Changes in head injury with the New Zealand bicycle helmet law

It was claimed that the bicycle helmet law in New Zealand reduced head inju ries to adult cyclists by 28% (Povey, L.J., Frith, W.J., Graham, P.G.. 1999 . Cycle helmet effectiveness in New Zealand. Accident Analysis and Preventi on 31, 763-770). However, the pre-law increase in adults wearing helmets (f rom 30% in 1990 to 43% in 1993) was accompanied by a fall of 45 head injuri es per 100 limb injuries (i.e. - 3.47 for every 1% increase in helmet weari ng) compared with a fall of 11 when wearing increased from 43 to 93% with t he law ( - 0.23 for every 1% increase in wearing). Unless voluntary wearing is 15 times more effective in reducing head injuries, it seems likely that the apparent effects (as described by Povey et al., 1999) were an artefact caused by failure to fit time trends in their model. Such inconsistency of effects over periods of substantial change compared with periods of little change in helmet wearing may be a useful indicator of the presence of tren ds. Because the large increases in wearing with helmet laws have not result ed in any obvious change over and above existing trends. helmet laws and ma jor helmet promotion campaigns are likely to prove less beneficial and less cost effective than proven road-safety measures, such as enforcement of sp eed limits and drink-driving laws, education of motorists and cyclists and treatment of accident black spots and known hazards for cyclists. (C) 2001 Elsevier Science Ltd. All rights reserved.