The American Journal of Medicine published a study that looked at 77 studies used by the Morbidity and Mortality Weekly Report (MMWR) concerning masks. MMWR heavily influenced mask policies in the United States. This study found MMWR drew conclusions about mask wearing using unsupported data.
MMWR publications pertaining to masks drew positive conclusions about mask effectiveness >75% of the time despite only 30% testing masks and <15% having statistically significant results. No studies were randomized, yet over half drew causal conclusions. The level of evidence generated was low and the conclusions were most often unsupported by the data. Our findings raise concern about the reliability of the journal for informing health policy.
An analysis of studies pertaining to masks in Morbidity and Mortality Weekly Report: Characteristics and quality of studies from 1978 to 2023