Effectiveness of bicycle helmets in preventing head injury in children: case-control study

Thomas S, Acton CH, Nixon J, Battistutta D, Pitt WR, Clark R.
BMJ, 1994;308:173-176.

BRIEF NOTES
This is not a complete Commentary but a summary of observations and criticisms that have been made relating to this paper

Summary of paper (based on authors' abstract)

445 children presenting with bicycle related injuries to two large children's hospitals in Brisbane, Australia took part in a questionnaire-based study. The cases comprised 102 children with injuries to the upper head, the controls were 278 child cyclists with injuries other than to the head or face A further 65 children with injuries to the face were considered as an extra comparison group. Most children (230) were injured after losing control and falling from their bicycle. Only 31 had contact with another moving vehicle. Children with head injury were significantly more likely to have made contact with a moving vehicle than control children. Head injuries were more likely to occur on paved surfaces than on grass, gravel or dirt. Wearing a helmet reduced the risk of head injury by 63% and loss of consciousness by 86%.

General observations

Peer criticism

Based on Towner et al, 2002 :

The circumstances of crashes were different between cases and controls. Head injured cyclists were more likely to have made contact with a motor vehicle, crashed on a hard surface and to have had a bicycle in need of subsequent repair. Thus the two groups are not adequate for meaningful comparison.
It is not clear if unhelmeted children are over-represented in more severe crashes.
The study did not examine injuries to other parts of the body so it is not clear if children with head injury were involved in different types of accident.
Young children are over-represented amongst the controls.
The questionnaire was self-administered and response rates are not given.
Data collection time spans period when helmet legislation introduced. There is no differentiation between pre and post law.
Missing data could potentially cause serious bias in reported results.
Childhood accidents - losing control of bicycle - may be very different to protective effect provided to all age groups.
The degree of damage to the bicycle was used as a proxy to assess the severity of impact.
Question not answered by this study is whether influences leading to non-helmet wearing are associated with other risk taking behaviour.

Conclusion

The study has compared quite different groups of children, lacks important checks on its findings and is not robust. The authors' conclusion that this work justifies legislation to enforce helmet use among children is not valid.

References

Towner et al, 2002

Towner E, Dowswell T, Burkes M, Dickinson H, Towner J, Hayes M, 2002. Bicycle helmets - a review of their effectiveness: a critical review of the literature. Department for Transport Road Safety Research Report 30.