[1] Childrens Hosp, Div Adolescent Young Adult Med, Dept Med, Boston, MA 02215 USA
[2] Harvard Univ, Sch Med, Boston, MA USA
[3] Smith Coll, Dept Math & Stat, Northampton, MA 01063 USA
[4] Univ Guelph, Dept Family Relat & Appl Nutr, Guelph, ON N1G 2W1, Canada
[5] Brigham & Womens Hosp, Dept Med, Channing Lab, Boston, MA USA
[6] Harvard Univ, Sch Publ Hlth, Dept Soc Human Dev & Hlth, Boston, MA 02115 USA
[7] Harvard Univ, Sch Publ Hlth, Dept Epidemiol, Boston, MA 02115 USA