Facing unprecedented uncertainty and drastic trade-offs between public health and other forms of human well-being, policymakers during the Covid-19 pandemic have sought the guidance of epidemiologists and economists. Unfortunately, while both groups of scientists use many of the same basic...

The effect of face masks on Covid-19 transmission is crucial for the health of populations. The effectiveness of face masks in reducing the transmission of Covid-19 varies across primary evidence. To perform a quantitative meta-analysis, we collected 258 estimates from 44 primary studies...