1Stanford Prevention Research Center, Department of Medicine, Stanford University, Stanford, California.
2Stanford Prevention Research Center, Department of Medicine, Stanford University, Stanford, California; Center for Tobacco Control Research and Education, University of California, San Francisco, California.
3Stanford Prevention Research Center, Department of Medicine, Stanford University, Stanford, California; Product Development Regulatory, Genentech, South San Francisco, California.
4Stanford Prevention Research Center, Department of Medicine, Stanford University, Stanford, California; Department of Psychology, University of California, Berkeley, California.
5HealthTap, Palo Alto, California.
6Stanford Prevention Research Center, Department of Medicine, Stanford University, Stanford, California. Electronic address: jpro@stanford.edu.