7 ms·

> 77 studies, all published after 2019... 23/77 (29.9%) assessed mask effectiveness, with 11/77 (14.3%) being statistically significant, but 58/77 (75.3%) state

> 77 studies, all published after 2019... 23/77 (29.9%) assessed mask effectiveness, with 11/77 (14.3%) being statistically significant, but 58/77 (75.3%) stated masks were effective. Of these, 41/58 (70.7%) used causal language. Only one mannequin study used causal language appropriately (1.3%). 72/77 (93.5%) pertained to SARS-CoV-2 alone. None cited randomized data. 1/77 (1.3%) cited conflicting evidence. Bit hard to follow here since the talk about "studies that didn't actually study it" seems like a valid critique of study quality but not of mask effectiveness. (But where does the 1978 year in the title come from?) Seems like of 23 studies, 11 of them found statistically significant evidence of improvement; only 1 saw conflicting evidence. Sounds like room for further study and investigation but possibly suggestive of differences in mask quality, correct usage, etc, so deeper dives would certainly be interesting. Obviously in some situations and disciplines nobody questions the value of quality masks, so the "it can't possibly be effective" crowd seems even more unjustified than the "it's effective [even if just 11 out of 23 of the studies said so]" crowd.

kristjansson 2y ago
> study quality And even more specifically, quality of studies (re)published by a single journal, albeit an important one.
kbelder 2y ago
"Are masks effective" is the completely wrong question, anyway. The question should be "how effective are masks?" Preferably, "How effective are masks against X under Y circumstance?" In relation to Covid, I think it's likely masks reduced transmission. But, under normal social environments, did they reduce it by 5% or by 50%? It makes a big policy difference. It seems that studies are coalescing around masks having a 'real but small' effect, but I get it's a hard thing to study.
- marcosdumay 2y ago
  > did they reduce it by 5% or by 50% Either one would cause a dramatic reduction on the (exponential) virus spread. For the actual policy, it shouldn't make a difference. It had feedback mechanisms anyway, because the conditions always change.
  - frognumber 2y ago
    Well, no. It makes a big difference: 1) If the exponent is >1, it doesn't make much difference. Everyone will catch "it," for whatever disease. 2) It makes sense to have interventions prioritized by ROI 3) Many interventions are individual, and there is no exponent. Should I, as a [doctor / immuno-compromised-individual / patient / etc.] wear a mask?
    - marcosdumay 2y ago
      > It makes sense to have interventions prioritized by ROI The thing about masks is that the investment is minimal. Those 5% are still an incredibly large number that makes it a non-brainier. If it decreases another order of magnitude, it may need some analysis. The OP has a point, but it's way beyond the plausibility window.
      - zeroonetwothree 2y ago
        As an individual I would not wear a mask to reduce infection risk by 5%. If it’s more like 90% then that’s something.
        threeseed 2y ago
        But those who are the most likely to be affected i.e. older and vulnerable people would. So in fact whether you wear one or not is far less relevant.
        deleted 2y ago
        [deleted]
        triplesec 2y ago
        You misunderstand the utility of masks, where it is significantly more an infected wearer of the mask who protects others by their wearing. So, being infections before you have symptoms is the problem, which is why people should - as is standard in Japan, for example - wear masks in public whenever they feel unwell or feel a 'cold' coming on.
- postepowanieadm 2y ago
  > I think it's likely masks reduced transmission And your belief is based on what?
  - warcher 2y ago
    Common sense? Restricting exhalation to reduce transmission of airborne disease? Have you never been taught to cover your mouth when you sneeze or cough? Like it would be remarkable if it did nothing. THAT would be a blockbuster result. The thing worth studying is if the effect is worth the trouble or not. It could be worth doing or it could effectively be a waste of time due to whatever other factor.
    - pandaman 2y ago
      Many people have been taught to say "Bless you!" when somebody sneezed too, would it also surprise you that it doesn't affect any airborne virus?
      - amanaplanacanal 2y ago
        Aye, that brings up another issue. What exactly does “airborne” mean? The assumption early on was that Covid was not airborne, and required droplets of a certain size, though I think that changed over time.
        pandaman 2y ago
        We might never know this about COVID as further studying it can only uncover more malfeasance at this point, but traditional airborne stuff like smallpox or measles won't be affected by a dirty bandana on one's mouth or, even, over the nose.
    - neilwilson 2y ago
      Common sense says if you put your hand over your mouth and breath out you will be able to. That says the pressure is overcoming the blockage. The other way round is far more difficult. If you leak then you are wasting your time because in a static air environment you’ll delay the critical level build up by a few minutes at most. Medicine doesn’t like aerosolisation because it sounds too much like miasmia theory. So we have too much focus on droplets and fomites. Fundamentally this should have been sorted with a properly designed trial with the correct protocol of sufficient size to answer the question. Given what was on the line why has it not been done?
- u32480932048 2y ago
  [flagged]
  - supplied_demand 2y ago
    == Instead of getting everyone on the same page, == Your post seems to be continuing this trend. Nobody called anyone “deplorable schmucks” or “puppy kicking grandma killer” but you. Your victimhood really comes out in the language you choose to describe others.
    - throw-the-towel 2y ago
      FWIW I remember this very forum flinging this kind of accusations in 2020.
      - supplied_demand 2y ago
        Even without any examples, I don’t see how revisiting it today gets anyone on the same page. It feels like a way to play the victim.
        ipaddr 2y ago
        [flagged]
        ceejayoz 2y ago
        [flagged]
        pfannkuchen 2y ago
        I have no opinion on this thread but I find it weird when people dig through others’ comment history and try to use it as an argument. If you read the rest of that thread GP states that he was thinking of a specific different police brutality case and mistakenly referred to the George Floyd case instead. I also have no idea what he means by black supremacists there but the ridiculous part of your quote was essentially a typo by GP (allegedly anyway).
- 580515975 2y ago
  https://journals.aps.org/rmp/abstract/10.1103/RevModPhys.95.045001 https://journals.aps.org/rmp/abstract/10.1103/RevModPhys.95.... is one article that provides some insight. It describes the nature of viral particles exhaled in different activities, and explains how effective different masks are at preventing these particles from being inhaled. Separately, I was surprised to see that OP's article looked at studies starting in 1978, since modern electrostatic filtering masks were only patented in 1995--so I'm not sure how meaningful it is to lump studies on older mask technologies in with modern masks.
- chaostheory 2y ago
  Another question most of these studies fail to ask is what is the effectiveness of each type of mask? An N95 mask is going to have a big difference in efficacy vs a surgical mask without a seal. Another issue is that most of these studies are just surveys. Did participants actually use their masks for x hours? Did they use their masks correctly?
jampekka 2y ago
It's probably more addressing the "it can't possibly be ineffective" crowd.
greasegum 2y ago
>But where does the 1978 year in the title come from? This seems to come from the fact that although MMWR has been in publication since 1978, 100% of papers they have published on the topic has been in the past 3.5 years.
efitz 2y ago
Actually the authors interpretation is very different if you read the very next sectio (“Conclusions”): > “Conclusions and Relevance MMWR publications pertaining to masks drew positive conclusions about mask effectiveness over 75% of the time despite only 30% testing masks and <15% having statistically significant results. No studies were randomized, yet over half drew causal conclusions. The level of evidence generated was low and the conclusions drawn were most often unsupported by the data. Our findings raise concern about the reliability of the journal for informing health policy.” I watch Dr Prasad on YouTube and he is pretty interesting IMO. He’s an oncologist but spends a lot of time analyzing medical studies.
- standardUser 2y ago
  With language like that, there's no way to not see this as a hit piece.
  - admissionsguy 2y ago
    Yea, a hit piece on bad science
- majormajor 2y ago
  Yes, I noted that the authors are largely focused on study quality vs actual conclusions about which sorts of masks are what level of effective. And critiquing sloppy science is very necessary. But it's being extended by many to be "masks not useful, full stop" despite largely being about "most studies suck." And the phrasings chosen by the authors make it look like that mis-read/extension is an effect they desire.
ano-ther 2y ago
> But where does the 1978 year in the title come from? Was curious about that too — it’s a slightly unfortunate headline: > Our search, spanning the years 1978 to 2023, identified 83 MMWR published studies on PubMed, all of which were published after 2019.
kukkeliskuu 2y ago
In 2020, I wanted to understand the issue better, so I followed all the links from my government website to any research regarding masks. My government had first stated that wearing masks by the public was not effective and wearing them was actually very selfish and stupid, because masks were needed by the medical professionals. The marrative then took a 180 turn, and then same officials said that masks were effective and not wearing masks was selfish and stupid. They also admitted to lying about the effectiveness of masks before, claiming they wanted save masks for the medical professionals. The only research I could find through links from these government health policy organizations was a meta analysis on the European CDC website, stating that the evidence was inconclusive but masks should be worn anyway. The recommendation of the organization did not follow from their own research. So seeing that the policy had already been based on admitted lies about the research, and that even current research at the time by the organization itself could not support the recommendation, I had to come to a conclusion that mask recommendations were a very political issue. Then I went to read on the methdologies on how the effectiveness can is measured. The general scientific consensus before COVID appreared to be that using masks even by the surgeons did not reduce the risk of tramitting disaease from the surgeon to the patient, but still all surgeons thoughy that it was a good idea to use them. The narrative “at least it prevents droplets from reaching and infecting others” actually relies in the assumption that we know the transmission mechanism for the specific disease. We did not know it at the time for COVID, and I believe we still do not know it conclusively. Some research has been done on the effectiveness of masks on diseases that are transmitted via aerosols. The surprising finding was that although the mask catches the droplets, the mask does not ultimately keep them but the droplets are vaporized in the process, and many of them are turned into aerosols. So using masks actually may increase the transmission for disases that are transmitted through aerosolic particles.
- layla5alive 2y ago
  Respirators are effective down to 300nm - aerosolized viruses are larger than this, around 1uM and larger.
  - amluto 2y ago
    > Respirators are effective down to 300nm Not exactly. For most filter media, ~300nm is the “most penetrating particle size”. The mask is more effective below that.

kristjansson 2y ago

> study quality And even more specifically, quality of studies (re)published by a single journal, albeit an important one.

kbelder 2y ago

"Are masks effective" is the completely wrong question, anyway. The question should be "how effective are masks?" Preferably, "How effective are masks against X under Y circumstance?" In relation to Covid, I think it's likely masks reduced transmission. But, under normal social environments, did they reduce it by 5% or by 50%? It makes a big policy difference. It seems that studies are coalescing around masks having a 'real but small' effect, but I get it's a hard thing to study.

marcosdumay 2y ago
> did they reduce it by 5% or by 50% Either one would cause a dramatic reduction on the (exponential) virus spread. For the actual policy, it shouldn't make a difference. It had feedback mechanisms anyway, because the conditions always change.
- frognumber 2y ago
  Well, no. It makes a big difference: 1) If the exponent is >1, it doesn't make much difference. Everyone will catch "it," for whatever disease. 2) It makes sense to have interventions prioritized by ROI 3) Many interventions are individual, and there is no exponent. Should I, as a [doctor / immuno-compromised-individual / patient / etc.] wear a mask?
  - marcosdumay 2y ago
    > It makes sense to have interventions prioritized by ROI The thing about masks is that the investment is minimal. Those 5% are still an incredibly large number that makes it a non-brainier. If it decreases another order of magnitude, it may need some analysis. The OP has a point, but it's way beyond the plausibility window.
    - zeroonetwothree 2y ago
      As an individual I would not wear a mask to reduce infection risk by 5%. If it’s more like 90% then that’s something.
      - threeseed 2y ago
        But those who are the most likely to be affected i.e. older and vulnerable people would. So in fact whether you wear one or not is far less relevant.
        deleted 2y ago
        [deleted]
        triplesec 2y ago
        You misunderstand the utility of masks, where it is significantly more an infected wearer of the mask who protects others by their wearing. So, being infections before you have symptoms is the problem, which is why people should - as is standard in Japan, for example - wear masks in public whenever they feel unwell or feel a 'cold' coming on.
postepowanieadm 2y ago
> I think it's likely masks reduced transmission And your belief is based on what?
- warcher 2y ago
  Common sense? Restricting exhalation to reduce transmission of airborne disease? Have you never been taught to cover your mouth when you sneeze or cough? Like it would be remarkable if it did nothing. THAT would be a blockbuster result. The thing worth studying is if the effect is worth the trouble or not. It could be worth doing or it could effectively be a waste of time due to whatever other factor.
  - pandaman 2y ago
    Many people have been taught to say "Bless you!" when somebody sneezed too, would it also surprise you that it doesn't affect any airborne virus?
    - amanaplanacanal 2y ago
      Aye, that brings up another issue. What exactly does “airborne” mean? The assumption early on was that Covid was not airborne, and required droplets of a certain size, though I think that changed over time.
      - pandaman 2y ago
        We might never know this about COVID as further studying it can only uncover more malfeasance at this point, but traditional airborne stuff like smallpox or measles won't be affected by a dirty bandana on one's mouth or, even, over the nose.
  - neilwilson 2y ago
    Common sense says if you put your hand over your mouth and breath out you will be able to. That says the pressure is overcoming the blockage. The other way round is far more difficult. If you leak then you are wasting your time because in a static air environment you’ll delay the critical level build up by a few minutes at most. Medicine doesn’t like aerosolisation because it sounds too much like miasmia theory. So we have too much focus on droplets and fomites. Fundamentally this should have been sorted with a properly designed trial with the correct protocol of sufficient size to answer the question. Given what was on the line why has it not been done?
u32480932048 2y ago
[flagged]
- supplied_demand 2y ago
  == Instead of getting everyone on the same page, == Your post seems to be continuing this trend. Nobody called anyone “deplorable schmucks” or “puppy kicking grandma killer” but you. Your victimhood really comes out in the language you choose to describe others.
  - throw-the-towel 2y ago
    FWIW I remember this very forum flinging this kind of accusations in 2020.
    - supplied_demand 2y ago
      Even without any examples, I don’t see how revisiting it today gets anyone on the same page. It feels like a way to play the victim.
      - ipaddr 2y ago
        [flagged]
        ceejayoz 2y ago
        [flagged]
        pfannkuchen 2y ago
        I have no opinion on this thread but I find it weird when people dig through others’ comment history and try to use it as an argument. If you read the rest of that thread GP states that he was thinking of a specific different police brutality case and mistakenly referred to the George Floyd case instead. I also have no idea what he means by black supremacists there but the ridiculous part of your quote was essentially a typo by GP (allegedly anyway).
580515975 2y ago
https://journals.aps.org/rmp/abstract/10.1103/RevModPhys.95.045001 https://journals.aps.org/rmp/abstract/10.1103/RevModPhys.95.... is one article that provides some insight. It describes the nature of viral particles exhaled in different activities, and explains how effective different masks are at preventing these particles from being inhaled. Separately, I was surprised to see that OP's article looked at studies starting in 1978, since modern electrostatic filtering masks were only patented in 1995--so I'm not sure how meaningful it is to lump studies on older mask technologies in with modern masks.
chaostheory 2y ago
Another question most of these studies fail to ask is what is the effectiveness of each type of mask? An N95 mask is going to have a big difference in efficacy vs a surgical mask without a seal. Another issue is that most of these studies are just surveys. Did participants actually use their masks for x hours? Did they use their masks correctly?

jampekka 2y ago

It's probably more addressing the "it can't possibly be ineffective" crowd.

greasegum 2y ago

>But where does the 1978 year in the title come from? This seems to come from the fact that although MMWR has been in publication since 1978, 100% of papers they have published on the topic has been in the past 3.5 years.

efitz 2y ago

Actually the authors interpretation is very different if you read the very next sectio (“Conclusions”): > “Conclusions and Relevance MMWR publications pertaining to masks drew positive conclusions about mask effectiveness over 75% of the time despite only 30% testing masks and <15% having statistically significant results. No studies were randomized, yet over half drew causal conclusions. The level of evidence generated was low and the conclusions drawn were most often unsupported by the data. Our findings raise concern about the reliability of the journal for informing health policy.” I watch Dr Prasad on YouTube and he is pretty interesting IMO. He’s an oncologist but spends a lot of time analyzing medical studies.

standardUser 2y ago
With language like that, there's no way to not see this as a hit piece.
- admissionsguy 2y ago
  Yea, a hit piece on bad science
majormajor 2y ago
Yes, I noted that the authors are largely focused on study quality vs actual conclusions about which sorts of masks are what level of effective. And critiquing sloppy science is very necessary. But it's being extended by many to be "masks not useful, full stop" despite largely being about "most studies suck." And the phrasings chosen by the authors make it look like that mis-read/extension is an effect they desire.

ano-ther 2y ago

> But where does the 1978 year in the title come from? Was curious about that too — it’s a slightly unfortunate headline: > Our search, spanning the years 1978 to 2023, identified 83 MMWR published studies on PubMed, all of which were published after 2019.

kukkeliskuu 2y ago

In 2020, I wanted to understand the issue better, so I followed all the links from my government website to any research regarding masks. My government had first stated that wearing masks by the public was not effective and wearing them was actually very selfish and stupid, because masks were needed by the medical professionals. The marrative then took a 180 turn, and then same officials said that masks were effective and not wearing masks was selfish and stupid. They also admitted to lying about the effectiveness of masks before, claiming they wanted save masks for the medical professionals. The only research I could find through links from these government health policy organizations was a meta analysis on the European CDC website, stating that the evidence was inconclusive but masks should be worn anyway. The recommendation of the organization did not follow from their own research. So seeing that the policy had already been based on admitted lies about the research, and that even current research at the time by the organization itself could not support the recommendation, I had to come to a conclusion that mask recommendations were a very political issue. Then I went to read on the methdologies on how the effectiveness can is measured. The general scientific consensus before COVID appreared to be that using masks even by the surgeons did not reduce the risk of tramitting disaease from the surgeon to the patient, but still all surgeons thoughy that it was a good idea to use them. The narrative “at least it prevents droplets from reaching and infecting others” actually relies in the assumption that we know the transmission mechanism for the specific disease. We did not know it at the time for COVID, and I believe we still do not know it conclusively. Some research has been done on the effectiveness of masks on diseases that are transmitted via aerosols. The surprising finding was that although the mask catches the droplets, the mask does not ultimately keep them but the droplets are vaporized in the process, and many of them are turned into aerosols. So using masks actually may increase the transmission for disases that are transmitted through aerosolic particles.

layla5alive 2y ago
Respirators are effective down to 300nm - aerosolized viruses are larger than this, around 1uM and larger.
- amluto 2y ago
  > Respirators are effective down to 300nm Not exactly. For most filter media, ~300nm is the “most penetrating particle size”. The mask is more effective below that.