Colin Clarke, a former engineering student, left a comment to my recent post regarding my experiences with Elsevier. Although this post was about an email I sent to Jennifer Mindell (editor in chief of the Journal of Transport and Health) and Chris Pringle (Elsevier Executive Publisher), Clarke took it upon himself to promote his views on bicycle helmets.
Since his comment was really not relevant to my post, I thought about rejecting his comment for quite a while. However, since I assume he would just criticize me somewhere else for censorship, I allowed his comment to be published.
I’ve had numerous online discussions with Clarke about bike helmets (see here, for example). Years ago, it seems Clarke wrote a standard criticism about helmets and, if you’ve ever read one, you’ve essentially read them all. I’ve pointed out fallacies in his arguments many times, and he continually ignores those criticisms.
Clarke’s primary argument is what I call the ‘helmet law as cycling deterrent’ hypothesis. There’s no real, solid evidence to support this hypothesis, yet it has not stopped those like Clarke to proclaim its truth to anyone who cares to listen.
In his comment, Clarke ‘estimates’ (and I’m being generous here) 413 cycling head injuries in NSW are expected in 1992 (this assumes a 30% drop in cycling from 1991 to 1992 and 590 head injuries reported in 1991, i.e., 590*0.7=413). Instead, there were 648 NSW head injury hospitalizations in 1992 (hospital data can be found here).
There are two problems with this approach. First, NSW adults were subject to helmet legislation for the entirety of 1991 and children for half. Clarke would have needed 1990/91 data to make that point (Jan-Dec for adults, Jul-Jun for children). This also assumes there aren’t any existing trends in cycling rates (no data exists to even attempt to estimate those secular trends, except for 1.5 years of pre-law hospital data that doesn’t support Clarke’s hypothesis). Second, if you apply the same logic to arm injuries, you get an expected 660*0.7=462 arm injuries in 1992 (there were 760). In fact, not adjusting for population, head injuries increased by 9.8% while arm injuries increased 15% between those years. None of this suggests Clarke’s hypothesis is true.
Importantly, the injury data comes from a census of medically diagnosed hospitalizations at that time and is therefore of high quality. To justify the drop in cyclists, Clarke relies on repurposed cycling counts from helmet use surveys. Standing on a street corner observing helmet use among cyclists is prone to bias when used as a measure of cycling exposure (this makes the Victoria and NSW helmet use surveys problematic if used for that purpose). Data collected in this way does not readily capture recreational cyclists (which is the backbone of Australian cycling) and does not/cannot account for changes in cycling routes or patterns (observation locations are fixed from year to year). It is known that many kids stopped cycling to school in Australia because either their parents or their schools started discouraging it or outright forbade it. This was not due to helmet legislation, although the two issues may share a common causal factor (i.e., parents/society concerned about cycling injury). This did not mean kids stopped cycling after school or on weekends.
Data collected through (stratified) random sampling does not suffer from those problems. The only such surveys in Australia, that I’m aware of around the time of helmet legislation, are from South Australia and Western Australia. Below is a summary of their results for proportion of responses to one of four categories of cycling frequency. (Note these reports do not seem to exist online and I’ve decided to host them on my webpage as I feel very few have ever read them or any other source material.)
|South Australia||Western Australia|
|At least weekly||21.8||21.0||At least weekly||26.6||27.7|
|At least monthly||5.2||6.0||At least every 3 months||11.1||11.6|
|At least every 3 months||3.9||4.4||At least once per year||10.3||11.5|
|Less often or never||69.1||68.6||Never||52.0||49.2|
The results indicate no change in cycling in either SA or WA. We also found that to be true for non-head cycling injury hospitalisations in NSW. Neither arm nor leg injuries declined significantly following helmet legislation, and certainly not at the 20% rate cited by Clarke or the 30-40% figure quoted by others. If cycling in NSW dropped substantially after helmet legislation as suggested, I have always wondered why is there no evidence in the census of injury hospitalizations?
Clarke cites two of his own papers to justify his position. The first is a non-peer reviewed conference paper titled Evaluation of Australia’s bicycle helmet laws. I received numerous spam emails about this conference for months. Unfortunately, I get 10+ emails a day for such conferences or predatory publishers asking me to submit ‘my latest research’. Legitimate conferences and publishes do not need to advertise so aggressively.
As with much of his comments about other people’s work, Clarke’s paper is loaded with cherry-picked data and not a shred of statistical/analytic rigor. I’ll detail a few examples.
Figure 3 on page 6 are counts of cyclists from helmet use surveys in Victoria in 1990 and 1991. Back in June 2013, Tim Churches pointed out this figure omits the 1992 data and does not aggregate by age, which is important considering cycling numbers differ substantially across age groups. Below is a plot created using Tim’s R code.
The counts of cyclists for two age groups are virtually identical from 1990 to 1992 (age 5-11 and 18+). The only decline was for 12-17 year olds. If you assume this data is an accurate estimate of cycling exposure (keep in mind I don’t agree with this stance), the cycling decline is age dependent and not true overall.
Clarke also cites a WA report from Heathcote. I could not find a copy of this 1993 report anywhere; however, I did find a 1994 report by the same author. According to 1994 report, the 1993 report concerned helmet use and “recommended the need for further research into cycling trends, and attitudes towards the helmet wearing law”. This was the motivation behind the 1994 report. Therefore, the later report is the more relevant here.
The numbers of recreational cyclists reported by Clarke are not found in the 1994 report; however, Table 8 summarizes Usual Destinations with 21.3% in 1989 and 17.4% in 1993 reporting “To a venue for sport/recreation”. This is not near a 57% reduction in recreation cycling as reported by Clarke and, when taken out of context, ignores that there was no real change in WA cycling frequency as was reported in the same surveys (see above table).
In his Table 13, Clarke reports proportions cycling to work in five year intervals (I discussed problems with how this data is interpreted in a previous post). In addition to the usual problems with this data, Clarke creates additional problems by “estimating” the proportion in 1990. He gives absolutely no justification for this figure except for links to anti-helmet advocacy websites. I guess he could have extrapolated that figure, but such an estimate would be fraught with problems from data taken over three days 5 years apart. Estimating trends from such data completely ignores day-to-day variability.
Clarke also cites his 2012 NZMJ paper. Note I have been critical of this paper on at least four occasions [4-7]. The last citation was a systematic review of the methods used to assess the New Zealand bicycle helmet law. Against quality criteria for assessing a population-based intervention, Clarke’s study scored the lowest of five included studies.
Clarke is quite active on the internet sharing his views on helmet legislation. This includes routine editing of the Wikipedia pages on bicycle helmets under the pseudonym “Colin at cycling” where his contributions have been to promote his NZMJ paper (see the edits page). Although I’m generally supportive of Wikipedia (even contributing money), I find it disturbing anti-helmet advocates like Clarke have taken control of the bicycle helmet content. Like Clarke, they all have conflicts of interest which are never reported (see Dorothy Robinson’s Wikipedia page for a flavor of what’s happened, she has a clear conflict of interest since she essentially promotes her own work and strongly opposes the inclusion of other studies that criticize her work).
If anything, Clarke is steadfast in his beliefs helmets are ‘bad’ and he’s not afraid to share his views. However, I’d be more willing to accept his points if he’d stop cherry-picking data and present a balanced view of the topic. My past experiences with him indicate that is highly unlikely.
- Marshall, J. & White, M. (1994). Evaluation of the compulsory helmet wearing legislation for bicyclists in South Australia. South Australian Department of Transport, Walkerville, SA.
- Heathcote, B. & Maisey, G. (1994) Bicyclist use and attitudes to the helmet wearing law. Traffic Board of Western Australia, Perth.
- Walter, S.R., Olivier, J., Churches, T., & Grzebeita, R. (2011). The impact of compulsory cycle helmet legislation on cyclist head injuries in New South Wales, Australia. Accident Analysis and Prevention, 43, 2064–2071.
- Olivier, J. (2012) Don’t blame mandatory helmets for cyclist deaths in New Zealand. The Conversation.
- Wang, J., Olivier, J. & Grzebieta, R. (2014). Response to ‘Evaluation of New Zealand’s bicycle helmet law’ article. The New Zealand Medical Journal, 127, 106-108.
- Olivier, J., Wang, J.J.J., Walter, S. & Grzebieta, R. (2014). Anti-helmet arguments: lies, damned lies and flawed statistics. Journal of the Australasian College of Road Safety, 25, 10-23.
- Olivier, J., Wang, J.J.J. & Grzebieta, R. (2014). A systematic review of methods used to assess mandatory bicycle helmet legislation in New Zealand. Journal of the Australasian College of Road Safety, 25, 24-31.