A recent study of mask effectiveness is hailed by two Oxford professors of evidence-based medicine in the following terms:
Yesterday marked the publication of a long-delayed trial in Denmark which hopes to answer that very question. The ‘Danmask-19 trial’ was conducted in the spring with over 3,000 participants, when the public were not being told to wear masks but other public health measures were in place. Unlike other studies looking at masks, the Danmask study was a randomised controlled trial – making it the highest quality scientific evidence.Heneghan & Jefferson, “Landmark Danish study shows face masks have no significant effect,” The Spectator, 19 Nov 2020.
After summarizing the research of the article (linked above), they summarize its conclusion:
And now that we have properly rigorous scientific research we can rely on, the evidence shows that wearing masks in the community does not significantly reduce the rates of infection.Ibid., emphasis mine.
However, this is the conclusion of the actual scientific paper:
The recommendation to wear surgical masks to supplement other public health measures did not reduce the SARS-CoV-2 infection rate among wearers by more than 50% in a community with modest infection rates, some degree of social distancing, and uncommon general mask use. The data were compatible with lesser degrees of self-protection.Bundgaard, et. al., 2020: https://www.acpjournals.org/doi/10.7326/M20-6817
A few lines previously, the authors explain the qualification of “by more than 50%” as follows:
Although the difference observed was not statistically significant, the 95% CIs are compatible with a 46% reduction to a 23% increase in infection.Ibid.
Now, how one logically revises the above, limited conclusion of the actual article—with all of its qualifiers, including the fact that general mask use was not in place and the reduction recorded within confidence intervals—into “the evidence shows that wearing masks in the community does not significantly reduce the rates of infection” seems possible only by way of a style of vague abstraction that trades on the blurred limits of a limited scientific experiment for the purported good of the reading public.
What is the danger? Coronavirus logic now extrapolates from such a revision, equivocating through loss of precision, and confidently but groundlessly concludes that the wearing of masks is not effective.
Indeed, the actual study—if one reads beyond the abstract—confirms this:
Although no statistically significant difference in SARS-CoV-2 incidence was observed, the 95% CIs are compatible with a possible 46% reduction to 23% increase in infection among mask wearers. These findings do offer evidence about the degree of protection mask wearers can anticipate in a setting where others are not wearing masks and where other public health measures, including social distancing, are in effect. The findings, however, should not be used to conclude that a recommendation for everyone to wear masks in the community would not be effective in reducing SARS-CoV-2 infections, because the trial did not test the role of masks in source control of SARS-CoV-2 infection.Ibid, my emphasis.
The truth, even more so than public health, is a common good. Critique of this critique, on any point where it falls short, is welcome.