The top scientific journal Nature Medicine published a study on Oct. 23 with an astounding claim: By simply wearing masks at higher rates, Americans could prevent as many as 130,000 Covid-19 fatalities by the end of February 2021. Produced by the University of Washington’s Institute for Health Metrics Evaluation, or IHME, the study garnered immediate acclaim.
More than 100 news outlets trumpeted the study’s findings in the days following its publication—“The Price for Not Wearing Masks: Perhaps 130,000 Lives” was the New York Times ’s headline—and a few hundred more articles have been written since. Reporting was often paired with calls for a national mask mandate, echoing President-elect Biden and now Anthony Fauci, the top U.S. infectious-disease official. The study was also invoked by Francis Collins, head of the National Institutes of Health, to push for stricter masking requirements. Recognizing the potential importance, Nature Medicine rushed the study into print after an expedited peer-review process that took only seven days to complete.
Unfortunately, the IHME modelers’ findings contained an error that even minimal scrutiny should have caught. The projected number of lives saved, and the implied case for a mask mandate, are based on a faulty statistic. Using a months-old survey, IHME modelers assumed erroneously that the U.S. mask-adoption rate stood at only 49% as of late September, and therefore had plenty of room to increase to “universal adoption,” defined as 95%, or to a more plausible 85%. According to more recent survey findings, however, America’s mask-adoption rate has hovered around 80% since the summer.
New numbers would completely alter the IHME study’s findings. If 80% of Americans already wear masks, a new mandate could add only a few percentage points to the mask-adoption rate instead of nearly doubling it. Additional gains would be small and certainly nowhere near 130,000 lives saved.
The study’s documentation suggests the 49% figure came from survey data collected by the data-analytics firm Premise between April 23 and June 26. Although the paper in Nature Medicine explicitly labeled these data as current as of Sept. 21, they weren’t. And other surveys paint a very different picture. The YouGov/Economist tracking poll finds that the U.S. mask-usage rate skyrocketed in late spring and hit 78% on July 14. It has hovered in the high 70s and low 80s ever since.
