[1] Univ Calif Davis, Dept Publ Hlth Sci, Div Biostat, One Shields Ave,Med Sci 1C, Davis, CA 95616 USA
[2] Univ Louisville, Dept Neurosurg, Louisville, KY 40292 USA
[3] Univ Calif Davis, Med Ctr, Dept Surg, Sacramento, CA 95817 USA
[4] Univ Calif Davis, Med Ctr, Dept Emergency Med, Sacramento, CA 95817 USA
[5] Univ Calif Davis, Med Ctr, Dept Pediat, Sacramento, CA 95817 USA
[6] Seattle Sci Fdn, Seattle, WA USA