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Letters Danish mask study

Danish mask study: masks, media, fact checkers, and the interpretation of scientific evidence

BMJ 2020; 371 doi: (Published 23 December 2020) Cite this as: BMJ 2020;371:m4919
  1. Simon Thornley, senior lecturer1,
  2. Michael D Jackson, research fellow2,
  3. Gerhard Sundborn, senior lecturer3
  1. 1Section of Epidemiology and Biostatistics, University of Auckland, Building 507, 22-30 Park Road, Grafton, Auckland 1142, New Zealand
  2. 2School of Biological Sciences, University of Canterbury, Christchurch, New Zealand
  3. 3Section of Pacific Health, University of Auckland, Auckland, New Zealand
  1. s.thornley{at}

The results of the Danmask-191 trial1—which, by conventional interpretation, showed that wearing masks had no effect on the prevention of covid-19 spread—are contested. An editorial for The BMJ disagreed with convention and criticised the labelling of the “no effect” reading by Oxford professors Heneghan and Jefferson as “false information.”2 We were also labelled “misleading” after our “no effect” interpretation. …

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