[1] Univ Calif San Francisco, Philip R Lee Inst Hlth Policy Studies, San Francisco, CA 94143 USA
[2] Univ Calif San Francisco, Dept Surg, San Francisco, CA USA
[3] Univ Calif San Francisco, Dept Epidemiol & Biostat, San Francisco, CA 94143 USA
[4] Univ Calif San Francisco, Dept Surg, Sect Colorectal Surg, San Francisco, CA USA