[1] Univ Pittsburgh, Dept Med, Sch Med,Ctr Res Hlth Care, Dept Hlth Policy & Management,Grad Sch Publ Hlth, Pittsburgh, PA 15213 USA
[2] Drexel Univ, Sch Publ Hlth, Dept Epidemiol & Biostat, Philadelphia, PA USA
[3] Univ Pittsburgh, Grad Sch Publ Hlth, Dept Biostat, Pittsburgh, PA 15261 USA
[4] Univ Pittsburgh, Grad Sch Publ Hlth, Dept Med, Sch Med,Dept Biostat,Ctr Res Hlth Care, Pittsburgh, PA USA