Case for Mask Mandate Rests on Bad Data

A top scientific journal lowballs the percentage of Americans who are already covering their faces

By Phillip W. Magness. Excerpts:

"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."

"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."

"The IHME team didn’t adjust. Its Sept. 21 estimates of U.S. mask adoption tracked the YouGov survey results beginning in March, but the two began to diverge in April. From mid-June on, the IHME’s Sept. 21 model understated mask usage by about 30 percentage points.

The YouGov survey isn’t alone, and the IHME’s substantially lower estimates make it a clear data outlier. A separate survey by Carnegie Mellon University shows that mask usage exceeded 80% in 41 of the 50 U.S. states as of Sept. 21. Today that’s up to 44 states. In California and the hard-hit Northeast, mask adoption exceeded 90%. These results align with a report from the Centers for Disease Control and Prevention, released a few days after the IHME paper, which shows U.S. mask adoption hitting 88.7% in June.

Part of the problem is that the IHME’s 49% mask-use estimate includes only those survey respondents who say they always wear a mask in public. This narrow definition excludes a great many people who regularly wear masks. YouGov, which gives respondents the option of saying they almost always wear masks, finds a mask-usage rate of 80% in its latest survey of Americans, with only 6% shunning the practice altogether."

"The journal has told the Retraction Watch website that its model now assumes 68% U.S. mask usage—still likely too low—along with a substantially smaller projection of lives saved than the one it published."