September 03, 2021

Much-touted Bangladesh study of masks is a snark

Multiple accounts have popped up (e.g. here) saying that the study vindicates mask-wearing. It does not. Just two quotes from the study abstract tell the tale:

"Neither participants nor field staff were blinded to intervention assignment"

"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"

For a start, the study was of people with "COVID-like symptoms", not actual disease and there was NO data on deaths. So there is a lot of room for slippage there.  How often were the "symptoms" actually indicative of COVID infection? 

Secondly, the figures for mask-wearers and non-mask-wearers differed only slightly (7.62% vs 8.62%) -- to a  degree readily explainable by the fact that the study was not blinded.  The experimenters knew who the wearers and non-wearers were and it is routine that such a circumstance gives results favourable to the hypothesis.

Not blinding the study was a huge breach of scientific protocol and renders the results of zero authority.

https://www.poverty-action.org/sites/default/files/publications/Mask_RCT____Symptomatic_Seropositivity_083121.pdf



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