[1] Univ Penn, Sch Vet, Dept Clin Studies Philadelphia, 3900 Delancey St, Philadelphia, PA 19104 USA
[2] Univ Penn, Perelman Sch Med, Dept Biostat & Epidemiol, Philadelphia, PA 19104 USA
[3] Univ Penn, Ctr Clin Epidemiol & Biostat, Philadelphia, PA 19104 USA
[4] Univ Penn, Ctr Interact Anim & Soc, Sch Vet Med, Philadelphia, PA 19104 USA