[1] Univ Calif San Francisco, Dept Med, San Francisco, CA 94143 USA
[2] Duke Univ, Med Ctr, Dept Biostat & Bioinformat, Durham, NC USA
[3] Duke Univ, Med Ctr, CALGB Stat Ctr, Durham, NC USA
[4] Wake Forest Univ, Dept Med, Winston Salem, NC 27109 USA
[5] Univ Chicago, Dept Med, Chicago, IL 60637 USA