[1] Boston Univ, Sch Med, Clin Epidemiol Res & Training Unit, Boston, MA 02118 USA
[2] Boston Univ, Slone Epidemiol Ctr, Boston, MA 02215 USA
[3] Univ Penn, Sch Med, Dept Biostat & Epidemiol, Ctr Clin Epidemiol & Biostat, Philadelphia, PA 19104 USA
[4] Univ Penn, Sch Med, Ctr Educ & Res Therapeut, Philadelphia, PA 19104 USA
[5] Univ Penn, Sch Med, Div Gen Internal Med, Dept Med, Philadelphia, PA 19104 USA