[1] Univ Penn, Perelman Sch Med, Ctr Clin Epidemiol & Biostat, Dept Biostat & Epidemiol, Philadelphia, PA 19104 USA
[2] Univ Penn, Perelman Sch Med, Dept Otorhinolaryngol Head & Neck Surg, Philadelphia, PA 19104 USA
[3] Univ Arizona, Dept Surg, Tucson, AZ USA
[4] Philadelphia Vet Affairs Med Ctr, Philadelphia, PA USA