[1] Univ Auckland, Dept Community Hlth, Injury Prevent Res Ctr, Auckland 1, New Zealand
[2] Univ Auckland, Dept Pediat, Auckland 1, New Zealand
[3] Johns Hopkins Sch Publ Hlth, Ctr Adolescent Hlth Promot & Dis Prevent, Baltimore, MD USA
[4] Johns Hopkins Sch Publ Hlth, Ctr Injury Res & Policy, Baltimore, MD USA