[1] Harvard Med Sch, Boston, MA 02115 USA
[2] Harvard Pilgrim Inst, Dept Populat Med, Drug Policy Res Grp, Boston, MA USA
[3] Harvard Med Sch, Dept Populat Med, Boston, MA USA
[4] Harvard Pilgrim Hlth Care Inst, Boston, MA USA
[5] Ontario Inst Canc Res, Toronto, ON, Canada