1. Stanford Prevention Research Center, School of Medicine, Stanford University, Hoover Pavilion, MC 5705, 211 Quarry Road, Room N229, Stanford, CA 94305-5705, United States
2. Department of Physiological Nursing, School of Nursing, University of California, San Francisco, United States
3. Department of Epidemiology and Biostatistics, School of Medicine, University of California, San Francisco, United States