An evaluation of the methods used to assess the effectiveness of mandatory bicycle helmet legislation in New Zealand.

Mandatory helmet legislation (MHL) was introduced in New Zealand (NZ) in January 1994. Previous studies have shown a significant reduction in cycling head injury associated with MHL; however, one analysis has suggested a diminishing return in head injury reduction with increased helmet wearing rates. The aim of this study is to critically assess the validity of methods and conclusions from studies evaluating the effect of MHL on head injury in NZ. We emphasise the importance of accurately and objectively presenting data and the need for a proper subsequent analysis for valid inference. This plays a paramount role in the communication of research findings as they heavily influence the public perception of road safety and the effectiveness of policy interventions.