[1] Univ Calif Davis, Dept Family & Community Med, Sch Med, Sacramento, CA 95817 USA
[2] Oregon Hlth & Sci Univ, Dept Med Informat & Clin Epidemiol, Oregon Evidence Based Practice Ctr, Portland, OR 97201 USA
[3] Univ Calif Davis, Ctr Healthcare Policy & Res, Sch Med, Sacramento, CA 95817 USA
[4] Kaiser Permanente, Dept Med, Folsom, CA USA
[5] Univ Calif San Francisco, Sch Med, Dept Obstet Gynecol & Reprod Sci, San Francisco, CA 94143 USA
[6] Univ Calif San Francisco, Sch Med, Dept Epidemiol & Biostat, San Francisco, CA 94143 USA