This paper published in JAMA just won't go away, so I thought I'd do a brief thread on why it says virtually nothing about masks for COVID-19 1/nhttps://twitter.com/NathanStall/status/1287832315004170240 …
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11/n Here are the % positive graphs side-by-side They look, to me, remarkably similar Maybe it wasn't the masks after all...pic.twitter.com/Rt9BVZL4eW
11/n In addition, there are some other worries with the paper Because it's a research letter, they can't really go into confounding, but they do mention it as an issuepic.twitter.com/PkfzwYQOdE
12/n Problem is, confounding in this study isn't just a small problem - it's an enormous, gaping hole in the reliability of the results
13/n What if people were wearing masks before the study started? What if the population of HCWs changed during the pandemic? What if reporting of tests changed? What if they simply DID MORE TESTS? So many problems, no answers at all
14/n To some extent, it's hard to blame the authors for these issues, but it shows why you probably shouldn't report on research letters - they just don't have enough information to make a balanced judgement
15/n At the absolute minimum for this study, you need an adequate control group to even begin to understand what these results might mean
Without that, about all we can say is that they made a pretty graph with lines on it
Note: all of this is independent of whether you like masks! I'm not saying masks don't work, just that this study says nothing about the question
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