[1] Brigham & Womens Hosp, Div Pharmacoepidemiol & Pharmacoecon, Boston, MA 02120 USA
[2] Childrens Hosp Philadelphia, Philadelphia, PA 19104 USA
[3] Univ Penn, Philadelphia, PA 19104 USA
[4] Pusan Natl Univ, Pusan 609735, South Korea
[5] Univ British Columbia, Vancouver, BC V5Z 1M9, Canada
[6] Dartmouth Hitchcock Med Ctr, Lebanon, NH 03766 USA