results: "Although the difference observed was not statistically significant, the 95% CIs are compatible with a 46% reduction to a 23% increase in infection." The points you are raising about limitations in no way affect the conclusion of the work. Short of putting infected people in a room with uninfected people, there is no ethical way to test the hypothesis that "masks could decrease disease transmission from mask wearers to others". But since it's pretty unlikely that masks are effective in one direction only, this is the highest-quality evidence we have that they have no effect in one of the two directions. > Finally, I don't think it's clear that a randomized controlled trial is the best method to answer this question. A randomized controlled trial is always the gold standard for an intervention of this sort. But yeah, you can't do one for that hypothesis. So you're stuck with something that is fundamentally un-falsifiable. The best you can do is try to do what people have done so far: look at populations, and see if mask mandates make any difference, or ask people who caught Covid if they wore masks, or do similar things within families. This is called retrospective cohort analysis, and it is low-quality evidence, at best. > Aside from ethical concerns, you can't give someone a placebo mask. Shouldn't we assume that people will behave differently when they're wearing a mask? Yes, we should assume that this might happen. It could well be true that wearing a mask makes people be more careless about distancing, for example. This is called "risk compensation", and is a well-known phenomenon in public health.

PaulDavisThe1st 6y ago
It seems to me that you're trying to fight two battles at once. 1. do masks inhibit production of and exposure to aerosols carrying SARS-COV-2? This seems (to me) to me clearly established, and essentially irrefutable. 2. do mask mandates reduce the spread of COVID19? this is an entirely different question, and has almost nothing whatsoever to do with the abilities of masks referenced in (1) above. I would suggest that we know that the answer to (1) is yes, without doubt, but we have only hand-wavy answers to (2). That's still quite different from what you're claiming.
- timr 6y ago
  > do masks inhibit production of and exposure to aerosols carrying SARS-COV-2? This seems (to me) to me clearly established, and essentially irrefutable. Aerosols? It's far from established. In fact, it's a dubious claim, unless you're far more specific about what you mean by "masks". The best laboratory studies show that properly fitted respirators (i.e. as used in hospitals), can reduce aerosol emissions. But few people are wearing respirators, and essentially nobody is fitting them correctly. Cloth masks? Surgical masks? Cup masks? About the only claim you can make is that they might reduce heavy droplets and then, only by about 30% or so. There's no reason to believe they have any effect on aerosol emission. Michael Osterholm covered this extensively: https://www.cidrap.umn.edu/covid-19/podcasts-webinars/special-ep-masks https://www.cidrap.umn.edu/covid-19/podcasts-webinars/specia... Anyone who has done a mask fitting -- where they put you in a room with vaporized stuff that you can taste to detect leaks -- will tell you how difficult it is to get an aerosol-resistant seal on a mask. The chances that the general public is doing it is 0%.