Sir,

This article brings into prospective a dangerous and habitual practice of leaving infants and children unattended in vehicles and its serious ill effects on health most notably being death. Although the article describes scenario in a developed western setup such incidents are increasingly becoming common in developing Asian countries like India and require immediate attention.

The study addresses an important and often ignored issue of occurrence of hyperthermia in children left unattended in vehicles. There is a strong need that print and social media should bring such shocking occurrences into public domain more piercingly so that people specially parents together with caretakers would become aware of such problems leading to them being more careful and attentive. The community as a whole should bring about basic necessary changes in attitude and perception of individuals to prevent such dreadful events.

We agree with the authors that policy makers and law makers need to take a serious and stringent look into such issues so that timely interventions and strict regulations can be put into place. The community and government should work interactively towards developing guidelines, safety norms and mostly create awareness amongst ignorant parents.

Lastly we would like to state that in a country like India with warm winters and ambient temperatures being high normal in most part of country throughout the year along with little awareness about such a catastrophic phenomenon, a study in Indian context is urgently required.

Conflict of Interest:

None declared

The case-crossover method in its familiar application is to look for factors that recur when cases occur, for individuals crossing exposure to them as examined over a time interval. This study [1-3] applies the method in a different way, the exposures being examined over a spatial route, with neither the identified factors nor the various routes being independent of the highly constrained urban geographies of the settings. Thus in addition to all the familiar vulnerabilities of the case-crossover method [4-9]-- some of which require translation to the new context-- this application brings new problems of its own. It is not possible to note even most of just the major ones in this correspondence, and further criticism may be found elsewhere [10-12]. I thank the authors for kindly providing extra information as necessary for the following analyses.

1. Control site selection bias.

The authors find control sites by random selection along the route the injured rider took. Contrary to [2], such comparisons only make sense if the control locations match the case locations by intersection status, which often they do not. To make them match, in [3] the authors randomly adjust selections forward or back until they do. This was necessary for about 70% of the cases at intersections, and 30% at non-intersections.

In these instances, selection of control intersections is dependent on their spatial distribution along the route, but indifferent to their widths. This biases their selection in favour of smaller intersections associated to longer non-intersection segments. Likewise, the selection of non-intersection control sites is disproportionately biased in favour of whatever are adjacent larger intersections.

For example, over a route whose length is 30% intersections, 70% non- intersections, beginning at 0 and having terminated at 1, with intersections between 0 and 0.05, 0.5 and 0.6, and 0.85 to 1, the probabilities of choosing the three intersections as control sites should occur in ratios of 1:2:3. But by the authors' adjustment method, in those instances where adjustment is needed, they are respectively 0.5 x 0.45/0.7, [(0.5 x 0.45)+ (0.5 x 0.25)]/0.7, 0.5 x 0.25/0.7, thus occurring in ratios of approximately 1:1.56:0.56. Maclure [4] has discussed the potentially large biases in relative risk estimates that can result from not taking intersection widths into account.

There is already selection bias before this stage. For example, consider a route with no intersections, having a bicycle-specific facility in the first and last thirds only. Suppose injury events occur at random along this route. They should therefore occur in facilities and non-facilities in proportions of 2:1, and likewise so should the selection of control sites. But under the authors' method of selection, the probability of the control being in a facility is [2+ln(4/3)]/3, so that instead the proportions are about 3.21:1.

Such problems have been discussed extensively in the meteorological literature on case-crossover studies [7-9], and by Maclure in the epidemiological literature [4].

There is still another potential randomisation failure at this level of selection to consider. The standard deviation of the uniform distribution on [0, 1] is almost one-third (1/[2*SQRT(3)]). For individual runs of only 801 in length (for non-intersections), or 272 (for intersections), this can easily result in quintiles being out of balance by plus or minus 10 to 25%, which can again skew the estimates. (Thus the reader wishing to closely check by simulation the probability calculations given above should use a much larger n, such as on the order of 10^5.)

2. Anomalous or internally inconsistent results.

(1) The authors note that contrary to previous studies, they found surplus injuries at intersections with the greatest bicycle traffic. They suggest their finding may not be generalisable. But they do not explain why their method should have led to a non-generalisable result.

The authors' method does not track the effect of an independent variable-- in this case, cyclist traffic-- as it varies at a fixed location. Instead it ranges over entirely different locations, which coincidentally may have different values of the independent variable. Yet cyclists do not choose their routes at random, and many routes may share intersections and links.

In most cities there are inherently hazardous locations that attract bicycle traffic because they are in some way inevitable, such as for being the only way to access a bridge. Thus even if control site selection within routes had been correctly randomised, this would not balance the bias across routes.

Nor is bicycle infrastructure installed at random. Instead, the locations for it are typically chosen either to take advantage of already safe circumstances, or to address special hazards, via multiple special measures. Thus another set of anomalous results, this time put forth as addressing the cycle track controversy:

(2) The authors find bicycle-only paths in parks to be 17.6 times as dangerous as bicycle-only paths in streets. They find multi-use paths in parks to be 22.8 times as dangerous as bicycle-only paths in streets.

The fundamental (not the only) hazard of cycle tracks is that they force cyclists to be in the path of turning and crossing vehicles at junctions. The protection they can offer is only between junctions, where the absolute risks are lower, while they force cyclists into danger at junctions, where the absolute risks are higher [13]. Attempts to mitigate the hazards at junctions generate inconvenience and frustration for all users, such that their benefits may not be durable, as was the case for the Burrard Bridge in Vancouver subsequent to the authors' short study period [14].

The authors' work estimates only relative risks of cycle tracks, and only between intersections. By missing both absolute risks and the action at intersections, it does not do anything to address the cycle track controversy, and it is wrong to use its results to promote cycle tracks.

The only novel cycle track result from this study is the anomalously large relative benefit it ascribes to cycle tracks between intersections. This limited result suffers from the following weaknesses:

(i) As found by the authors and others, the majority of cyclist injury events, including hospitalisations, result from bicycle-only crashes [2, 15, 16]. As noted by others, if cycle tracks work by protecting cyclists from motor vehicles, how can they reduce injuries by 95%, if the majority of such injuries have nothing to do with motor vehicles?

(ii) If cycle tracks work by protecting cyclists, then the authors' results that introduced this section indicate cyclists need protection most of all not from motor vehicles, but from pedestrians and squirrels.

References

2. Teschke K, Harris MA, Reynolds CCO, Winters M, Babul S, Chipman M, et al. Route Infrastructure and the risk of injuries to bicyclists: a case-crossover study. Am J Pub Health 2012;Oct 18:e1-e8. doi:10.2105/AJPH.2012.300762.

3. Harris MA, Reynolds CCO, Winters M, Cripton PA, Shen H, Chipman ML, et al. Comparing the effects of infrastructure on bicycling injury at intersections and non-intersections using a casecrossover design. Inj Prev 2013;0:18. doi:10.1136/injuryprev-2012-040561.

4. Maclure M, Mittleman MA. Should we use a case-crossover design? Ann Rev Public Health 2000;21:193221.

5. Redelmeier DA, Tibshirani RJ. Interpretation and bias in case-crossover studies. J Clin Epidemiol 1997;50;1281-1287.

6. Sorock GS, Lombardi DA, Gabel CL, Smith GS, Mittleman MA. Case-crossover studies of occupational trauma: methodological caveats. Inj Prev 2001;7(Suppl I):i3842.

7. Lee J-T, Kim H, Schwartz J. Bidirectional casecrossover studies of air pollution: bias from skewed and incomplete waves. Env Health Perspectives 2000;108:1107-1111.

8. Bateson TF, Schwartz J. Selection bias and confounding in case-crossover analyses of environmental time-series data. Epidemiology 2001;12:654-661.

9. Lumley T, Levy D. Bias in the case-crossover design: implications for studies of air pollution. NRCSE Technical Report Series NRCSE-TRS No. 031, 1999.

10. Kary M. Vulnerabilities of the case-crossover method as applied, and unsuitability of the epidemiological approach, to transportation injuries and traffic engineering problems-- Part I. http://john-s-allen.com/blog/?page_id=5705 (accessed Dec 2013).

11. Kary M. Vulnerabilities of the case-crossover method as applied, and unsuitability of the epidemiological approach, to transportation injuries and traffic engineering problems-- Part II. http://john-s-allen.com/blog/?page_id=5702 (accessed Dec 2013).

12. Allen JS. Safe bicycle routes: engineering versus epidemiology. 2013. http://john-s-allen.com/blog/?p=5522 (accessed Dec 2013).

13. Bicycle infrastructure and safety. Transport Canada, Urban Environmental Programs: Case Studies in Sustainable Transportation, Issue Paper 90. March 2012. http://publications.gc.ca/collections/collection_2012/tc/T41-1-90-eng.pdf (accessed Dec 2013).

14. City of Vancouver. Downtown Separated Bicycle Lanes Status Report, Spring 2012. June 5 2012. http://bikeroute.files.wordpress.com/2012/06/downtown_lanes_report.pdf (accessed Dec 2013).

15. Aultman-Hall L, Kaltenecker MG. Toronto bicycle commuter safety rates. Accident Analysis & Prevention 1999;31(6):675-86.

16. Boufous S, de Rome L, Senserrick T, Ivers RQ. Single- versus multi- vehicle bicycle road crashes in Victoria, Australia. Inj Prev doi: 10.1136/injuryprev-2012-040630.

17. Chipman ML, MacGregor CG, Smiley AM, Lee-Gosselin M. Time vs. distance as measures of exposure in driving surveys. Accident Analysis & Prevention 1992;24:679-684.

Conflict of Interest:

None declared

I would like to add to the Editor's argument [1] by emphasising the uniqueness, and the potential value, of the East York ridership dataset.

Over the past 23 years, laws prohibiting children (or everyone) from riding bicycles, unless they wear helmets, have been enacted in hundreds of American municipalities, the large majority of American states, seven out of ten Canadian provinces, all of Australia and New Zealand, and numerous other jurisdictions around the world. In how many of these jurisdictions was child ridership objectively documented, to see whether the helmet requirement had any adverse effect upon it?

Irresponsibly, in almost none. So far, only in Melbourne (Victoria law, implemented in 1990) and New South Wales (law implemented in 1991); in Calgary, Edmonton, and surrounding communities (Alberta law, implemented in 2002); and in East York (Ontario law, implemented in 1995). The Australian data were published in a scientific journal in 1996 [2], while the Alberta data, collected in 2000 and 2006, still languish in a PhD thesis [3]-- perhaps because they are so unfavourable to helmet legislation. (There are other examples of relevant ridership data that have been collected, but not disseminated, such as for British Columbia [4], and Duval County, Florida [5, 6, 7].) Only in East York were the surveys carried out annually or biennially over a relatively long time span, 1990 to 2001.

The East York dataset should be a particularly useful complement to the others for additional reasons. For one, unlike in Australia, and several other major and minor jurisdictions, there has never been any police enforcement of the law. From the beginning, police forces said they would not, or could not, enforce it [8]. For another, bicycle helmet laws do not spring up overnight: they are preceded by campaigns to increase the perceived dangerousness of bicycle riding. In both Australia and Ontario as elsewhere, these campaigns long preceded the actual introduction of the legislation [9, 10, 11]. Yet in Australia, the single early survey was done after the campaigns were already well underway; and not done during the same season of the year as the later ones-- November to January for 1987/88, but May and June of 1990, 1991, and 1992 [10]. Only in East York was there a survey done (1990) before much, though by no means all [9, 11], of the early campaigning; and only in East York was there also rough seasonal consistency, the observation periods being August and September of 1990, June through October of 1991 and 1992, and what has been described as either May to September [12] or April to October [13, 14, 15] of 1993-2001.

And therein lies a rub, or at least a first hint of one. Unlike for Australia and Alberta, the East York surveys have been described neither consistently nor completely, and this not just for the dates but crucially, for the sampling strategies, efforts, and site selections as well [16]. Worse, the actual numbers of cyclists counted have been reported with not just small discrepancies, but huge and incomprehensible ones [Table 1]. Even the notice of correction [17] appended to the original study is itself in need of a correction notice, for-- as we can now determine, the actual corrections at last having been published-- every statement in it is false. As summarised by the Editor [1], "the inconsistency without explanation diminishes the credibility of the results and diverts attention from the central research question."

Table 1.

Table 1, continued:

What then are we to make of the East York data? With such inconsistencies, and no help from the authors forthcoming, the natural conclusion is: little or nothing of scientific value.

I have come to believe that, with some clarification, this conclusion-- and the shameful waste it would imply, of over a decade of research effort on an unrepeatable historical circumstance-- is not inevitable, and this was one of the motivations for my complaint to Injury Prevention. Regardless of any data destruction, the authors should be able to tell the research community whether there was a survey in 1989, or not; and if not, on what basis they were able to say that the helmet use rate in that year was 0% [11]. The authors should be able to tell us whether the sites sampled, or their number, were the same for every year from 1990 to 2001 [15]; or not the same [14]. The authors should be able to tell us whether, as seems the only logistical possibility, the 1990 survey was a minimal one, and therefore had all sites or areas sampled to the same extent. They should be able to tell us if, as seems implied by the statistical goals (to roughly double the 1990 sample size) and the time budget (again roughly double), the 1991 survey also had double the number of survey hours, and whether these were again uniformly distributed amongst the sites or areas; or if not, then according to what strategy. The authors should be able to tell us what the situation was for 1992, and then again with regard to the overall sampling strategy for 1993-2001. And the authors should be able to tell us by what method they aggregated the site-level cyclist counts and numbers of survey hours into overall rates, something they have yet to clearly explain.

I think these are the minimal explanations that the authors owe the research community, whose members have endeavoured to understand, or wrongly used [23], their work; the bicycling community, whose members had to defend their way of life against the premise of it [24, 25]; and the Canadian taxpayer, who paid for it.

References

1. Johnston BD. Living in the grey area: a case for data sharing in observational epidemiology. Injury Prevention 2012;0:1–2. doi:10.1136/injuryprev-2012-040671.

2. Robinson DL. Head injuries and bicycle helmet laws. Accid Anal Prev 1996;28:463-475.

3. Karkhaneh M. Bicycle helmet use and bicyclists head injuries before and after helmet legislation in Alberta Canada. PhD thesis, University of Alberta, 2011.

4. Foss RD, Beirness DJ. Bicycle helmet use in British Columbia: effects of the helmet use law. Pre-and post-law bicycle helmet use in British Columbia. April 2000. University of North Carolina Highway Safety Research Center; Traffic Injury Research Foundation. http://www.hsrc.unc.edu/safety_info/bicycle/helmet_use_bc.pdf (accessed Feb 24 2009).

5. Bicycle helmet use laws: lessons learned from selected sites. National Highway Transportation Safety Authority. http://www.nhtsa.gov/people/injury/pedbimot/bike/bikehelmetuselawsweb/pages/7ProfileBJacksonvill.htm (accessed Nov 18 2012).

6. Conserve by Bicycle Phase 1 Study: Report. Florida Department of Transportation. http://www.dot.state.fl.us/safety/ped_bike/brochures/pdf/CBBphase1%20Report062907.pdf(accessed Nov 18 2012).

7. Florida Traffic and Bicycle Safety Education Program. www.saferoutesinfo.org/sites/default/files/page/Pieratte.pdf (accessed Nov 18 2012).

8. Wright L, MacKinnon DJ. Province eyes tougher law on helmets . The Toronto Star (metro edition). 1996;Oct 17:A2.

9. Legislative Assembly of Ontario, committee transcripts: Standing Committee on Resources Development, November 20, 1991 - Bill 124, Highway Traffic Amendment Act, 1991. <http://www.ontla.on.ca/web/committee-proceedings/committee_transcripts_details.do?locale=en&Date=1991-11-20&ParlCommID=105&BillID=&Business=Bill+124%2C+Highway+Traffic+Amendment+Act%2C+1991&DocumentID=17013> (accessed Nov 18 2012).

10. Finch CF, Heiman L, Neiger D. Bicycle use and helmet wearing rates in Melbourne, 1987 to 1992: the influence of the helmet wearing law. Monash University Accident Research Centre 1993;Report No. 45. http://monash.edu.au/muarc/reports/muarc093.html (accessed Jul 25 2009).

11. Wesson D, Spence L, Hu X, et al. Trends in bicycling-related head injuries in children after implementation of a community-based bike helmet campaign. J Ped Surg 2000;35:688-689.

12. Macpherson AK. An Evaluation of the Effectiveness of Bicycle Helmet Legislation. PhD Thesis, Institute of Medical Sciences, University of Toronto 2003.

13. Parkin PC, Khambalia A, Kmet L, Macarthur C. Influence of socioeconomic status on the effectiveness of bicycle helmet legislation for children: a prospective observational study. Pediatrics 2003;112:e192-e196.

14. Khambalia A, MacArthur C, Parkin PC. Peer and adult companion helmet use is associated with bicycle helmet use by children. Pediatrics 2005;116:939-942.

15. Macpherson AK, Macarthur C, To TM, Chipman ML, Wright JG, Parkin PC. Economic disparity in bicycle helmet use by children six years after the introduction of legislation. Inj Prev 2006;12:231-235.

16. Kary M. Compendium of errors and omissions in Canadian research group's bicycle helmet publications. http://www.cyclehelmets.org/papers/c2031.pdf (accessed Dec 1 2011).

17. Update to Macpherson et al. 7 (3): 228. Correction. Inj Prev 2006;12:432. http://injuryprevention.bmj.com/content/12/6/432.full (accessed Nov 18 2012).

18. Parkin PC, Spence LJ, Hu X, Kranz KE, Shortt LG, Wesson DE. Evaluation of a promotional strategy to increase bicycle helmet use by children. Pediatrics 1993;91:772-777.

19. Parkin PC, Hu X, Spence LJ, Kranz KE, Shortt LG, Wesson DE. Evaluation of a subsidy program to increase bicycle helmet use by children of low-income families. Pediatrics 1995;96:283-287.

20. Macpherson AK, Parkin PC, To TM. Mandatory helmet legislation and children’s exposure to cycling. Inj Prev 2001;7:228–230.

21. Robinson DL. Helmet laws and cycle use. Inj Prev 2003;9:380–383.

22. Macpherson AK. An Evaluation of the Effectiveness of Bicycle Helmet Legislation. http://www.neurosurgery.pitt.edu/circl/webinars/archive/2005/documents/macpherson_101105.pdf (accessed Dec 15 2008).

23. Legislation for the compulsory wearing of cycle helmets. British Medical Association Board of Science and Education, November 2004. http://www.helmets.org/bmareport.htm (accessed Nov 18 2012).

24. Testimonies of Neil Farrow and of the Windsor Bicycling Committee. Legislative Assembly of Ontario, committee transcripts: Standing Committee on Resources Development, December 02, 1991 - Bill 124, Highway Traffic Amendment Act, 1991. <http://www.ontla.on.ca/web/committee-proceedings/committee_transcripts_details.do?locale=en&Date=1991-12-02&ParlCommID=105&BillID=&Business=Bill+124%2C+Highway+Traffic+Amendment+Act%2C+1991&DocumentID=16994> (accessed Nov 18 2012).

25. Testimony of Marcia Ryan. Legislative Assembly of Ontario, committee transcripts: Standing Committee on Resources Development, November 25, 1991 - Bill 124, Highway Traffic Amendment Act, 1991. <http://www.ontla.on.ca/web/committee-proceedings/committee_transcripts_details.do?locale=en&Date=1991-11-25&ParlCommID=105&BillID=&Business=Bill+124%2C+Highway+Traffic+Amendment+Act%2C+1991&DocumentID=16980#P181_55605> (accessed Nov 18 2012).

Conflict of Interest:

None declared