[1] Univ Calif Davis, Dept Dermatol, 3301 C St,Suite 1400, Sacramento, CA 95816 USA
[2] Univ Toronto, Family & Community Med, Toronto, ON M5S 1A1, Canada
[3] Santa Clara Valley Med Ctr, Dept Med, San Jose, CA 95128 USA
[4] Stanford Univ, Sch Med, Stanford, CA 94305 USA
[5] Univ Calif Davis, Dept Stat, Sacramento, CA 95817 USA
[6] Univ Calif Davis, Dept Publ Hlth, Div Biostat, Sacramento, CA 95817 USA