[1] Harvard Univ, Sch Med, Dept Ambulatory Care & Prevent, Boston, MA 02215 USA
[2] Harvard Pilgrim Healthcare, Boston, MA USA
[3] Harvard Univ, Sch Med, Dept Pediat, Boston, MA 02115 USA
[4] Brigham & Womens Hosp, Channing Lab, Boston, MA 02115 USA
[5] Grp Hlth Cooperat Puget Sound, Ctr Hlth Studies, Seattle, WA USA
[6] Northwestern Univ, Sch Med, Rush Presbyterian St Lukes Med Ctr, Dept Immunol Microbiol, Chicago, IL USA
[7] Northwestern Univ, Sch Med, Rush Presbyterian St Lukes Med Ctr, Dept Pediat, Chicago, IL USA
[8] Northwestern Univ, Sch Med, Rush Prudential Hlth Plan, Chicago, IL USA
[9] Northwestern Univ, Sch Med, Ctr Healthcare Studies, Chicago, IL USA
[10] Northwestern Univ, Sch Med, Dept Med, Div Gen Med, Chicago, IL USA
[11] Edward Hines Jr VA Hosp, Midwest Ctr Hlth Serv & Policy Res, Hines, IL 60141 USA