15/n In this case, the study found that 1.8% of people in the mask group had antibodies, compared to 2.1% of people in the non-mask group But those are just the RAW figurespic.twitter.com/NtiZuV9Uml
Epidemiologist. Writer (Guardian, Observer etc). "Well known research trouble-maker". PhDing at @UoW Host of @senscipod Email gidmk.healthnerd@gmail.com he/him
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15/n In this case, the study found that 1.8% of people in the mask group had antibodies, compared to 2.1% of people in the non-mask group But those are just the RAW figurespic.twitter.com/NtiZuV9Uml
16/n If we use the Rogen-Gladen estimator, which is a pretty standard correction for test characteristics, we see instead that 1.59% and 1.95% of people in masks/no masks were probably infected, respectivelypic.twitter.com/d4rPZ5kJVw
I may be getting it wrong but would you mind checking your calculations? I get 1.07% and 1.51% respectively using the formula above. I use 90.2% for sensitivity and 99.2% for specificity as provided in the paper. [I get 0.65% and 1.11% for the sensitivity analysis of the authors]
So, I was slightly off in those numbers, it's actually 1.56% vs 2.09% using the main results and the sens/spec from the internal validation study rather than the manufacturer. You have to take into account that some infections were confirmed by PCRpic.twitter.com/5jpxWkUItP
So it's 1.8-0.2 = 1.6% for masks and 2.1-0.4 = 1.7% for non-masks, corrected that becomes 1.34% and 1.46%, add back in the PCR (for whom spec is ~100%) and you get 1.54% and 2.06%
Ugh, just realized it should be 2.1-0.6 for the non-masks, which changes the numbers again to 1.54% vs 1.82%. Same general problem, an estimated 1.68% infected in the study
Sorry to be a pain, but can you check your Rogan-Gladen correction and/or the sensitivity/specificity numbers you use? When I use the formula, I get lower true prevalence. In the fully corrected version of yours, I get to 1.04% (masks) and 1.43% (control).
I'm still not excluding the pre test people tho, this is just the numbers from the main analysis
Me neither in the numbers above. Take mask group. AB confirmed 37 out of 2383 = 1.55%. Rogan-Gladen correction with specificity 99.2% and sensitivity 90.2%: (1.55%+99.2%-1)/(99.2%+90.2%-1) = 0.75%/89.4% = 0.84%
Yep but I'm using the internal validation numbers for sens/spec rather than the manufacturer numbers, so 82.5% and 99.5%
I'm generally very mistrustful of manufacturer numbers because they are almost always higher than those found in validation studies by other people 
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