11 ms·

Surgical masks reduce Covid-19 spread, large-scale Stanford study shows

152 points by djrogers 5y ago

dragontamer 5y ago
> The researchers enrolled nearly 350,000 people from 600 villages in rural Bangladesh Wow. I was about to complain about "small n", but... an experiment of this size is not small at all. Congrats on the researchers on doing such a big study!
- cfn 5y ago
  I think it is a bit cheeky of them. They promoted the usage of masks and distancing in 600 villages totalling 350,000 people and observed the results (mask wearing plus distancing) in mosques (by sampling, not by checking each individual).
  - jerf 5y ago
    I know it's easy to get cynical about "sampling" when you see a stream of studies sampling populations of millions with n = 12 and getting p values just barely considered "significant", but that's not the fault of "sampling". That's just... gathering no data, basically, or if you prefer, going through the motions of gathering data without actually doing it.
    - cfn 5y ago
      I am not arguing with the method, I only think the language of the paper is misleading to the point that the parent commenter aparently thinks they actually analysed hundred of thousands of subjects when they just extrapolated their observations to that number. It may even be right and significant but that is not my point.
      - dragontamer 5y ago
        I've reread the article + paper with your discussion in mind, and I agree with you. It seems misleading, and I failed to understand the study from the headline / abstract. Its not a "bad" study per se, but its definitely entering clickbait. I'm still happy they conducted the study and presented their research.
- kragen 5y ago
  Maybe the relevant point is that it needed to be this big to get a P-value of less than .05, since they only got .04 even with 350,000 people. This is dramatically less effectiveness than I was expecting when I was pushing for mask mandates last year, and within a few months it was obvious that masks alone weren't having the large effect I had hoped for. Now we have quantitative estimates of how small the effect was (disappointingly small) and when it worked (cloth masks had almost no effect).
  - dragontamer 5y ago
    When 70% of people weren't affected by the experiment (13% were wearing masks before the experiment started. 60% of people didn't wear a mask after the experiment), then of course the numbers are going to be small. Seeing a measurable difference when the population only changed from 13% mask to 40%ish mask usage is pretty outstanding IMO.
    - kragen 5y ago
      I don't think that's correct; see https://news.ycombinator.com/item?id=28407881 https://news.ycombinator.com/item?id=28407881 for the argument in more detail.
      - dragontamer 5y ago
        My argument and your argument are seemingly unrelated. That means that the full matrix of situations are available: I'm correct and you're correct. I'm correct and you're wrong. I'm wrong and you're correct, and finally I'm wrong and you're wrong. ---------- So lets just try again from the top. The study shows that an 8-week mask-awareness campaign in Bangladesh across 300 villages (+300 "control" villages 2+km away where mask-awareness did NOT happen) leads to a 29% increase in mask usage and an 11% decrease in COVID19 cases. Is there anything wrong with this new, revised statement I made? It seems to be the big "A / B" test that everyone's wanted for mask studies.
        kragen 5y ago
- otabdeveloper4 5y ago
  Size of N isn't the issue, controlling for confounding variables is.
ch4s3 5y ago
> There were significantly fewer COVID-19 cases in villages with surgical masks compared with the control villages. (Although there were also fewer COVID-19 cases in villages with cloth masks as compared to control villages, the difference was not statistically significant.) This aligns with lab tests showing that surgical masks have better filtration than cloth masks. However, cloth masks did reduce the overall likelihood of experiencing symptoms of respiratory illness during the study period. I think this is probably the most interesting part, and worth watching in future studies.
- majormajor 5y ago
  It's surprising to me that cloth masks can't even do the 11% of surgical masks. Which isn't much, but surgical masks are non-optimal for many reasons. Not to mention that this doesn't seem the same as "while wearing a surgical mask you only get 11% increase in protection" but is a population-level thing. There was still non-compliance that presumably lowered the efficacy. I would've intuitively guessed that the better fit of cloth masks would make them better, but presumably the mask surface of a surgical mask has properties that offset that? Would be great to see numbers for N95 masks. Intuitively I'd assume they'd be much more effective as they have better fit + higher filtration, but of course, confirmation would be great. Fits with what we're seeing in Europe such as airlines banning cloth masks, though. The great incoherent idiocy of anti-* Americans on the issue of masks has always been that they say "cloth masks are ineffective" and propose a solution of "do nothing" instead of "get effective masks."
  - slg 5y ago
    >It's surprising to me that cloth masks can't even do the 11% of surgical masks. Just want to add clarification here. The 11% number is the community impact of the programs designed to increase mask usage. It is not the effectiveness of a mask on an individual level. That number will be much higher since as you said a number of people didn't/don't comply at a societal level.
    - majormajor 5y ago
chitowneats 5y ago
From Martin Kulldorff, esteemed (though contrarian) Harvard Med epidemiologist: "Odd that mask advocates are excited by this study. As a vaccine advocate, I would be horrified if a vaccine trial showed 11% efficacy. Based on the 95% confidence intervals, we do not even know if surgical mask efficacy is more than 0%." https://twitter.com/MartinKulldorff/status/1433202651106201607?s=20 https://twitter.com/MartinKulldorff/status/14332026511062016...
- SubiculumCode 5y ago
  I think this thread is a decent refutation that the CI lower bound was at 0: "First, the 11% reduction comes from a 30% increase in mask-use. The IV estimate (naively scaling things linearly) would thus be more like a 37% reduction in COVID from going from zero to universal masking." "Second, we find much larger effects among the elderly (a 35% reduction among 60+ without the above scaling). This suggests that the total reduction in morbidity and mortality from universal masking may be considerably larger than even the 37% number, perhaps more than 50%." "Third, it's not quite an apples to apples comparison because we are estimating the community impact of masks, whereas the vaccine studies only isolate the individual protective effect. The efficacy of vaccines at the population level may be larger than trials imply." https://twitter.com/Jabaluck/status/1433129444940599296 https://twitter.com/Jabaluck/status/1433129444940599296
- dragontamer 5y ago
  EDIT: Woops, read wrong. Lemme post the quote instead. > The observers found that just over 13% of people in the villages that received no interventions wore a mask properly, compared with more than 42% of people in the villages where each household received free masks and in-person reminders to wear them So an increase of 13% masking to 42% masking led to an 11% effective drop in COVID19 spread. So even though 70% of people weren't affected (either the 13% who wore a mask anyway, or the 60% of people who ignored the mask advice), you still had a measurable decrease in COVID19 spread. Which means masking mandates / masking propaganda works. Even with the huge number of people who ignore it, its still an effective means to cut down on COVID19 spread.
- slg 5y ago
exabrial 5y ago
This is truly great news, as we've need some controlled studies. However, _mandates_, literally threatening people with police violence, bodily or financial harm, is not the correct way forward. I think the best solution is improved mandates for airflow. It's a lot easier to improve airflow in a building than it is to police and enforce a mask mandate.
- douglasisshiny 5y ago
  >However, _mandates_, literally threatening people with police violence, bodily or financial harm, is not the correct way forward. Maybe I'm missing something, but is this actually a thing? Who in the mainstream proposing police violence, bodily or financial harm? The worst I've heard (in the U.S.) is that a business may not allow you to enter if you're not wearing a mask, which is well within their right and reasonable.
  - logicalmonster 5y ago
    > Who in the mainstream proposing police violence, bodily or financial harm? People with some flavor of libertarian viewpoint have often explained how every piece of legislation is ultimately backed up by physical force from police officers. Ultimately, if you violate any government policy: whether it is taxation, opening up an illegal lemonade stand, or trying to attend a restaurant that has a vaccine mandate imposed on it, it is ultimately physical force that backs this up if compliance is refused. As far as financial harm: see the government strongly encouraging corporations to mandate vaccines or other similar policies.
  - learc83 5y ago
    Libertarians like to make this argument about any government enforcement action. If the government tells you that you can't play loud music after 10pm and you do it anyway, eventually someone will issue you a citation. If you refuse to pay that, eventually you'll get a court summons. If you fail to appear, eventually a police officer may arrest you. If you resist, they will use force to make you comply. It's a bit hyperbolic, but it is a standard libertarian/objectivist "gotcha".
lol1lol 5y ago
alternate hypothesis is statistically insignificant. with a 300k sample size a p-value 0.04. damn.
deleted 5y ago
[deleted]
cfn 5y ago
Here is the paper (or one of them, it is not clear after so many links): https://www.poverty-action.org/sites/default/files/publications/Mask_RCT____Symptomatic_Seropositivity_083121.pdf https://www.poverty-action.org/sites/default/files/publicati... Bottom line: "The proportion of individuals with COVID-like symptoms was 7.62% (N=13,273) in the intervention arm and 8.62% (N=13,893) in the control arm. Blood samples were collected from N=10,952 consenting, symptomatic individuals. Adjusting for baseline covariates, the 2 intervention reduced symptomatic seroprevalence by 9.3% (adjusted prevalence ratio (aPR) = 0.91 [0.82, 1.00]; control prevalence 0.76%; treatment prevalence 0.68%). In villages randomized to surgical masks (n = 200), the relative reduction was 11.2% overall (aPR = 0.89 [0.78, 1.00]) and 34.7% among individuals 60+ (aPR = 0.65 [0.46, 0.85]). No adverse events were reported."
- treis 5y ago
  This is a pretty modest impact, a short duration, and is somewhat clouded by it not being a double blind study. The rate of infection at 7.62% vs 8.62% are particularly troublesome. As a comparison, it's estimated that 1/3-1/2 of Americans have been infected with Covid. It's an open question of what the end game would be. Could be that both groups would end at the same infection rate. The masked group might just take longer to get there.
  - numbsafari 5y ago
    > The masked group might just take longer to get there. That's not a bad thing. Remember "flatten the curve"? Avoiding everyone from getting it isn't the goal. Preventing the collapse of the healthcare system is.
    - gotoeleven 5y ago
      We are now into month 17 of two weeks to flatten the curve. Even in the height of the initial wave hospitals were mostly not overwhelmed. Remember the field hospitals and hospital ships that sat empty in New York City?
GeekyBear 5y ago
Cloth masks are quite effective against viruses with a droplet based spread. Widespread mask use came as close to wiping out last year's Flu season as we've ever seen. >Amid COVID-19 pandemic, flu has disappeared in the US NEW YORK (AP) — February is usually the peak of flu season, with doctors’ offices and hospitals packed with suffering patients. But not this year. Nationally, “this is the lowest flu season we’ve had on record,” according to a surveillance system that is about 25 years old, said Lynnette Brammer of the U.S. Centers for Disease Control and Prevention. https://apnews.com/article/flu-has-disappeared-us-pandemic-2145d999319b53d8a32a829a324f398d https://apnews.com/article/flu-has-disappeared-us-pandemic-2... However, during the same period where the Flu disappeared, there was a massive Covid surge, because cloth masks are not an effective means of filtering an airborne virus from the air you breathe. Here's one of the scientists on President Biden's Covid advisory board being interviewed on PBS. >Studies that have been done show that if an individual might get infected within 15 minutes in a room, by time and concentration of the virus in the room, add a face cloth covering you only get about five more minutes of protection. On the other hand if you use the n95 respirators and fit them tight to your face, you can actually spend 25 hours in that same room and still be protected. https://www.pbs.org/wnet/amanpour-and-company/video/do-masks-provide-much-protection-we-think-bglhwy/ https://www.pbs.org/wnet/amanpour-and-company/video/do-masks... To get the kind of protection people imagine that cloth masks provide, you have to wear the same sort of masks that medical professionals are required to wear while treating patients who have an airborne virus. Which is not surprising since we know Covid is fully airborne. Unfortunately, those of us on the left have rejected this news in the same way that the crowd at a Trump rally rejected Trump when he told them that they should get vaccinated. Cloth masks are not an adequate substitute for vaccination, especially for children too young to be vaccinated who are now expected to attend full school days.
- Kiro 5y ago
  Flu was almost eliminated in Sweden as well and we had almost no mask usage. Feels like social distancing was the more important factor.
  - GeekyBear 5y ago
starik36 5y ago
So am I understanding the study correctly? > Those living in villages randomly assigned to a series of interventions promoting the use of surgical masks were about 11% less likely than those living in control villages to develop COVID-19 The surgical masks are 11% more effective in preventing COVID infection than not wearing masks at all?
- rafaelero 5y ago
  No, you are not interpreting it correctly. The 11% reduction is the effect of the intervention (encouraging people to use masks), which meant that the rate of people complying with the measure went from 12% (control) to 42% (intervention). The 11% refers to the effect of increasing mask use by that magnitude.
  - mdp2021 5y ago
    So, having roughly one third of the population wear the mask reduced symptomatic infection of roughly a dozen percent. Can one suppose that an almost fully compliant population would see a reduction of symptomatic infections of roughly one third - or am I missing something? Can this study suggest that a compliant population should see roughly one third less infections? Edit: for example, the study lasted, I understand, only a couple of months: so, will this timeframe be enough to suppose that the exponential effects can be taken into account, and that the reduction in the infections should be more than just tripled, if one supposed almost full compliance?
- aw1621107 5y ago
  Not quite. The wording has to be parsed carefully: > Those living in villages randomly assigned to a series of interventions promoting the use of surgical masks were about 11% less likely than those living in control villages to develop COVID-19 So it's not mask vs. maskless; it's promotion of masks vs. no such promotion. The study [0] gives more information: > In villages that received the intervention, mask use increased by 29 percentage points (from 13 percent in the comparison villages to 42 percent in treatment villages). [0]: https://www.poverty-action.org/study/impact-mask-distribution-and-promotion-mask-uptake-and-covid-19-bangladesh https://www.poverty-action.org/study/impact-mask-distributio...
endisneigh 5y ago
without controlling for average time spent at various distances it seems hard to get any conclusion from this. if wearing a mask results in people staying away from you, is the mask effective, or is distance effective?
theiz 5y ago
Quite convinced we have to prepare on getting infected some time. Covid will be around for the coming years and years. Nice that you have less chance of getting that, and then what? You can’t walk around with a mask indefinitely. Saw another report this week that links to the viral load and the impact: low viral load = no symptoms, no immunity. Medium viral load is minimal symptoms, Immunization. High viral load = serious illness (and immunity, but potentially also hospitalisation and/or long covid) Would be nice if the masks help you to get in the sweet spot.
- Volundr 5y ago
  > You can’t walk around with a mask indefinitely. I want to be clear I'm not advocating for this, but you can't? Why not? What's the time limit?
  - proc0 5y ago
    Why not lockdown forever, and everyone social distance and isolate? We CAN do that right?
    - Volundr 5y ago
      > Why not lockdown forever, and everyone social distance and isolate? We CAN do that right? Can we? I mean a lock down has economic consequences that I just don't see from mask use. Maybe technically it's possible, but one of these things is not like the other. I'm not advocating for permanent mask use. I'm not even advocating particularly hard for mask use in general right now (I mean we probably should). I'm not advocating for mandates. But I keep seeing mask use being presented as some great hardship, that can only be born briefly (if at all) and I just don't see it.
      - proc0 5y ago
        I'm not really arguing in favor of it... the point was we shouldn't just do something permanently because it reduces risk and it's possible. It's absolutely possible to adapt everyone into long term lockdowns, and I believe parts of Australia are in this right now, but we can clearly see that it is a bad idea. > But I keep seeing mask use being presented as some great hardship, that can only be born briefly (if at all) and I just don't see it. In my opinion, it's not being done consistently in a way that makes sense. It's at best a lazy rule to make everyone behave the same way. Not everyone is spreading the virus, so it follows not everyone should wear one, yet there are zero attempts at factoring this in to mandates. It's everyone regardless of health. Again, at best it's a lazy implementation that enables authorities to do blanket power grabs instead of creative solutions that work not just for the vulnerable but also the majority of people who are already protected in some way.
mhb 5y ago
Why didn't they test N95 masks?
- GeekyBear 5y ago
  >Why didn't they test N95 masks? The difference between a cloth mask and an n95 mask when dealing with an airborne virus has been tested. >Studies that have been done show that if an individual might get infected within 15 minutes in a room, by time and concentration of the virus in the room, add a face cloth covering you only get about five more minutes of protection. On the other hand if you use the n95 respirators and fit them tight to your face, you can actually spend 25 hours in that same room and still be protected. https://www.pbs.org/wnet/amanpour-and-company/video/do-masks-provide-much-protection-we-think-bglhwy/ https://www.pbs.org/wnet/amanpour-and-company/video/do-masks...
fasteddie31003 5y ago
I was militant pro-mask when I was unvaccinated. Now that I'm vaccinated and have no comorbidities, I'm OK with being exposed to COVID-19. In fact, I want to have a mild case of COVID-19 to get natural immunity. Natural immunity seems to be more effective than the vaccine for long lasting immunity.
- nabakin 5y ago
  Do you have a good source on this?
  - fasteddie31003 5y ago
    https://www.science.org/content/article/having-sars-cov-2-once-confers-much-greater-immunity-vaccine-vaccination-remains-vital https://www.science.org/content/article/having-sars-cov-2-on...
  - gbjw 5y ago
    https://www.science.org/content/article/having-sars-cov-2-once-confers-much-greater-immunity-vaccine-vaccination-remains-vital https://www.science.org/content/article/having-sars-cov-2-on...
- Scoundreller 5y ago
  I’m not quite at that point of “fuck it, I’m vaccinated, come at me”, but I have to travel soon and the country I’m transiting through (Iceland) now requires a test. I’m nervous about it because I’m vaccinated, so I very well could have a mild infection and not know it, and get denied boarding and quarantined at home. At least it’s an antigen test and those miss most non-symptomatic infection anyway.
  - blub 5y ago
    Or you could test yourself daily at home before your departure day and remove the element of surprise.
    - 5y ago
bendbro 5y ago
Does the paper reveal the seroprevalence by control village and intervention village? I just scanned it and can find no such information. EDIT: Table A14 is the closest I can find but it is only coefficients, not the underlying counts.
- nradov 5y ago
  This study didn't perform seroprevalence sampling.
  - bendbro 5y ago
    It did: "Blood samples were collected from N=10,952 consenting, symptomatic individuals." From https://www.poverty-action.org/sites/default/files/publications/Mask_RCT____Symptomatic_Seropositivity_083121.pdf https://www.poverty-action.org/sites/default/files/publicati... , pg 2, Abstract section, para 2
    - nradov 5y ago
      No that wasn't sampling in the sense that you asked the original question. They only tested symptomatic individuals. They didn't test representative random samples of the intervention and control groups.
aaomidi 5y ago
How about when the surgical masks get reused?
bgorman 5y ago
The problem with this mask business is it treats masks as the only variable. The United States is incredibly unhealthy and most people do not get enough exercise or spend enough time outdoors. It would not surprise me if governments would obtain better results by telling citizens to exercise regularly and eat healthy. Instead it seems like governments are doubling down on a strategy on scaring/bullying out of shape citizens into staying at home afraid. The most rediculous policy of all is governments requiring masks for outdoor exercise. 11% is frankly not going to move the needle. I could probably reduce my chance of dying in a vehicle accident by way over 11% by refusing to ride bicycles. It simply isn’t meaningful.
- nradov 5y ago
  Maintaining the recommended level of physical activity cuts COVID-19 death risk by 4× compared to being sedentary. https://bjsm.bmj.com/content/early/2021/07/21/bjsports-2021-104203 https://bjsm.bmj.com/content/early/2021/07/21/bjsports-2021-... And before anyone claims that it's just a correlation, please read the whole paper. The authors did a good job of establishing causality.
  - mdp2021 5y ago
    > cuts COVID-19 death risk by 4× And halved severe illness.
- mdp2021 5y ago
  No, the study is about a ~11% decrease of infections after a ~30% increase of mask use after an awareness campaign. > masks for outdoor exercise I really hope that is for the jogging in the market area of Delhi (I hope this was at least in urban areas).
iandanforth 5y ago
Things I wish everyone knew and acted on: 1. Masks reduce spread (this study) 2. Covid-19 is an airborne disease and primarily spread through aerosols 3. Being in a poorly ventilated space (even if everyone is masked) with an infected person means a significant chance of being infected. 4. While (1) is true for even meh-masks, to prevent infection in (3), you need to be wearing a tight-fitting high quality mask. No beards, no cloth, no surgical. N-95 or better with total seal.
nradov 5y ago
What people seem to be missing is that this study only covered a limited period. While surgical masks can slightly reduce the risk of contagion for individual interactions, over a longer period all of us will eventually be exposed regardless of what precautions we take. The virus isn't going away. Think of it like a soccer goalie defending against an endless series of penalty kicks. He might block the first few balls but eventually one will get through. https://www.businessinsider.com/delta-variant-made-herd-immunity-not-possible-astrazeneca-developer-2021-8 https://www.businessinsider.com/delta-variant-made-herd-immu... This is why it's so important for people who haven't yet been infected to get vaccinated. And take other steps to strengthen your immune system such as reducing obesity, maintaining adequate vitamin D levels, and engaging in the recommended level of physical activity. https://www.cnbc.com/2021/03/08/covid-cdc-study-finds-roughly-78percent-of-people-hospitalized-were-overweight-or-obese.html https://www.cnbc.com/2021/03/08/covid-cdc-study-finds-roughl... https://vitamin-d-covid.shotwell.ca/ https://vitamin-d-covid.shotwell.ca/ https://bjsm.bmj.com/content/early/2021/07/21/bjsports-2021-104203 https://bjsm.bmj.com/content/early/2021/07/21/bjsports-2021-...
mrfusion 5y ago
If a study found the opposite, would we be hearing about it?
belorn 5y ago
Its interesting that the article do not mention a rather interesting finding in the study. For the age groups of < 50 years the effect was not statistically significant with the control and the mask wearing villages having similar rate of covid-19. Why aren't masks effective to reduce the spread for that age group? The discussion part of the study don't explore it. Is the distancing behavior of people aged 50 or higher different than those below? I would like to see further studies being done on the younger demographic in order to explain why the data is looking like it is.
- jasonlaramburu 5y ago
  Maybe lower mask adherence among younger people or different behaviors-- older people in villages might stay at home more.
  - packetlost 5y ago
    if the latter is true, then wouldn't that be an indicator that masks do not, in fact, work as well as thought?
    - jasonlaramburu 5y ago
      It could, or it could mean that the protective effect of surgical masks is most pronounced indoors.
- jacquesm 5y ago
  Compliance.
- hncurious 5y ago
  They did report that physical distancing increased in villages that were given masks, so that may explain it. Unfortunately they didn't untangle that effect? How do we know to what degree it was the masks vs increased distancing?
- mywittyname 5y ago
  > Why aren't masks effective to reduce the spread for that age group? This is a good question and I think it is an important one since the title implies a different situation than what was actually tested. So the 11% reduction was due to an effort to increase mask wearing compliance by means of... > Providing free masks, informing people about the importance of covering both the mouth and nose, reminding people in-person when they were unmasked in public, and role-modeling by community leaders It's probably not that masks are less effective on people under 50, but that the information campaign was less effective at influencing that group to wear their masks. Also, the results are interesting: > The observers found that just over 13% of people in the villages that received no interventions wore a mask properly, compared with more than 42% of people in the villages where each household received free masks and in-person reminders to wear them. It seems that there is much more progress that can be made in getting people to wear masks. And we still don't know how effective 95%+ compliance will be at reducing the spread. Finally, the report does note that villages provided with cloth masks had worse outcomes than those who were provided with surgical masks.
alecst 5y ago
My first reaction was to consider this as pretty damning of mass use. But when I considered it more I don't think the study is as damning of masks as it is of mask mandates. The problem is only ~30% more people wore masks in the intervention arm of the study. So the best possible outcome, removing 30% from the infection group entirely (essentially taking them out of the population -- a "perfect spherical mask" approximation), is a 30% reduction in cases. Which is substantial, but no one expects masks to be that effective anyway. 11% seems a reasonable ballpark. If everyone had worn masks it would have been easier to measure the effect of just the masks. Still, it's worth considering the big picture. If mask mandates aren't enforced, they're not worth a whole lot. Especially if you have limited political capital to spend.
- pseudalopex 5y ago
  The interventions the article mentioned did not include a mandate.
  - alecst 5y ago
    Yea true, more like encouraging people to wear masks.
nikolay 5y ago
Reduce but not by much. One could buy KN95 masks at comparable costs and wear them longer and be safer. Not sure why people would get a surgical mask. Governments must subsidize quality masks!
fulafel 5y ago
Is to possible to measure or control for behavioral, vs direct transmission blocking, effects of masks? If they seem more effective for old people, could it be that they help remind people about the ongoing pandemic and infection risk, and signal that mask wearers prefer to keep distance to others.
incrudible 5y ago
TLDR; ARR/month estimate: Lower bound: 2.86E-05 Mid-range: 8.91E-05 Upper-Bound: 1.50E-04 That's on page 90.
BobJackienine 5y ago
It wasn't the mask wearing it was the distancing when I was in the military mission oriented personal protection taught us never to issue surgical masks when they're touched they're contaminated and need to be thrown out. ITT: either this place is turned into Reddit with a bunch of retards bots or none of you can read statistics or can even do basic math.

152 points by djrogers 5y ago

> The researchers enrolled nearly 350,000 people from 600 villages in rural Bangladesh Wow. I was about to complain about "small n", but... an experiment of this size is not small at all. Congrats on the researchers on doing such a big study!

cfn 5y ago
I think it is a bit cheeky of them. They promoted the usage of masks and distancing in 600 villages totalling 350,000 people and observed the results (mask wearing plus distancing) in mosques (by sampling, not by checking each individual).
- jerf 5y ago
  I know it's easy to get cynical about "sampling" when you see a stream of studies sampling populations of millions with n = 12 and getting p values just barely considered "significant", but that's not the fault of "sampling". That's just... gathering no data, basically, or if you prefer, going through the motions of gathering data without actually doing it.
  - cfn 5y ago
    I am not arguing with the method, I only think the language of the paper is misleading to the point that the parent commenter aparently thinks they actually analysed hundred of thousands of subjects when they just extrapolated their observations to that number. It may even be right and significant but that is not my point.
    - dragontamer 5y ago
      I've reread the article + paper with your discussion in mind, and I agree with you. It seems misleading, and I failed to understand the study from the headline / abstract. Its not a "bad" study per se, but its definitely entering clickbait. I'm still happy they conducted the study and presented their research.
kragen 5y ago
Maybe the relevant point is that it needed to be this big to get a P-value of less than .05, since they only got .04 even with 350,000 people. This is dramatically less effectiveness than I was expecting when I was pushing for mask mandates last year, and within a few months it was obvious that masks alone weren't having the large effect I had hoped for. Now we have quantitative estimates of how small the effect was (disappointingly small) and when it worked (cloth masks had almost no effect).
- dragontamer 5y ago
  When 70% of people weren't affected by the experiment (13% were wearing masks before the experiment started. 60% of people didn't wear a mask after the experiment), then of course the numbers are going to be small. Seeing a measurable difference when the population only changed from 13% mask to 40%ish mask usage is pretty outstanding IMO.
  - kragen 5y ago
    I don't think that's correct; see https://news.ycombinator.com/item?id=28407881 https://news.ycombinator.com/item?id=28407881 for the argument in more detail.
    - dragontamer 5y ago
      My argument and your argument are seemingly unrelated. That means that the full matrix of situations are available: I'm correct and you're correct. I'm correct and you're wrong. I'm wrong and you're correct, and finally I'm wrong and you're wrong. ---------- So lets just try again from the top. The study shows that an 8-week mask-awareness campaign in Bangladesh across 300 villages (+300 "control" villages 2+km away where mask-awareness did NOT happen) leads to a 29% increase in mask usage and an 11% decrease in COVID19 cases. Is there anything wrong with this new, revised statement I made? It seems to be the big "A / B" test that everyone's wanted for mask studies.
      - kragen 5y ago
otabdeveloper4 5y ago
Size of N isn't the issue, controlling for confounding variables is.

ch4s3 5y ago

> There were significantly fewer COVID-19 cases in villages with surgical masks compared with the control villages. (Although there were also fewer COVID-19 cases in villages with cloth masks as compared to control villages, the difference was not statistically significant.) This aligns with lab tests showing that surgical masks have better filtration than cloth masks. However, cloth masks did reduce the overall likelihood of experiencing symptoms of respiratory illness during the study period. I think this is probably the most interesting part, and worth watching in future studies.

majormajor 5y ago
It's surprising to me that cloth masks can't even do the 11% of surgical masks. Which isn't much, but surgical masks are non-optimal for many reasons. Not to mention that this doesn't seem the same as "while wearing a surgical mask you only get 11% increase in protection" but is a population-level thing. There was still non-compliance that presumably lowered the efficacy. I would've intuitively guessed that the better fit of cloth masks would make them better, but presumably the mask surface of a surgical mask has properties that offset that? Would be great to see numbers for N95 masks. Intuitively I'd assume they'd be much more effective as they have better fit + higher filtration, but of course, confirmation would be great. Fits with what we're seeing in Europe such as airlines banning cloth masks, though. The great incoherent idiocy of anti-* Americans on the issue of masks has always been that they say "cloth masks are ineffective" and propose a solution of "do nothing" instead of "get effective masks."
- slg 5y ago
  >It's surprising to me that cloth masks can't even do the 11% of surgical masks. Just want to add clarification here. The 11% number is the community impact of the programs designed to increase mask usage. It is not the effectiveness of a mask on an individual level. That number will be much higher since as you said a number of people didn't/don't comply at a societal level.
  - majormajor 5y ago

chitowneats 5y ago

From Martin Kulldorff, esteemed (though contrarian) Harvard Med epidemiologist: "Odd that mask advocates are excited by this study. As a vaccine advocate, I would be horrified if a vaccine trial showed 11% efficacy. Based on the 95% confidence intervals, we do not even know if surgical mask efficacy is more than 0%." https://twitter.com/MartinKulldorff/status/1433202651106201607?s=20 https://twitter.com/MartinKulldorff/status/14332026511062016...

SubiculumCode 5y ago
I think this thread is a decent refutation that the CI lower bound was at 0: "First, the 11% reduction comes from a 30% increase in mask-use. The IV estimate (naively scaling things linearly) would thus be more like a 37% reduction in COVID from going from zero to universal masking." "Second, we find much larger effects among the elderly (a 35% reduction among 60+ without the above scaling). This suggests that the total reduction in morbidity and mortality from universal masking may be considerably larger than even the 37% number, perhaps more than 50%." "Third, it's not quite an apples to apples comparison because we are estimating the community impact of masks, whereas the vaccine studies only isolate the individual protective effect. The efficacy of vaccines at the population level may be larger than trials imply." https://twitter.com/Jabaluck/status/1433129444940599296 https://twitter.com/Jabaluck/status/1433129444940599296
dragontamer 5y ago
EDIT: Woops, read wrong. Lemme post the quote instead. > The observers found that just over 13% of people in the villages that received no interventions wore a mask properly, compared with more than 42% of people in the villages where each household received free masks and in-person reminders to wear them So an increase of 13% masking to 42% masking led to an 11% effective drop in COVID19 spread. So even though 70% of people weren't affected (either the 13% who wore a mask anyway, or the 60% of people who ignored the mask advice), you still had a measurable decrease in COVID19 spread. Which means masking mandates / masking propaganda works. Even with the huge number of people who ignore it, its still an effective means to cut down on COVID19 spread.
slg 5y ago

exabrial 5y ago

This is truly great news, as we've need some controlled studies. However, _mandates_, literally threatening people with police violence, bodily or financial harm, is not the correct way forward. I think the best solution is improved mandates for airflow. It's a lot easier to improve airflow in a building than it is to police and enforce a mask mandate.

douglasisshiny 5y ago
>However, _mandates_, literally threatening people with police violence, bodily or financial harm, is not the correct way forward. Maybe I'm missing something, but is this actually a thing? Who in the mainstream proposing police violence, bodily or financial harm? The worst I've heard (in the U.S.) is that a business may not allow you to enter if you're not wearing a mask, which is well within their right and reasonable.
- logicalmonster 5y ago
  > Who in the mainstream proposing police violence, bodily or financial harm? People with some flavor of libertarian viewpoint have often explained how every piece of legislation is ultimately backed up by physical force from police officers. Ultimately, if you violate any government policy: whether it is taxation, opening up an illegal lemonade stand, or trying to attend a restaurant that has a vaccine mandate imposed on it, it is ultimately physical force that backs this up if compliance is refused. As far as financial harm: see the government strongly encouraging corporations to mandate vaccines or other similar policies.
- learc83 5y ago
  Libertarians like to make this argument about any government enforcement action. If the government tells you that you can't play loud music after 10pm and you do it anyway, eventually someone will issue you a citation. If you refuse to pay that, eventually you'll get a court summons. If you fail to appear, eventually a police officer may arrest you. If you resist, they will use force to make you comply. It's a bit hyperbolic, but it is a standard libertarian/objectivist "gotcha".

lol1lol 5y ago

alternate hypothesis is statistically insignificant. with a 300k sample size a p-value 0.04. damn.

deleted 5y ago

[deleted]

cfn 5y ago

Here is the paper (or one of them, it is not clear after so many links): https://www.poverty-action.org/sites/default/files/publications/Mask_RCT____Symptomatic_Seropositivity_083121.pdf https://www.poverty-action.org/sites/default/files/publicati... Bottom line: "The proportion of individuals with COVID-like symptoms was 7.62% (N=13,273) in the intervention arm and 8.62% (N=13,893) in the control arm. Blood samples were collected from N=10,952 consenting, symptomatic individuals. Adjusting for baseline covariates, the 2 intervention reduced symptomatic seroprevalence by 9.3% (adjusted prevalence ratio (aPR) = 0.91 [0.82, 1.00]; control prevalence 0.76%; treatment prevalence 0.68%). In villages randomized to surgical masks (n = 200), the relative reduction was 11.2% overall (aPR = 0.89 [0.78, 1.00]) and 34.7% among individuals 60+ (aPR = 0.65 [0.46, 0.85]). No adverse events were reported."

treis 5y ago
This is a pretty modest impact, a short duration, and is somewhat clouded by it not being a double blind study. The rate of infection at 7.62% vs 8.62% are particularly troublesome. As a comparison, it's estimated that 1/3-1/2 of Americans have been infected with Covid. It's an open question of what the end game would be. Could be that both groups would end at the same infection rate. The masked group might just take longer to get there.
- numbsafari 5y ago
  > The masked group might just take longer to get there. That's not a bad thing. Remember "flatten the curve"? Avoiding everyone from getting it isn't the goal. Preventing the collapse of the healthcare system is.
  - gotoeleven 5y ago
    We are now into month 17 of two weeks to flatten the curve. Even in the height of the initial wave hospitals were mostly not overwhelmed. Remember the field hospitals and hospital ships that sat empty in New York City?

GeekyBear 5y ago

Cloth masks are quite effective against viruses with a droplet based spread. Widespread mask use came as close to wiping out last year's Flu season as we've ever seen. >Amid COVID-19 pandemic, flu has disappeared in the US NEW YORK (AP) — February is usually the peak of flu season, with doctors’ offices and hospitals packed with suffering patients. But not this year. Nationally, “this is the lowest flu season we’ve had on record,” according to a surveillance system that is about 25 years old, said Lynnette Brammer of the U.S. Centers for Disease Control and Prevention. https://apnews.com/article/flu-has-disappeared-us-pandemic-2145d999319b53d8a32a829a324f398d https://apnews.com/article/flu-has-disappeared-us-pandemic-2... However, during the same period where the Flu disappeared, there was a massive Covid surge, because cloth masks are not an effective means of filtering an airborne virus from the air you breathe. Here's one of the scientists on President Biden's Covid advisory board being interviewed on PBS. >Studies that have been done show that if an individual might get infected within 15 minutes in a room, by time and concentration of the virus in the room, add a face cloth covering you only get about five more minutes of protection. On the other hand if you use the n95 respirators and fit them tight to your face, you can actually spend 25 hours in that same room and still be protected. https://www.pbs.org/wnet/amanpour-and-company/video/do-masks-provide-much-protection-we-think-bglhwy/ https://www.pbs.org/wnet/amanpour-and-company/video/do-masks... To get the kind of protection people imagine that cloth masks provide, you have to wear the same sort of masks that medical professionals are required to wear while treating patients who have an airborne virus. Which is not surprising since we know Covid is fully airborne. Unfortunately, those of us on the left have rejected this news in the same way that the crowd at a Trump rally rejected Trump when he told them that they should get vaccinated. Cloth masks are not an adequate substitute for vaccination, especially for children too young to be vaccinated who are now expected to attend full school days.

Kiro 5y ago
Flu was almost eliminated in Sweden as well and we had almost no mask usage. Feels like social distancing was the more important factor.
- GeekyBear 5y ago

starik36 5y ago

So am I understanding the study correctly? > Those living in villages randomly assigned to a series of interventions promoting the use of surgical masks were about 11% less likely than those living in control villages to develop COVID-19 The surgical masks are 11% more effective in preventing COVID infection than not wearing masks at all?

rafaelero 5y ago
No, you are not interpreting it correctly. The 11% reduction is the effect of the intervention (encouraging people to use masks), which meant that the rate of people complying with the measure went from 12% (control) to 42% (intervention). The 11% refers to the effect of increasing mask use by that magnitude.
- mdp2021 5y ago
  So, having roughly one third of the population wear the mask reduced symptomatic infection of roughly a dozen percent. Can one suppose that an almost fully compliant population would see a reduction of symptomatic infections of roughly one third - or am I missing something? Can this study suggest that a compliant population should see roughly one third less infections? Edit: for example, the study lasted, I understand, only a couple of months: so, will this timeframe be enough to suppose that the exponential effects can be taken into account, and that the reduction in the infections should be more than just tripled, if one supposed almost full compliance?
aw1621107 5y ago
Not quite. The wording has to be parsed carefully: > Those living in villages randomly assigned to a series of interventions promoting the use of surgical masks were about 11% less likely than those living in control villages to develop COVID-19 So it's not mask vs. maskless; it's promotion of masks vs. no such promotion. The study [0] gives more information: > In villages that received the intervention, mask use increased by 29 percentage points (from 13 percent in the comparison villages to 42 percent in treatment villages). [0]: https://www.poverty-action.org/study/impact-mask-distribution-and-promotion-mask-uptake-and-covid-19-bangladesh https://www.poverty-action.org/study/impact-mask-distributio...

endisneigh 5y ago

without controlling for average time spent at various distances it seems hard to get any conclusion from this. if wearing a mask results in people staying away from you, is the mask effective, or is distance effective?

theiz 5y ago

Quite convinced we have to prepare on getting infected some time. Covid will be around for the coming years and years. Nice that you have less chance of getting that, and then what? You can’t walk around with a mask indefinitely. Saw another report this week that links to the viral load and the impact: low viral load = no symptoms, no immunity. Medium viral load is minimal symptoms, Immunization. High viral load = serious illness (and immunity, but potentially also hospitalisation and/or long covid) Would be nice if the masks help you to get in the sweet spot.

Volundr 5y ago
> You can’t walk around with a mask indefinitely. I want to be clear I'm not advocating for this, but you can't? Why not? What's the time limit?
- proc0 5y ago
  Why not lockdown forever, and everyone social distance and isolate? We CAN do that right?
  - Volundr 5y ago
    > Why not lockdown forever, and everyone social distance and isolate? We CAN do that right? Can we? I mean a lock down has economic consequences that I just don't see from mask use. Maybe technically it's possible, but one of these things is not like the other. I'm not advocating for permanent mask use. I'm not even advocating particularly hard for mask use in general right now (I mean we probably should). I'm not advocating for mandates. But I keep seeing mask use being presented as some great hardship, that can only be born briefly (if at all) and I just don't see it.
    - proc0 5y ago
      I'm not really arguing in favor of it... the point was we shouldn't just do something permanently because it reduces risk and it's possible. It's absolutely possible to adapt everyone into long term lockdowns, and I believe parts of Australia are in this right now, but we can clearly see that it is a bad idea. > But I keep seeing mask use being presented as some great hardship, that can only be born briefly (if at all) and I just don't see it. In my opinion, it's not being done consistently in a way that makes sense. It's at best a lazy rule to make everyone behave the same way. Not everyone is spreading the virus, so it follows not everyone should wear one, yet there are zero attempts at factoring this in to mandates. It's everyone regardless of health. Again, at best it's a lazy implementation that enables authorities to do blanket power grabs instead of creative solutions that work not just for the vulnerable but also the majority of people who are already protected in some way.

mhb 5y ago

Why didn't they test N95 masks?

GeekyBear 5y ago
>Why didn't they test N95 masks? The difference between a cloth mask and an n95 mask when dealing with an airborne virus has been tested. >Studies that have been done show that if an individual might get infected within 15 minutes in a room, by time and concentration of the virus in the room, add a face cloth covering you only get about five more minutes of protection. On the other hand if you use the n95 respirators and fit them tight to your face, you can actually spend 25 hours in that same room and still be protected. https://www.pbs.org/wnet/amanpour-and-company/video/do-masks-provide-much-protection-we-think-bglhwy/ https://www.pbs.org/wnet/amanpour-and-company/video/do-masks...

fasteddie31003 5y ago

I was militant pro-mask when I was unvaccinated. Now that I'm vaccinated and have no comorbidities, I'm OK with being exposed to COVID-19. In fact, I want to have a mild case of COVID-19 to get natural immunity. Natural immunity seems to be more effective than the vaccine for long lasting immunity.

nabakin 5y ago
Do you have a good source on this?
- fasteddie31003 5y ago
  https://www.science.org/content/article/having-sars-cov-2-once-confers-much-greater-immunity-vaccine-vaccination-remains-vital https://www.science.org/content/article/having-sars-cov-2-on...
- gbjw 5y ago
  https://www.science.org/content/article/having-sars-cov-2-once-confers-much-greater-immunity-vaccine-vaccination-remains-vital https://www.science.org/content/article/having-sars-cov-2-on...
Scoundreller 5y ago
I’m not quite at that point of “fuck it, I’m vaccinated, come at me”, but I have to travel soon and the country I’m transiting through (Iceland) now requires a test. I’m nervous about it because I’m vaccinated, so I very well could have a mild infection and not know it, and get denied boarding and quarantined at home. At least it’s an antigen test and those miss most non-symptomatic infection anyway.
- blub 5y ago
  Or you could test yourself daily at home before your departure day and remove the element of surprise.
  - 5y ago

bendbro 5y ago

Does the paper reveal the seroprevalence by control village and intervention village? I just scanned it and can find no such information. EDIT: Table A14 is the closest I can find but it is only coefficients, not the underlying counts.

nradov 5y ago
This study didn't perform seroprevalence sampling.
- bendbro 5y ago
  It did: "Blood samples were collected from N=10,952 consenting, symptomatic individuals." From https://www.poverty-action.org/sites/default/files/publications/Mask_RCT____Symptomatic_Seropositivity_083121.pdf https://www.poverty-action.org/sites/default/files/publicati... , pg 2, Abstract section, para 2
  - nradov 5y ago
    No that wasn't sampling in the sense that you asked the original question. They only tested symptomatic individuals. They didn't test representative random samples of the intervention and control groups.

aaomidi 5y ago

How about when the surgical masks get reused?

bgorman 5y ago

The problem with this mask business is it treats masks as the only variable. The United States is incredibly unhealthy and most people do not get enough exercise or spend enough time outdoors. It would not surprise me if governments would obtain better results by telling citizens to exercise regularly and eat healthy. Instead it seems like governments are doubling down on a strategy on scaring/bullying out of shape citizens into staying at home afraid. The most rediculous policy of all is governments requiring masks for outdoor exercise. 11% is frankly not going to move the needle. I could probably reduce my chance of dying in a vehicle accident by way over 11% by refusing to ride bicycles. It simply isn’t meaningful.

nradov 5y ago
Maintaining the recommended level of physical activity cuts COVID-19 death risk by 4× compared to being sedentary. https://bjsm.bmj.com/content/early/2021/07/21/bjsports-2021-104203 https://bjsm.bmj.com/content/early/2021/07/21/bjsports-2021-... And before anyone claims that it's just a correlation, please read the whole paper. The authors did a good job of establishing causality.
- mdp2021 5y ago
  > cuts COVID-19 death risk by 4× And halved severe illness.
mdp2021 5y ago
No, the study is about a ~11% decrease of infections after a ~30% increase of mask use after an awareness campaign. > masks for outdoor exercise I really hope that is for the jogging in the market area of Delhi (I hope this was at least in urban areas).

iandanforth 5y ago

Things I wish everyone knew and acted on: 1. Masks reduce spread (this study) 2. Covid-19 is an airborne disease and primarily spread through aerosols 3. Being in a poorly ventilated space (even if everyone is masked) with an infected person means a significant chance of being infected. 4. While (1) is true for even meh-masks, to prevent infection in (3), you need to be wearing a tight-fitting high quality mask. No beards, no cloth, no surgical. N-95 or better with total seal.

nradov 5y ago

What people seem to be missing is that this study only covered a limited period. While surgical masks can slightly reduce the risk of contagion for individual interactions, over a longer period all of us will eventually be exposed regardless of what precautions we take. The virus isn't going away. Think of it like a soccer goalie defending against an endless series of penalty kicks. He might block the first few balls but eventually one will get through. https://www.businessinsider.com/delta-variant-made-herd-immunity-not-possible-astrazeneca-developer-2021-8 https://www.businessinsider.com/delta-variant-made-herd-immu... This is why it's so important for people who haven't yet been infected to get vaccinated. And take other steps to strengthen your immune system such as reducing obesity, maintaining adequate vitamin D levels, and engaging in the recommended level of physical activity. https://www.cnbc.com/2021/03/08/covid-cdc-study-finds-roughly-78percent-of-people-hospitalized-were-overweight-or-obese.html https://www.cnbc.com/2021/03/08/covid-cdc-study-finds-roughl... https://vitamin-d-covid.shotwell.ca/ https://vitamin-d-covid.shotwell.ca/ https://bjsm.bmj.com/content/early/2021/07/21/bjsports-2021-104203 https://bjsm.bmj.com/content/early/2021/07/21/bjsports-2021-...

mrfusion 5y ago

If a study found the opposite, would we be hearing about it?

belorn 5y ago

Its interesting that the article do not mention a rather interesting finding in the study. For the age groups of < 50 years the effect was not statistically significant with the control and the mask wearing villages having similar rate of covid-19. Why aren't masks effective to reduce the spread for that age group? The discussion part of the study don't explore it. Is the distancing behavior of people aged 50 or higher different than those below? I would like to see further studies being done on the younger demographic in order to explain why the data is looking like it is.

jasonlaramburu 5y ago
Maybe lower mask adherence among younger people or different behaviors-- older people in villages might stay at home more.
- packetlost 5y ago
  if the latter is true, then wouldn't that be an indicator that masks do not, in fact, work as well as thought?
  - jasonlaramburu 5y ago
    It could, or it could mean that the protective effect of surgical masks is most pronounced indoors.
jacquesm 5y ago
Compliance.
hncurious 5y ago
They did report that physical distancing increased in villages that were given masks, so that may explain it. Unfortunately they didn't untangle that effect? How do we know to what degree it was the masks vs increased distancing?
mywittyname 5y ago
> Why aren't masks effective to reduce the spread for that age group? This is a good question and I think it is an important one since the title implies a different situation than what was actually tested. So the 11% reduction was due to an effort to increase mask wearing compliance by means of... > Providing free masks, informing people about the importance of covering both the mouth and nose, reminding people in-person when they were unmasked in public, and role-modeling by community leaders It's probably not that masks are less effective on people under 50, but that the information campaign was less effective at influencing that group to wear their masks. Also, the results are interesting: > The observers found that just over 13% of people in the villages that received no interventions wore a mask properly, compared with more than 42% of people in the villages where each household received free masks and in-person reminders to wear them. It seems that there is much more progress that can be made in getting people to wear masks. And we still don't know how effective 95%+ compliance will be at reducing the spread. Finally, the report does note that villages provided with cloth masks had worse outcomes than those who were provided with surgical masks.

alecst 5y ago

My first reaction was to consider this as pretty damning of mass use. But when I considered it more I don't think the study is as damning of masks as it is of mask mandates. The problem is only ~30% more people wore masks in the intervention arm of the study. So the best possible outcome, removing 30% from the infection group entirely (essentially taking them out of the population -- a "perfect spherical mask" approximation), is a 30% reduction in cases. Which is substantial, but no one expects masks to be that effective anyway. 11% seems a reasonable ballpark. If everyone had worn masks it would have been easier to measure the effect of just the masks. Still, it's worth considering the big picture. If mask mandates aren't enforced, they're not worth a whole lot. Especially if you have limited political capital to spend.

pseudalopex 5y ago
The interventions the article mentioned did not include a mandate.
- alecst 5y ago
  Yea true, more like encouraging people to wear masks.

nikolay 5y ago

Reduce but not by much. One could buy KN95 masks at comparable costs and wear them longer and be safer. Not sure why people would get a surgical mask. Governments must subsidize quality masks!

fulafel 5y ago

Is to possible to measure or control for behavioral, vs direct transmission blocking, effects of masks? If they seem more effective for old people, could it be that they help remind people about the ongoing pandemic and infection risk, and signal that mask wearers prefer to keep distance to others.

incrudible 5y ago

TLDR; ARR/month estimate: Lower bound: 2.86E-05 Mid-range: 8.91E-05 Upper-Bound: 1.50E-04 That's on page 90.

BobJackienine 5y ago

It wasn't the mask wearing it was the distancing when I was in the military mission oriented personal protection taught us never to issue surgical masks when they're touched they're contaminated and need to be thrown out. ITT: either this place is turned into Reddit with a bunch of retards bots or none of you can read statistics or can even do basic math.