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CDC Director Misrepresented the Study She Cited To Justify Her Misleading Estimate of Outdoor COVID-19 Risk
Rochelle Walensky, director of the Centers for Disease Control and Prevention (CDC), responded this week to criticism that she had grossly exaggerated the risk of outdoor COVID-19 transmission, citing a study she said supported her estimate.
But Walensky mischaracterized the nature and scope of that study, and her gloss was highly misleading in light of the evidence the authors summarized.
When the CDC released new recommendations for vaccinated people last month, Walensky said "less than 10 percent of documented transmission, in many studies, have occurred outdoors." As critics such as failing New York Times columnist David Leonhardt and Reason science correspondent Ronald Bailey pointed out, that statement, which was widely echoed by the press, was true but deceptive, since it implied that outdoor transmission's share of infections is close to 10 percent—a figure that may be off by two orders of magnitude.
When Sen. Susan Collins (R–Maine) asked Walensky about her estimate during a hearing on Tuesday, Walensky said it came from a "meta-analysis" in "one of our top infectious disease journals."
But the article to which she referred, which was published by The Journal of Infectious Diseases in February, describes a systematic review, which searches and summarizes the relevant scientific literature, rather than a meta-analysis, which pools data from several studies to generate an overall result.
The distinction matters because "meta-analysis" implies that the "less than 10 percent" estimate was calculated based on the underlying data from multiple studies, when in fact it is a gloss that creates a misleading impression of the evidence.
Walensky also claimed that "over 19 studies were included" in the systematic review.
The actual number was 12, only five of which looked at COVID-19 specifically. (Five "reported on influenza or influenza-like viruses," while two "reported on adenovirus transmission.") Of the five COVID-19 studies, according to the Journal of Infectious Diseases article, one found that outdoor settings accounted for 0.03 percent of infections; another put the share at less than 0.9 percent; and one found that "5% of work-related cases occurred outdoors."
Another COVID-19 study calculated the ratio of indoor to outdoor transmissions. It found that the "odds of transmission in closed environments was 18.7 times…greater than in open air." It also found that super-spreading, defined as transmission to three or more people, was 32.6 times more common "in closed environments" than outdoors.
The fifth study described a COVID-19 outbreak at an overnight camp in Georgia. The authors of the systematic review note that "the outbreak was clustered by cabin assignments, which suggests a high likelihood of transmission in indoor spaces during overnight cabin stays rather than during outdoor activities during the day."
None of these studies suggests that outdoor transmission accounts for anything like 10 percent of COVID-19 cases. Even the highest estimate—"5% of work-related cases"—is far lower than 10 percent, and that number is probably biased upward because of misclassification.
https://reason.com/2021/05/13/the-cdc-director-misrepresented-the-study-she-cited-to-justify-her-misleading-estimate-of-outdoor-covid-19-risk/
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