[1] Univ Massachusetts, Dept Med, Sch Med, Worcester, MA 01655 USA
[2] Univ Massachusetts, Div Epidemiol, Dept Quantitat Hlth Sci, Sch Med, Worcester, MA 01655 USA
[3] Univ Massachusetts, Ctr Outcomes Res, Sch Med, Worcester, MA 01655 USA
[4] Univ Massachusetts, Dept Emergency Med, Sch Med, Worcester, MA 01655 USA