[1] Univ Pittsburgh, Grad Sch Publ Hlth, Dept Hlth Policy & Management, Pittsburgh, PA 15260 USA
[2] Univ Pittsburgh, Grad Sch Publ Hlth, Dept Biostat, Pittsburgh, PA 15261 USA
[3] Newcastle Univ, Fac Med Sci, Populat Hlth Sci Inst, Newcastle Upon Tyne, Tyne & Wear, England
[4] Univ Pittsburgh, Grad Sch Publ Hlth, Dept Epidemiol, Pittsburgh, PA 15260 USA