Scott Alexander reviews evidence on face mask effectiveness against coronavirus, concluding they likely offer some protection despite CDC recommendations against general public use. Longer summary

This post examines the effectiveness of face masks in preventing coronavirus transmission. It reviews theoretical reasons, case-control studies, randomized trials, and laboratory studies on surgical masks and N95 respirators. The author concludes that while not perfect, surgical masks likely offer some protection against infection in high-risk situations. The post also discusses the CDC's recommendations against mask use for the general public, suggesting this may be due to high standards of proof in medical communication rather than intentional deception. The author ultimately recommends considering mask use in high-risk situations if supplies are not limited, while emphasizing that masks are not a substitute for avoiding such situations when possible. Shorter summary

Scott Alexander examines evidence on marijuana legalization's effects on usage, health, and drug war costs, finding uncertainties too large for firm conclusions but suggesting traffic accidents may be the key factor. Longer summary

Scott Alexander examines the evidence around marijuana legalization, looking at its effects on usage rates, health impacts, and costs of the drug war. He finds that decriminalization and medical marijuana don't seem to increase youth usage much, but full legalization might increase adult use by 25-50%. Health effects are unclear but may include IQ declines and slightly increased psychosis risk. The costs of the drug war are significant in terms of arrests and spending, but relatively few people are in prison solely for marijuana. Scott attempts a utilitarian analysis comparing costs and benefits of legalization, but finds the uncertainties too large to draw firm conclusions. He suggests the most important factor may be how legalization affects traffic accidents. Shorter summary