Around the world and within the U.S., the percentage of people wearing masks during the Covid-19 pandemic has varied enormously. What explains this? A new study co-authored by an MIT faculty member finds that a public sense of “collectivism” clearly predicts mask usage, adding a cultural and psychological perspective to the issue. The study uses a series of datasets about mask usage and public attitudes, along with well-established empirical indices of collectivism, to evaluate the impact of those cultural differences on this element of the pandemic response. “Our data both…