[1] Univ Penn, Dept Biostat & Epidemiol, Sch Med, Ctr Clin Epidemiol & Biostat, Philadelphia, PA 19104 USA
[2] Abramson Canc Ctr, Philadelphia, PA USA
[3] Univ Minnesota, Sch Med, Dept Dermatol, Minneapolis, MN 55455 USA
[4] Mayo Clin, Dept Phys Med & Rehabil, Rochester, MN USA