A go-to source for health policymakers published studies supporting masking despite their questionable designs and lack of statistical evidence.
One of the most influential federal health journals in the United States has published unsupported claims about the benefits of masks in preventing transmission of COVID-19, according to authors of a manuscript recently accepted for publication in The American Journal of Medicine.
The claims come from the U.S. Centers for Disease Control and Prevention’s (CDC) Morbidity and Mortality Weekly Report (MMWR), which has a powerfully persuasive effect on public health decision-making. How the studies published in the MMWR advance scientific understanding “remain largely opaque to the general public,” the authors wrote in the pre-proofed paper. For this reason, the authors expressed, it is essential to dig into how agency conclusions—and subsequent recommendations that affect citizens across the globe—are made.
Researchers at the University of California–San Francisco and the University of Southern Denmark analyzed 77 studies published after 2019. Conclusions favoring masks were seen in over 75 percent of the studies.
However, after further scrutiny, researchers discovered questionable qualities in most of the studies—qualities that could easily misrepresent results and confuse readers such as health care professionals, researchers, and the public. These qualities included poor study design, scarcity of statistical significance, dubious methods for assessing mask effectiveness, failure to cite conflicting data, and lack of randomization.
Moreover, over 50 percent of the studies failed to use appropriate language when synthesizing findings, labeling results as causal instead of correlative or associative. Scientific principles dictate that causation cannot be inferred based on retrospective, cross-sectional, or observational designs—the only three designs used across all 77 studies.
The findings raise concern about the scientific journal’s reliability for informing health policy—a journal that does not require external peer review before publication, according to the authors.
“Over 60% of the included studies concluded masks were effective without statistically significant evidence to support this,” the authors wrote, noting that less than 15 percent of the 77 studies did provide such evidence. “For clinicians, simply reading the report conclusions pertaining to masks in MMWR may be misleading for advising patients and making health policy recommendations.”
By Mary Gillis
