Intended for healthcare professionals

Rapid response to:

Analysis And Comment

No clear evidence from countries that have enforced the wearing of helmets

BMJ 2006; 332 doi: https://doi.org/10.1136/bmj.332.7543.722-a (Published 23 March 2006) Cite this as: BMJ 2006;332:722

Rapid Response:

Is overall safety compromised by helmet use?

Diane Thompson replying to Richard Keatinge (8 July) says "Your claim
that there is differential reporting of helmet use by head injured (cases)
and non head injured (controls) cyclists in published case-control studies
is mere speculation." This seems rather surprising because Rivara et al.
stated "one study that compared observations of helmet use to a statewide
telephone survey found that the survey overestimated helmet use by 15 to
20 percentage points".[1] Thompson’s comment that "There is good evidence
that self-reported helmet use is accurate" seems to be at odds with a
paper she co-authored.

As Dr Keatinge pointed out, potential biases in estimates of helmet
wearing are important because the benefits Ms Thompson and colleagues
claim for helmets depend on the validity of comparing helmet wearing of
head injured cyclists treated at emergency departments with a community
control group who fell off their bikes. Because of the difficulty finding
adults who crashed or fell off their bikes, 86% of the community controls
(CC) were children under 15.[2] At the time, a large observational survey
in Seattle showed that 3.2% of child cyclists wore helmets, compared to
21.1% of children in the CC group.[3]

If, as Ms Thompson suggests, these helmet wearing rates are correct,
it would seem that helmeted children fall off their bikes 7 times more
often than non-wearers. There would be no point in recommending helmet
wearing, because helmet wearers seem to have many more injuries than
non-wearers.

Why should helmet wearers have more accidents? Clarke details how
helmet use can lead to more head impacts plus additional accidents.[4]
Thompson's approach to helmet research appears to assume that differences
in head injury rates were due to helmets. This may appear reasonable, but
in practice there are many complications to consider.
For example, from 1988-1992, head injuries of vehicle occupants, motor
cyclists and pedestrians fell by 56% in South Australia.[5] If head injury
rates can change by such an extent over a 4-year period because people
take greater care and do not speed or drink drive, is it not possible that
the head injury rate for cyclists can also change
substantially without any effect of helmets? The injury rate for cyclists
varies from country to country and with the type of cyclist. The head
injury rate is also a function of the ratio of head injury to other
injuries and there is evidence that helmet use tends to increase the
overall accident rate, effectively changing the head injury rate.

A major problem with case-control studies is that they have no means
of measuring the overall accident rate. If subjects were assessed on how
much cycling they do, we could calculate head and other injury rates per
unit time, a much better approach than just considering numbers or
proportion of head injuries. It is time to move forward with helmet
research and consider the effect on balance and riding stability, as well
as looking at the best ways to reduce accidents, promote cycling and allow
for personal choice.

1 Rivara FP, Thompson DC, Patterson MQ, Thompson RS, Prevention of
bicycle-related injuries: Helmets, Education, and Legislation, Annu Rev
Public Health, 1998. 19:293-318.

2. Thompson, R. S., F. P. Rivara, et al. A case-control study of the
effectiveness of bicycle safety helmets. N Engl J Med 320(21), 1361-7,
1989

3. DiGuisseppi, C. G., F. P. Rivara, et al. Bicycle helmet use by
children. Evaluation of a community-wide helmet campaign. JAMA 262, 2256-
61, 1989.

4 Clarke CF, The Case Against Bicycle Helmets and Legislation, World
Transport Policy & Practice Volume 12 No. 3. 2006
http://www.ecoplan.org/wtpp/wtj_index.htm

5 North B, Oatey P, Jones N, Simpson D, Head injuries from road
accidents - a diminishing problem?, Med J Aust, Vol 158 March 15, 1993.

Competing interests:
None declared

Competing interests: No competing interests

25 July 2006
Colin F Clarke
Hon Sec CTC Yorkshire and Humber Region
York YO41 1BU