Celebrity Blogger Gets Helmet Research Wrong

I received a phone call last week from Nick Rushworth from Brain Injury Australia. He was in a rush and wanted to know if some comments made earlier in the day on 2UE had any validity. I was on my way to a meeting, so I flicked him links to websites and some journal articles to read. When I got some free time, I looked into what all the fuss was about. Celebrity blogger Sarah Wilson was telling 2UE listeners to get rid of the Australian bicycle helmet laws. She has also blogged about bike helmets on her website and contributed an article to the Daily Telegraph. After listening to her interview and reading her blog, I recommend Sarah Wilson do some fact checking before doling out recommendations.

Let me explain. To support her argument, Wilson states

…biggest stumbling block to getting people to riding is not the sweat, is not the exertion, it’s the bike helmets.

In 2011 and 2013, the Cycling Promotion Fund published survey results in which participants were asked about barriers to cycling. In the first report, helmets were the 10th and 13th most common response for current cyclists and non-cyclists respectively, and helmet wearing comprised 4% of all responses. When asked about encouraging women to cycle more in the later survey, 4.1% of responders gave the repeal of the helmet law as their main response. The most common barriers from both surveys were lack of cycling infrastructure and concerns around safety. Neither sweat nor exertion made either list as a cycling barrier.

Wilson also seems to claim Australia and New Zealand are the only countries with helmet legislation and other countries have rescinded their laws. There are helmet laws in various parts of the US and Canada as well as Dubai, Finland, Spain, Iceland, Czech Republic, Jersey and Japan. It has also been debated in other countries. More information can be found here. Note that most helmet laws outside of Australia and New Zealand are directed at children only. I do believe Israel and Mexico City repealed helmet legislation, but that doesn’t appear to be the norm as suggested.

During the interview, Wilson also indicated the science around helmets are not supportive of their use. She gives more details on her website and this is where her argument really starts to fall apart. First up is the argument helmet laws deter cycling. I’ve blogged about this before and discuss it more fully in a peer-reviewed article published last year. In short, this argument is only supported when cherry-picking through the available data. The data often used are cycling counts from helmet use surveys which have a clear selection bias. To my knowledge, there are only two surveys (data collected before and after legislation) that even attempt to collect a representative sample (one from South Australia and the other Western Australia). Here is a summary of the proportions cycling in a given time frame from those surveys. Cycling amounts are nearly identical before and after helmet legislation in those Australian states.

South Australia Western Australia
1990 1993 1989 1993
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

Wilson then argues for safety-in-numbers or Smeed’s Law. There certainly is research that has found a negative association between cycling numbers and injuries per cyclist when comparing jurisdictions. However, there is no evidence of a dose response, i.e., cycling numbers increase and injuries per cyclist then decreases. I’ve blogged about this using NSW data here — as cycling participation increased in NSW, cycling injuries increased at a similar rate.

Wilson does correctly note there are no randomised controlled trials assessing the effect of bicycle helmets to mitigate head injury.There is a quite obvious reason for that — researchers are not ethically allowed to randomly assign cyclists to wear/not wear a helmet, instigate a bicycle crash and then clinically diagnose injury and severity. Observational study designs, like case-control studies, are the only real option here where participants self-select to a treatment (helmet) or control (no helmet).

Wilson then cites a Sydney Morning Herald article and later references an article in the Journal of the Australasian College of Road Safety by Chris Rissel (these are related) as evidence helmet legislation doesn’t work in Australia. Wilson doesn’t appear to be aware the Journal later retracted Rissel’s paper because the article contained serious data errors among other issues. Note the SMH article does link to a correction where Rissel admits to the errors. Part of the issue is evident from Table 2 of Rissel’s paper as the age specific totals do not add up to the all age total. It is also evident when plotting head injury counts by year (raw and ‘corrected’ by summing across age groups) compared to counts I published three years later in another journal (note Rissel’s data is aggregated by financial year and mine is by calendar year). NSW_Head_Inj The head injury counts rise rapidly from 1997/98 to 1998/99. This is the year the NSW Department of Health changed their coding practices from ICD-9-CM to ICD-10-AM. There usually are discrepancies between ICD versions; however, this amounted to about 10 cases per year when both codes were used. My guess is that Rissel made two errors — head injuries were not coded properly for ICD-10-AM years and those incorrect codes were incorrectly mapped to ICD-9-CM. Simply put, the data in Rissel’s retracted article are wrong and therefore no valid conclusions can be made from them.

Next up, Wilson makes a very shocking claim. She writes

Helmets have been shown to prevent injury from “linear speeding”. But many accidents occur from “angular” accidents caused when the head is rotated. Helmets actually CAUSE head rotation.

There is absolutely no evidence helmets exacerbate rotational injuries. I’ve blogged about it here and below is a summary for a paper published last year (the citation numbers correspond to the article).

 Curnow [26, 27] suggested helmets exacerbate rotational injuries; the more serious being diffuse axonal injury (DAI). Although Curnow only hypothesised the DAI/helmet link unsupported by any real world or experimental evidence, some have taken this as fact [11, 13, 42, 94, 82, 83, 14]. There is, however, no existing evidence to support the DAI hypothesis. McIntosh, Lai and Schilter [61] found, when testing oblique impacts on dummies to simulate head rotation, helmet wearing did not increase angular acceleration, a result unsupportive of Curnow’s hypothesis. In a study by Dinh et al. [34], using trauma registry data from seven Sydney area hospitals over one calendar year, 110 cyclists were identified and none were diagnosed with DAI regardless of helmet wearing. Walter et al. [110], using linked police and hospitalisation data in New South Wales (NSW) from 2001-2009, reported at most 12 possible DAI cases out of 6,745 cyclists in a motor vehicle collision. Seven of the twelve cyclists were unhelmeted. These results suggest the incidence of DAI among cyclists appears to be rare and unrelated to helmet wearing. Additionally, computer simulated studies of bicycle crashes found no evidence helmets increased the likelihood of neck injury among adults [63] nor was there evidence helmets increased the severity of brain or neck injury in children [62].

The arguments against helmets presented by Sarah Wilson are not supported by available evidence. To close she does link to anti-helmet websites like Cyclist Rights Action Group and Helmet Freedom who seem to have supplied her with information. She also regurgitates information by anti-helmet advocate Paul Martin whose only ‘research’ on this topic, as far as I know, is a an anti-helmet commentary published by MJA in 2011. He may be a physician, but he doesn’t appear to be a researcher.

As a bit of a side issue to the science around bike helmets, Wilson also makes a civil liberties argument. In my view, that is her only valid argument. Any time an individual’s rights are taken away in the name of the greater good, it should be vehemently challenged by the populace and only accepted with a majority approval. A 2012 Australian survey estimates 96% approve of helmet legislation. On the other hand, I have colleagues who make the argument those with avoidable head injuries are a steep cost to countries like Australia where medical costs are shared. I find both arguments quite compelling and perhaps that’s where the debate around bike helmets should lie.

Note: The discussion and links to Chris Rissel’s retracted JACRS paper have been removed from Sarah Wilson’s blog.