[1] VA Palo Alto Healthcare Syst, Dept Med, Palo Alto, CA 94304 USA
[2] Univ Calif San Francisco, Dept Med, Div Hosp Med, San Francisco, CA USA
[3] Harvard Univ, Sch Med, Brigham & Womens Hosp, BWH Acad Hospitalist Serv, Boston, MA USA
[4] Harvard Univ, Sch Med, Brigham & Womens Hosp, Div Gen Med, Boston, MA USA
[5] Harvard Univ, Sch Publ Hlth, Dept Biostat, Boston, MA 02115 USA