The authors of a study based on an enormous randomized research project in Bangladesh say their results offer the best evidence yet that widespread wearing of surgical masks can limit the spread of the coronavirus in communities. The preprint paper, which tracked more than 340,000 adults across 600 villages in rural Bangladesh, is by far the largest randomized study on the effectiveness of masks at limiting the spread of coronavirus infections. The study's authors — led by principal investigators Jason Abaluck, Laura Kwong, an assistant professor of environmental health sciences at Berkeley's School of Public Health, Steve Luby, Ahmed Mushfiq Mobarak and Ashley Styczynski — are a globe-spanning team that includes researchers from Yale, Stanford and the Bangladeshi nonprofit GreenVoice.