RT Journal Article SR Electronic T1 Helmet laws and health JF Injury Prevention JO Inj Prev FD BMJ Publishing Group Ltd SP 170 OP 171 DO 10.1136/ip.4.3.170 VO 4 IS 3 A1 Dorothy Robinson YR 1998 UL http://injuryprevention.bmj.com/content/4/3/170.abstract AB