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• An article quotes two sentences from a CDC study out of context to claim that mask mandates had a statistically insignificant effect on coronavirus case and death rates.
• The study actually found the opposite. Mask mandates were associated with statistically significant decreases in county-level daily COVID-19 case and death growth rates.
A new study from the Centers for Disease Control and Prevention found that widespread mask use significantly helped stem the spread of the coronavirus.
Yet a conservative news site claims that the study actually found the opposite, quoting two sentences out of context to make it appear that mask mandates had an insignificant effect on coronavirus case rates.
"CDC: Mask Mandates Made No Statistical Difference," reads the headline of an article published in Texas Scorecard that is being shared widely on Facebook.
The article was flagged as part of Facebook’s efforts to combat false news and misinformation on its News Feed. (Read more about our partnership with Facebook.)
We interviewed three public health experts familiar with the study and a spokesperson from the CDC. They were unanimous: The article’s reading of the study is off-base.
"It’s not accurate at all to say that mask mandates played no role in decreasing COVID-19 case rates and deaths," said Cindy Prins, a clinical associate professor of epidemiology at the University of Florida College of Public Health and Health Professions. "People are completely misunderstanding the study design if they are coming to that conclusion."
Both the study and the article were released as state governments considered lifting mask requirements, with five states — Texas, North Dakota, Mississippi, Iowa and Montana — opting to do so.
We reached out to the author of the article but did not hear back.
The main takeaway from the study was that "mask mandates were associated with statistically significant decreases in county-level daily COVID-19 case and death growth rates," said CDC spokesperson Jason McDonald.
This conclusion is stated multiple times in the agency’s study.
As evidence for its claims, the Texas Scorecard article quotes two sentences from the study out of context.
"Daily case and death growth rates before implementation of mask mandates were not statistically different from the reference period," reads the first.
The article takes the term "reference period" to refer to the period after the mask mandate was implemented. However, the report explicitly defines the "reference period" as the 20 days before the mask mandates started.
"When the authors (of the CDC study) say ‘daily case and death growth rates before implementation of mask mandates were not statistically different from the reference period,’ they mean that rates 60-21 days before mandates were not statistically different from those 20-1 days before the mandate," explained Johns Hopkins epidemiologist Nikolas Wada.
The CDC study compared case rates from these two time periods to make sure that there wasn’t already a downward trend in coronavirus case and death rates before the mask mandate was implemented. According to McDonald, this helped the CDC to rule out other factors that could have accounted for the decrease.
The Texas Scorecard article also quotes the following sentence from the CDC study out of context: "Changes in daily COVID-19 case and death growth rates were not statistically significant 1-20 and 21-40 days after restrictions were lifted."
The sentence appears at a point in the study that discusses the effect of indoor dining on coronavirus case and death rates. Although the study found that allowing restaurants to serve customers initially had a statistically insignificant effect on coronavirus case rates, the effect did gradually become statistically significant sometime between the 41st and 60th day after dining restrictions were lifted.
Texas Scorecard wrote that a CDC study found that "Mask Mandates Made No Statistical Difference" on coronavirus case rates.
That’s wrong and amounts to a ridiculous reading of a study that actually found the opposite: Mask mandates were associated with statistically significant decreases in county-level daily COVID-19 case and death growth rates.
Pants on Fire!
CDC, Association of State-Issued Mask Mandates and Allowing On-Premises Restaurant Dining with County-Level COVID-19 Case and Death Growth Rates — United States, March 1–December 31, 2020, Mar. 12, 2021
Centers for Disease Control and Prevention, Trends in County-Level COVID-19 Incidence in Counties With and Without a Mask Mandate — Kansas, June 1–August 23, 2020, Nov. 27, 2020
Texas Scorecard, CDC: Mask mandates made no statistical difference, Mar. 13, 2021
Science of the Total Environment, Understanding transmission and intervention for the COVID-19 pandemic in the United States, 2020
Email interview with Jason McDonald, CDC spokesperson, Mar. 19, 2021
Email interview with Cindy Prins, a clinical associate professor of epidemiology at the University of Florida College of Public Health and Health Professions, Mar. 18, 2021
Email interview with Mary Kathryn Grabowski, an assistant professor in epidemiology at Johns Hopkins University, Mar. 18, 2021
Email interview with Nikolas Wada, an epidemiologist at Johns Hopkins University, Mar. 19, 2021
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