Journal of Transport and Health and Publication Bias?

Scientific journals exist as an outlet for the promotion and discussion of scientific ideas and and the presentation of evidence that can support or not support such ideas. This is a crucial aspect of scientific discourse as it allows for the dissemination scientific research to a wide audience (even if that research is not understood by the populace). Otherwise, for example, Gossett’s (aka student) t-test might only have been known to those taking a tour of the Guinness brewery at St James’s Gate (however, I can attest that the best milieu for discussing statistics is over a few beers).

The peer-review process is used to decide what gets published and what does not as judged by one’s scientific peers. Importantly, those contributing to the peer-review process should check their personal biases at the door and judge the quality of the evidence presented. This is, generally speaking, the mantra of the highly respected Public Library of Science (PLoS) journals.

This brings me to the Journal of Transport and Health (JTH), a new Elsevier journal which published its first issue this month. The journal is officially affiliated with the Transport and Health Study Group (THSG) which has as one their policy objectives “To promote a more balanced approach to cycle safety and oppose cycle helmet legislation.” On the THSG website, is an article that questions the use of even promoting helmet use by way of the common Straw Man argument that motor vehicle drivers and passengers should also be compelled to wear helmets. This argument ignores the many safety features of modern motor vehicles that aren’t even possible on a bicycle. Think about it this way, if I turn the argument around a bit to state “Why mandate airbags (or insert any other safety feature) for cars since we don’t make them mandatory for cyclists?” Is that a valid argument?

As you would expect, the editorial board of the JTH is littered with members of the THSG (it’s their journal, so why not?). Below is a list of JTH editorial board members and their role in the THSG (thanks goes out to Tim Churches for supplying the information in this table). This is as far as can be discerned from their website and I suppose it’s entirely possible others could simply be members of the THSG.

Name Institution JTH role THSG role
J. Mindell University College London (UCL), London, England, UK Editor-in-Chief Co-Chair
S. Alvanides Northumbria University, Newcastle, England, UK Associate Editor Executive Committee
A. Davis University of the West of England, Bristol, UK Associate Editor Executive Committee
S. Gray University of the West of England, Stapleton, Bristol, England, UK Associate Editor Executive Committee
S. Handy University of California at Davis, Davis, CA, USA Associate Editor
R.A. Kearns University of Auckland, Auckland, New Zealand Associate Editor
T. Sugiyama Baker IDI Heart and Diabetes Institute, Melbourne, VIC, Australia Associate Editor
L.B. Andersen University of Southern Denmark, Odense, Denmark Editorial Board
J. Dill Portland State University, Portland, OR, USA Editorial Board
R. Ewing The University of Utah, Salt Lake City, UT, USA Editorial Board
L. Frank University of British Columbia, Vancouver, BC, Canada Editorial Board
J. Hine University of Ulster, Newtownabbey, UK Editorial Board
S. Inoue Tokyo Medical University, Tokyo, Japan Editorial Board
L.R. Int Panis Flemish Institute for Technological Research (VITO), Mol, Belgium Editorial Board
R. Mackett University College London (UCL), London, UK Editorial Board Executive Committee
C. Perez Agencia de Salut Publica de Barcelona, Barcelona, Spain Editorial Board European Committee
J. Pucher University of North Carolina at Chapel Hill, Chapel Hill, NC, USA Editorial Board
C. Rissel The University of Sydney, NSW, Australia Editorial Board
L. Rizzi Pontificia Universidad Católica de Chile, Santiago, Chile Editorial Board
D. Rodriguez University of North Carolina at Chapel Hill, Chapel Hill, NC, USA Editorial Board
H Rutter London Sch. of Hygiene & Tropical Medicine, London, England, UK Editorial Board
J.F. Sallis University of California at San Diego (UCSD), San Diego, CA, USA Editorial Board
Y. Shiftan Technion – Israel Institute of Technology, Haifa, Israel Editorial Board
N. Silverstein University of Massachusetts at Boston, Boston, MA, USA Editorial Board
M. Wardlaw Edinburgh, Scotland Editorial Board Executive Committee
S. Watkins Stockport Metropolitan Borough Council, Stockport, England, UK Editorial Board Co-Chair

What is surprising here is the lack of balance on the editorial board — there are no members who could provide counterpoint to the anti-helmet views of the THSG. Non-THSG editorial board members include Chris Rissel who is an outspoken advocate against bicycle helmet legislation (see here, for example). Another JTH editorial board member, Malcolm Wardlaw, is an editorial board member of the anti-helmet website Bicycle Helmet Research Foundation (by the way, I’m  not convinced just anyone with a gripe can legitimately establish an editorial board). I searched for Wardlaw on the academic search engine Scopus (also published by Elsevier) and I found 12 documents — 10 seemed to be commentaries against helmets, one is a magazine article, and one seemed to be an original research article.

What really concerns me is this — will a paper that says anything positive about helmets or helmet legislation (and backed by evidence) be peer-reviewed without the biases of the THSG influencing the decision to publish? Also, will authors shy away from citing peer-reviewed articles that demonstrate evidence supportive of helmets or helmet laws? Will reviewers insist on citing anti-helmet arguments that have no evidence base like the DAI hypothesis? This is important as selective citation seems to be common practice when publishing on this topic.[1]

The very first issue contains commentaries from the Editor-in-Chief Jennifer Mindell (also co-chair of the THSG) and another by Stephen Watkins (the other co-chair of THSG). On page 3 of the very first issue of JTH, Watkins states[2]

“We still find ourselves having to fight defensive campaigns, such as resisting proposals for compulsory cycle helmets which will do little for cycle safety but will have a serious adverse effect on cycling levels, not least because they feed misconceptions about cycle safety.”

This comment is not surprising as Watkins has also been openly critical of the Spanish government for concluding (original in Spanish, translated with the help of Google) “the scientific evidence of the decrease of morbidity and mortality due to the helmet use by cyclists is absolutely conclusive.” This makes me wonder if an article submitted to JTH would be outright rejected for such a comment even if supported by evidence.

As far as I can tell, the only justification given for the THSG’s position on bicycle helmets comes from this presentation. In this presentation, Mindell, Wardlaw and Franklin discuss a paper I co-authored.[3] Regarding trends in cycling injuries around the NSW helmet law, the authors present this graph

MindellHead

and state

“It has repeatedly been claimed that such improvements have occurred. But to date, not a single such claim has stood the test of close inspection. In New Zealand, promotion and legislation increased helmet wearing to nearly universal use, yet there is no noticeable improvement in the %HI trend for cyclists (red) relative to the control (black). In NSW, ratios of head to arm and head to leg injuries were compared before and after the helmet law. The helmet law rapidly increased the helmet wearing rate from about 20% to 80%. But again, it is difficult to discern any particular reduction in head injuries to cyclists (red) compared with pedestrians (blue), although the data are rather “noisy”.”

A similar argument is also presented by the BHRF, an anti-helmet advocacy group. A major problem with this plot is it doesn’t actually correspond to the plots or the data we used in our paper, as discussed elsewhere.[4] Instead, both time series plots have been rescaled and shifted so they overlap and are therefore not comparable (this is evidenced by the lack of units on the y-axis). This plot, by itself, is also problematic as the trend in either head or arm injuries are unclear. Considering this plot and the comments made by the authors, I wonder if they understand what “noisy” means in this context.

Time series data, when finely aggregated, can usually follow an up-and-down pattern. This is not necessarily random variability (or “noise”), but can be cyclical or seasonal patterns in the data. For example, there may be more cycling injuries during summer months and less during the winter (due to more or less cycling). This can be modeled or removed prior to analysis (as we did in our original paper). The amount of scatter around the fitted model gives us a measure of “noise”. In our analysis, we found very little “noise” relative to the effect of the helmet law.

The appearance of the “up-and-down pattern” can be lessened by aggregating the data at a higher level (e.g., quarterly or yearly). This is usually not a good idea for the analysis due to the reduction in efficiency (in this case, the number of time points would decrease from 36 to 12 for quarterly aggregated data). Below is a plot of the head and arm injury data when aggregated by month, quarter and semester (the data can be found here and courser aggregations were computing by averaging monthly injury rates over 3 and 6 month periods).

NSW-Head-Arm

It is clear that as the aggregation gets courser, the apparent noisiness disappears. It is also clear there was a profound change in head injury from the third to the fourth semesters which correspond to either side of the helmet law. As I stated before, it would be unwise to analyze the semesterly data (there are only six time points and the full model estimates eight parameters), but it may be useful to visually present data in this manner to non-statisticians to avoid confusing systematic with random variability. My guess is our paper would’ve been rejected by the JTH editors due to an apparent lack of statistical understanding — whether biased against helmets or not.

With those issues in mind, I wonder whether an anti-helmet advocacy group should be in charge of a scientific journal? I have written several original research articles and commentaries regarding the evidence around bicycle helmet legislation. Since much of my work has demonstrated positives, I’ve been labeled as “pro-helmet” by some. I find this categorization disturbing as I don’t ever set out to demonstrate helmets or helmet laws are beneficial. It always comes down to drawing scientific conclusions from performing rigorous analysis using the best available data. If I find strong evidence to the contrary, I will adjust my views accordingly, as would any scientist. However, I’m not convinced any of my research would be given a fair shake at the JTH.

This is my opinion and I could certainly be mistaken. What is your take on this journal?

  1. Olivier, J. (in press) . The apparent ineffectiveness of bicycle helmets: A case of selective citation. Gaceta Sanitaria. 
  2. Watkins, S.J. (2014). The Transport and Health Study Group. Journal of Transport & Health, 1, 3-4.
  3. 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.
  4. Olivier, J., Grzebieta, R., Wang, J.J.J. & Walter, S. (2013). Statistical Errors in Anti-Helmet Arguments. 2013 Australasian College of Road Safety Conference – “A Safe System: The Road Safety Discussion” Adelaide.

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13 thoughts on “Journal of Transport and Health and Publication Bias?

  1. Jake,
    really good article! You make some very salient points concerning the make up of the JTH Editorial Board and the bias we can expect from any articles sent to this journal that will be in conflict with THSG’s policies. I am surprised that Elsevier have overlooked (allowed?) what is an obvious conflict of interest between JTH and THSG associated board members.

    Fancy Elsevier being associated with a transport health promotion group that has as its number two policy statement “To promote a more balanced approach to cycle safety and oppose cycle helmet legislation”. Opposing cycle helmet legislation is a balanced approach? Are they serious? I thought scientific research was meant to be independent of any policy advocacy.

  2. No one is without their own biases, and as a researcher worth their salt one tries to be as aware of those biases as possible, and to minimise their influence on research. With a diverse editorial board, the possibility of an individual’s personal bias having an impact is minimal. However, the more that individual biases align, the greater possibility for them to have an effect on what gets through and what doesn’t, even if this is not intended. At face value it seems that JTH is at risk of this to a greater extent than other journals. It may well be that all JTH editors are the epitome of balance and integrity, but the question marks outlined in this post would make me hesitate to submit there until my concerns were shown to be unfounded.

    • To save space here, I refer you to my letter printed in Injury Prevention: http://injuryprevention.bmj.com/content/20/4/292.full?sid=72a19660-cc6e-4d22-b765-ffb0bc1fad6a And also to the Editor’s note at the end of Watkins’s article on the THSG (which, incidentally, is the first of many such articles about organisations that aim to connect transport and health; one on the TRB’s Transportation and Health subcommittee was published in issue 2 and one on Transport-Public Health Link will be published in a future issue).

      In summary, many journals are associated with organisations but the society does not influence the journal. The BMJ does not take note of BMA policy. I was aware of Malcolm Wardlaw’s position on helmets. Even if I had known of Chris Rissel’s opposition to helmets or that Robin Kearns is a passionate advocate for cycle helmets, it would not have affected Elsevier’s invitations to them to be on the Board (and in Robin Kearns’s case, be one of the Associate Editors). The journal has no policies, other than to publish high quality, relevant, research. The Aims and scope of the journal can be found at http://www.journals.elsevier.com/journal-of-transport-and-health

      Papers are accepted by JTH on two criteria only: is it relevant to the scope of the journal and is it of high enough scientific quality? I urged Jake Olivier and Tim Churches to submit their recent review to JTH, but they declined.
      The THSG is an evidence-based organisation; it’s policies are based on its understanding of the current evidence. As the evidence changes, so the policies are reviewed.
      I have been trying to organise a scientific debate in JTH, in which people play ‘the ball not the man’, so that those who have studied the evidence and concluded that helmets are protective and/or that helmet laws have an overall positive effect on health can debate the strength of and potential flaws in the evidence with those who have studied the evidence and concluded the opposite. I suggested that these were not peer-reviewed, to avoid even the possibility of reviewers using prior bias and views in their comments, other than the authors from the two sides of the debate commenting on each others’ articles and on those comments, with other researchers not know for holding particular views on the subject commenting, again, in public. I also confirmed that if the debate demonstrated that the THSG was wrong in its assessment of the evidence, the policies would be reviewed to reflect our changed understanding.
      I feel strongly that these issues need to be discussed in a respectful way in a scientific forum, rather than in a series of confidential emails full of allegations or in separate blogs, with difficulty in bringing all the evidence together in one place. Unfortunately, I have not yet found anyone who believes that the evidence supports the value of helmets and/or helmet laws and is willing to take part in this debate. Any volunteers?
      P.S. The JTH has published no articles on cycle helmets. None have been submitted.

      • Jennifer,

        Thank you for your reply and supplying more information about the JTH.

        However, I think it’s important that I clarify a few points.

        First, it is true you sent me an invitation to submit to the JTH a conference article I had recently published unless they were already under review elsewhere. I thanked you for your invitation and declined because this work had already been submitted elsewhere. I was actually working on the revisions today and hope to resubmit soon.

        Secondly, you indicate you want the issues around helmets or helmet/laws “discussed in a respectful way in a scientific forum”. However, your actions indicate otherwise. I first heard about you and the THSG when I came across slides authored by you, Malcolm Wardlaw and John Franklin critical of helmets that was presented at a 2011 THSG seminar. As I discussed above, your criticisms were unfounded. As this relates to your comment, neither you or your co-authors contacted me or any of my co-authors about our paper. None of us were invited to have an open discussion about the evidence, or lack thereof, surrounding the helmet issue. I had no contact with you prior to the end of 2013.

        I am also not encouraged by the inclusion of Malcolm Wardlaw or Chris Rissel to your editorial board. Since 2000, Wardlaw has 12 documents on Scopus of which 10 are commentaries critical of helmets and another is a magazine article. Even if his comments were somehow supportive of helmets, how can you appoint someone with one career scientific article to the editorial board of a peer-reviewed journal? There’s no evidence there that he knows what high quality research looks like.

        Perhaps it is important to one day have a discussion in a scientific journal where the merits of helmets and helmet laws are discussed in a polite and open manner. I have still have serious concerns if it were to happen in the pages of the JTH.

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  5. Dear Jake,

    As the Executive Publisher at Elsevier responsible for the management of the Journal of Transport & Health, I should like to respond to your comments about it.

    JTH is not “their [THSG’s] journal”. It is Elsevier’s journal. The affiliation between JTH and THSG simply recognizes that the journal’s focus on “research on the many interactions between transport and health” is congruent with THSG’s overarching purpose of “understanding and addressing the links between transport policies and health and promoting a healthy transport system”, and that individuals interested in the activities of THSG are likely to be interested in the content of JTH, and vice versa. Affiliation with (or indeed membership of) THSG does not necessarily imply endorsement of all 20 of its stated policies.

    A similar mistaken conflation was recently published in Injury Prevention 2013; 19:325. I am happy to say that the editor of Injury Prevention duly apologized and published Dr Mindell’s letter of correction:
    http://injuryprevention.bmj.com/content/early/2014/03/07/injuryprev-2014-041194.full .

    Nevertheless, I can understand why those who disagree with THSG policies might be concerned at the strong THSG contingent on the editorial board of JTH. I believe such concerns are unfounded, as I am confident that JTH’s editorial team handles all papers submitted to the journal impartially. In fact, Dr Mindell has been putting considerable effort into commissioning a special collection of papers for JTH devoted to the contentious topic of cycle helmet legislation, explicitly so that evidence pro and con can be presented and discussed objectively and scientifically.

    Having said that, Dr Mindell and I accept your point about the need for more balanced representation on the editorial board. I hope that we will be able to make suitable appointments to reassure you in the near future.

    Meanwhile, I invite you to submit your work to JTH and test the objectivity of its editorial process yourself.

    Kind regards,
    Chris

    Chris Pringle, MILT
    Executive Publisher – Geography & Transport
    Elsevier
    Langford Lane
    Kidlington OX5 1GB
    United Kingdom

    Tel.: +44 (0)1865 843712
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    • Chris,

      I’m confused by part of your post. Regarding an opinion published in Injury Prevention regarding the JTH, you state “the editor of Injury Prevention duly apologized”. I do see that the Injury Prevention editor allowed Jennifer Mindell to clarify what she believes are “inaccurate statements”. However, this doesn’t appear to be an apology.

  6. I will leave it to my colleagues to respond to the comments from Jennifer Mindell and Chris Pringle, above. However, I would like to respond to the following statement made by Dr Mindell in defence of the tight nexus between THSG and the JTH: “In summary, many journals are associated with organisations but the society does not influence the journal. The BMJ does not take note of BMA policy.”

    Yes, it is true that the British Medical Association has policies, and no, those policies don’t affect the editorial policies or decisions of the British Medical Journal, which the BMA publishes. But a key difference is that office bearers and policy-makers in the BMA are NOT the same people as the editors and editorial staff of the BMJ. If the THSG merely auspiced the JTH, and the editors and editorial board of the JTH were demonstrably independent (that is, not the very same people), then we, and probably other researchers, would be much more sanguine about submitting manuscripts to the journal. Unfortunately, that is not the case. Jennifer Mindell, Stephen Watkins and other THSG office-bearers who are also on the JTH editorial staff or editorial board have a clear conflict of interest between the THSG policies and JTH editorial independence, and that conflict of interest cannot be managed merely by asserting that one doesn’t affect the other, when it clearly does, as evinced by the selection of people for the JTH editorial board (which is clearly biassed against helmets, as Chris Pringle himself admits in his comment above).

  7. In observing that Wardlaw has published one “scientific article”, A/Prof Olivier appears to be referring to Wardlaw’s 2000 BMJ article (http://www.ncbi.nlm.nih.gov/pubmed/11124188), which is far from “scientific” and bursting with errors, misrepresentations and omissions. Wardlaw devotes 500+ words (a substantial proportion of the article) to an extremely unscientific waffle that starts with:

    “It began in America, as so many trends do, but for years no one in Europe took any notice. American tourists wearing helmets around the streets of London first drew media attention. And although public response to walking helmets was initially amusement, the appeal of extra safety drew some pioneers to the habit, especially academics and competitive walkers. The first case-control study of about 2000

    Some of the errors, misprepresentations and omissions in Wardlaw’s (2000) “scientific article” . . .

    Wardlaw claims that Scuffham’s (2000) analysis included “superficial” injuries. The 2nd sentence of Scuffham’s abstract states that “the study population consisted of three age groups of cyclists . . . admitted to public hospitals”. Wardlaw has a BSc (Hons) in aeronautical engineering, and an MBA, and apparently qualifications/experience relevant to assessing helmet/law research. It seems that Wardlaw is not aware that whilst “superficial” injuries may be treated in a hospital emergency department, it would be EXTREMELY rare for patients with (only) “superficial” injuries to be ADMITTED.

    Wardlaw cites Robinson’s 1996 article to support his claim/s that “Experience shows helmets give only limited head protection. Studies in Australia show some prevention of superficial injuries (such as scalp lacerations) but only marginal prevention of “mild” head injuries and no effect on severe head injuries or death.”. The data corresponding in Robinson’s tables 2 and 3 shows that cyclist head injury hospital ADMISSIONS in NSW and Victoria fell by considerably more than cyclist non-head injury hospital admissions.

    In the Victorian (Carr) data, only 1 of 2404 cyclist head injury hospital admissions in Victoria was AIS 1 (minor, eg. “superficial laceration”, (http://en.wikipedia.org/wiki/Abbreviated_Injury_Scale). The Carr data also shows that the number of cyclist serious/severe head/brain injury hospital admissions dropped by 60%, when for the same period the number of cyclist non-head injury admissions (and pedestrian head injury admissions) dropped by (only) 20%.

    As a (THSG and JTH) colleague of Wardlaw’s, perhaps Dr Mindell can cite the evidence (in Robinson’s article) which shows that “helmets give only limited protection. Studies in Australia show some prevention of superficial injuries (such as scalp lacerations) but only marginal prevention of “mild” head injuries and no effect on severe injuries or death.

    Wardlaw also misrepresents the results of the Hendrie study as showing that “head injuries are only 11% lower than would be expected with helmets”. Hendrie et al. in fact noted that the reduction in head injuries (in WA) was “between 11 and 21%” (as noted by Hynd, analyses that do not take injury severity into account will underestimate the true helmet effect, another fact that Wardlaw is/was apparently unaware of).

    The Hendrie study cites the Carr (Vic), Williams (NSW) and Marshall (SA) studies, however these studies are not mentioned by Wardlaw. Williams estimated that during it’s first 4 years, the NSW helmet law was responsible for savings of almost $48M in (SERIOUS) road casualties. The injury data in the Marshall also study shows that cyclist head injury hospital ADMISSIONS reduced by considerably more than cyclist non-head admissions.

    Wardlaw cites Dorothy Robinson’s 1996 article, and an article by Bruce Robinson as ‘showing’ that cycling “fell by 35%”. The data in the primary studies cited by Dorothy Robinson in fact indicate that in NSW adult cycling INCREASED after the helmet law, and that in Victoria and NSW, child cycling was decreasing BEFORE the helmet laws. Bruce Robinson’s article states that “There is considerable anecdotal and survey information to suggest that bicycle usage has been inhibited by the helmet legislation, but reliable statewide estimates of this are unavailable”. (No references are cited to support the claim of “considerable anecdotal and survey information”.)

    The household surveys in the Marshall study indicate that there was no change in the (overall) amount of cycling after the SA helmet law. The injury data in the Williams study indicates that, consistent with the cyclist surveys, adult cycling INCREASED after the NSW helmet law.

    It is incredible that so much information has been misinterpreted or overlooked by Wardlaw, a “Consultant on Cycling, Health and Safety” (http://cyclehelmets.org/1121.html), and author of the “Cycle safety” chapter in the THSG’s “Health on the Move 2” policy document. It is also incredible that Wardlaw did not feel the need to cite even a shred of evidence to support these (wildly bizarre) claims:

    “The promotion of danger has scared many cyclists out of the traffic, merely to put them at greater risk on pavements and “safe” cycle routes. Experienced cyclists already know that the road system is by far the safest national cycle network that will ever exist.”

    As noted by A/Prof Olivier above, THSG co-chair and JTH editorial board member Watkins has proclaimed that “We still find ourselves having to fight defensive campaigns, such as resisting proposals for compulsory cycle helmets which will do little for cycle safety but will have a serious adverse effect on cycling levels, not least because they feed misconceptions about cycle safety.”

    It seems impossible that anybody who has assessed the (non-Wardlaw and non-Robinson) studies described above could hold such views.

    In a letter to the BMJ, criticising the BMA’s support of bicycle helmets/laws (http://www.ncbi.nlm.nih.gov/pubmed/23881991), Watkins says

    “Apart from this single study in unusual circumstances (high rates of voluntary wearing and the law not enforced) all studies of helmet legislation show that cycling rates fall . . . The tragedy is the consequential deaths from diabetes, heart disease, osteoporosis, and mental illness. The case for cycle helmets is weaker than that for helmets when playing football, and similar to that for helmets when driving. The lack of evidence of population

    Astonishingly, Watkins fails to cite any evidence to support his claims of “consequential deaths from diabetes . . .the case for cycle helmets is weaker than that for playing football . . .”.

    Watkins’ (scientific) publication record is almost as scant as Wardlaw’s, how can it be possible that Watkins has been appointed to a (JTH editorial board) position which (ostensibly) requires the ability to assess the “scientific quality” of submissions to the JTH (http://www.journals.elsevier.com/journal-of-transport-and-health)?

    • Hi Linda,

      I’d like to clarify a few points. I was referring to this article co-authored by Mindell, Wadlaw and Deborah Leslie.

      http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0050606

      However, with regards to this paper, I think their title of a ‘Like-for-Like’ assessment using time-traveled as level of exposure is misleading. This comparison makes no sense for people traveling over fixed distances like commuters. So, for example, if it takes someone 30 minutes to cycle to work and 15 minutes to drive by car, the motorist is “at-risk” over a 15 minute period that doesn’t actually happen when using time traveled for exposure.

      I do think your criticisms of Wardlaw’s BMJ commentary are quite valid. There has been considerable conjecture that helmet laws uniformly lead to less cycling. But, much of the source of material indicates otherwise or the evidence is only partially true.Anti-helmet arguments seem to be sustained through selective citation. Note that Robinson’s work on this topic comes in the form of secondary analyses of other people’s work or commentary.

      For instance, Max Cameron and colleagues 1994 Accident Analysis and Prevention paper state in the last sentence of the abstract “Surveys in Melbourne also indicated a 36% reduction in bicycle use by children during the first year of the law and an estimated increase in adult use of 44%.” The results in Sydney were similar with a 22% increase in counts of adult cyclists (Robinson cites the source material in her 1996 paper, but ignores the adult data).

      Wardlaw takes a naive position that inclusion of minor injuries, like superficial lacerations, from hospital data means helmets only protect against those injuries. I believe this is a criticism echoed about our 2011 AAP paper by the Bicycle Helmet Research Foundation (Wardlaw is an editorial board member). First, it is highly unlikely for someone to be hospitalised for such injuries (as Linda points out) and, secondly, it is more likely such patients are hospitalised for other injuries such as long bone fractures or injuries to the thorax/abdomen regions.

      Helmets clearly do not protect against these injuries and the inclusion of those injuries results in conservative helmet efficacy estimates. For example, suppose there are 100 head injuries prior to a helmet law of which 10 are superficial injuries. Now suppose the “real” effect of the helmet law is to cut head injuries in half. The means we’d see 55 head injuries in the post-law period (i.e., half of 90 plus the 10 superficial injuries for patients hospitalised for other reasons). The estimated effect of the law would be a 45% reduction instead of 50%.

      It is possible that superficial injures get wiped out after helmet legislation. But, as Linda pointed out, these make up a very small proportion of hospitalisations (1/2404=0.0004% from Carr et al.).

      With regards to chronic illness like diabetes and heart disease, I’ve seen no one actually relate bicycle helmets with increased incidence of these diseases. The argument is pure conjecture and I find it troubling that viewpoint is being pushed by members of the JTH editorial board.

  8. Pingback: Something Amiss in Robinson (1996) | Injury Stats

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