[1] Dartmouth Med Sch, Ctr Evaluat Clin Sci, Dept Community & Family Med, Hanover, NH 03755 USA
[2] Dartmouth Med Sch, Dept Pediat, Hanover, NH 03755 USA
[3] Univ Washington, Dept Pediat, Seattle, WA 98195 USA
[4] Grp Hlth Cooperat Puget Sound, Ctr Hlth Studies, Seattle, WA 98101 USA