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Comment by tboyd47 | Hacker News Reader

Thanks. That study doesn't measure any sort of disease spread. It measures the density of candle smoke on either side of the mask.

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Not at all, perhaps you meant another commenter? From the link "Before exhaled breath collection, each participant was randomly allocated in a 1:1 ratio to either wearing a surgical face mask (cat. no. 62356, Kimberly-Clark) or not during the collection. [...] Participants were then invited to provide a second exhaled breath sample of the alternate type (for example if the participant was first assigned to wearing a mask they would then provide a second sample without a mask)"

They actually tested infected patients with and without mask.

>We detected coronavirus in respiratory droplets and aerosols in 3 of 10 (30%) and 4 of 10 (40%) of the samples collected without face masks, respectively, but did not detect any virus in respiratory droplets or aerosols collected from participants wearing face masks, this difference was significant in aerosols and showed a trend toward reduced detection in respiratory droplets (Table 1b).

This study is incredibly small, and operating on the limits of significance. Its hardly conclusive, and was done under fairly extreme conditions (30 mins in close proximity) compared to the scenarios in which masks are mandated today. The authors even mention that, for those who did not cough, no detectable virus was identified regardless of whether a mask was worn. Considering that the point of mandatory masking is to prevent asymptomatic transmission from brief interactions with strangers, I just don't find this study very convincing as a scientific basis for a mask mandate.

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