U.S. federal research funding triggers regulations to protect human subjects known as the Common Rule, a collaborative government effort that spans seventeen federal agencies. The Department of Health and Human Services has been in the process of comprehensively reevaluating the Common Rule, which designates specific groups as "vulnerable populations"--pregnant women, fetuses, children, prisoners, and those with serious cognitive challenges--and imposes heightened protections of them. Given the vulnerabilities of those who confront end-of-life decisionmaking, should the regulatory standard be...