Randomized experiments commonly compare subjects receiving a treatment to subjects receiving a placebo. An alternative design, frequently used in field experimentation, compares subjects assigned to an untreated baseline group to subjects assigned to a treatment group, adjusting statistically...

We recommend the immediate universal adoption of cloth facemasks, including homemade, and accompanying policies to increase the supply of medical masks for health workers. Universal adoption will likely slow the spread of the COVID-19 virus by reducing transmission from asymptomatic individuals....