Rapid Responses to:
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Rapid Responses: Rapid Responses published:
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![[Read Rapid Response]](/icons/misc/sectionDOWN.gif)
Absolute risk reduction is the figure that counts
- Edwin P Kirk (4 February 2005)
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At risk of confusion or confusion of risk
- Matthew P Doogue (7 February 2005)
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...and water is wet and blood is red.
- Peter w Ward (8 February 2005)
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Re: Absolute risk reduction is the figure that counts
- Brent E. Hagel (10 February 2005)
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Re: At risk of confusion or confusion of risk
- Brent E. Hagel (10 February 2005)
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do helmets prevent head injuries or people's behaviour?
- dan keown (10 February 2005)
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Cochrane review of bicycle helmets: an unsound guide
- William J. CURNOW (23 February 2005)
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Ski helmets do not protect faces
- Toby KA Baring (16 March 2005)
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Re: Ski helmets do not protect faces
- Brent E. Hagel (22 March 2005)
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Effectivness of helmets
- Matthew Robert Gammons (19 January 2006)
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Edwin P Kirk, Staff specialist Dept of Medical Genetics, Sydney Children's Hospital, Sydney, NSW, Australia
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Hagel et al may be overstating their case a bit. Their discussion states: "Wearing a helmet while skiing or snowboarding may reduce the risk of head injury by 29% to 56%—that is, for every 10 people who wear helmets, three to six may avoid head injuries". Indeed they may, if the incidence of head injuries among non-helmet wearing skiers and snowboarders is 100%. I suspect the real figure is rather lower than that! The absolute reduction in risk is the figure that would influence my decision about wearing a helmet. My guess is that this number will turn out to be small - 29 to 56% of not much. It shouldn't be too hard to reach an estimate of this in terms of injuries per days spent on the snow - the 19 resorts undoubtedly have figures for how many people used their lifts during the season in question. Competing interests: Non-helmet wearing skier |
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Matthew P Doogue, Clinical Pharmacology Registrar Christchurch Hospital
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The risk reduction provided by helmets is much greater for cyclists than for skiers. Is this entirely due to mechanistic factors, or are their psychological factors? Protective equipment usually reduces actual risk, however protective equipment can also reduce perceived risk. Behaviour is affected by perceived risk. Frequently safety measures provide less than predicted as we find new ways to achieve our goals. Some safe activities have a high perceived risk (e.g. bungy jumping) and some dangerous activities have a low perceived risk (e.g. driving around your own neighbourhood) Skiing and snowboarding injuries are affected by behaviour. Is the protection of helmets offset by an increase in risky behaviour by helmet wearers? Extending the study to non head and neck injuries would provide valuable data. Will I start wearing a helmet skiing, as I do cycling? No. Will I expect my children to? You bet. Differing perceived risk or parental predjudice? Competing interests: Ex ski patroller now a Physician, a knee pad wearing telemarker and a helmet wearing cyclist. |
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Peter w Ward, GP Gateshead
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So we have established that wearing a helmet while skiing helps to stop you damaging your head. Can we now look forward to other exciting revelations in the coming weeks in the BMJ, such as that coats (to a statistically significant degree)keep you warm and that umbrellas keep the rain off your head? Competing interests: Non helmet wearing cyclist and nordic skier |
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Brent E. Hagel, Assistant Professor Alberta Centre for Injury Control & Research, Dept. of Public Health Sciences, University of Alberta
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I would like to thank Dr. Kirk for his interesting comments. I do, however, disagree with some of his assertions. First, in the preventive fraction calculation, no assumption is invoked about the incidence of head injury among those not using helmets. The preventive fraction is simply based on a relative difference in the risk of head injury between helmet users and non-users. We might alternatively say that between 29% and 56% of the excess head injury risk among those not using a helmet is due to their failure to use a helmet. Again, there are no assumptions about the incidence of head injury among those not using helmets. Second, although I agree that it would be interesting to have information on measures of absolute risk (risk differences), it is not simply a matter of counting lift tickets at the 19 resorts. We would need information on the joint distribution of lift tickets by, at the very least, age, sex, activity, and helmet use – all factors that affect the risk of injury. This information is not readily available. In any case, these arguments are somewhat specious - our data show that helmets protect the head. Perhaps Dr. Kirk will now become a helmet wearing skier? Competing interests: None declared |
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Brent E. Hagel, Assistant Professor Alberta Centre for Injury Control & Research, Dept. of Public Health Sciences, University of Alberta
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I would like to thank Dr. Doogue for his interesting comments. The risk compensation or risk homeostasis argument he outlines is often used against safety measures with little supporting evidence.(1-2) When we did “extend the study to non head and neck injuries,” we found no evidence that helmet use influenced injury severity or crash circumstances (3); a finding inconsistent with risk compensation theory. 1. Thompson DC, Thompson RS, Rivara FP. Risk compensation theory should be subject to systematic reviews of the scientific evidence. Injury Prevention 2001;7(2):86-88 2. Robertson LS, Pless IB. For and Against: Does risk homoeostasis theory have implications for road safety. Against. British Medical Journal 2002;324(7346):1149-52 3. Hagel BE, Pless IB, Goulet C, Platt R, Robitaille Y. The effect of helmet use on injury severity and crash circumstances in skiers and snowboarders. Accident Analysis & Prevention 2005;37(1):103-108. Competing interests: None declared |
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dan keown, staff grade ED CT20 5EA
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We've been through this before with cycle helmets. The early studies showed dramatic improvements with helmets in the ED (Thompson et al) only to find that when this was examined later in the whole population there was no change despite massive helmet use (Scuffham). As doctors we should be asking ourselves why this is the case. The explanation may lie in the complexity of human nature. We are not comparing like with like. People who voluntarily choose to wear helmets are different to people who choose NOT to wear one. That difference IS important. In fact it may just be that difference that we are measuring. They may take more risks and hence have more severe accidents and be less likely to report minor ones. It would then look like the helmets prevented head injuries when in fact it was merely the more risk averse personality type that was protective. Competing interests: non helmet wearing cyclist/ skier/snowboarder/pedestrain and motor vehicle user |
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William J. CURNOW, Independent researcher Canberra, Australia
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The authors note that helmets are not yet widely recommended for skiers and snowboarders because of paucity of information on their effectiveness. Then, citing the Cochrane systematic review "Helmets for preventing head and facial injuries in bicyclists" (Thompson et al., 2000) for guidance, they conclude that helmet use would seem to be reasonable due to compelling evidence that helmets are effective in preventing head, brain and facial injuries in bicyclists. The review by Thompson et al. is not a reliable guide to the efficacy of bicycle helmets because Cochrane procedures did not require it to be subject to peer review in the same way as articles published in refereed journals. Similarly, the several comments critical of the conclusions of Thompson et al. that have been submitted to the Cochrane library have been referred only to the authors, who rebutted all criticisms and refused to modify the review. In my view, they did not refute the criticisms, in particular my own which concludes that the review provides no evidence that the soft helmets predominant since it was published protect the brain at all. Its claim to establish scientific evidence that all standard types of bicycle helmet protect against brain injury is therefore not supported. In an attempt to ensure that my criticisms of the Cochrane review of bicycle helmets get due consideration, I submitted to the journal Accident Analysis & Prevention an article entitled "The Cochrane Collaboration and bicycle helmets". Recently it was accepted for publication. It concludes as follows: (a) The critical efficacy of helmets is against fatal and disabling injury to the brain. (b) The review's conclusion that its five included studies establish scientific evidence that standard bicycle helmets of all types protect against injury to the brain is not supportable because none of the studies possesses the requisite scientific rigour. (c) Due to the decline in use of hard-shell helmets, past findings of their efficacy are not applicable to most helmets now used. (d) The review is not a reliable guide to interventions and is not suitable for the Cochrane library. Contrary to Hagel et al. there is no compelling evidence that bicycle helmets of current design prevent brain injuries. W.J. Curnow Competing interests: None declared |
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Toby KA Baring, SHO plastics St Thomas' Hospital, Lambeth Palace Road, London SE1 7EH
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The authors have made these decisions in terms of the data collection
for this studies which need some clarification:
This goes on to beg the question:
Surely it would be reasonable to exclude injuries to the face from this study and that should remove the majority of injuries where googles/sunglasses were damaged. Competing interests: None declared |
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Brent E. Hagel, Assistant Professor Alberta Centre for Injury Control & Research, Dept. of Public Health Sciences, University of Alberta
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I would like to thank Dr. Baring for these comments. To clarify, we did not exclude facial injuries from the analysis only if they had another accompanying head injury. This is consistent with including as cases, those individuals who had head injuries as well as arm or leg injuries, for example. Regardless, it is not clear, as evidenced by the protection afforded the face by bike helmets,(1) that ski and snowboard helmets would not protect this region. Regarding comment 2, we did not exclude those who damaged their goggles/sunglasses. They were in fact included in the analysis. However, we did not code these individuals as having equipment damage or as having other, non-helmet, protective equipment. Our main intent was to obtain a proxy measure of crash severity and we did not feel that damage to goggles or sunglasses represented the same kind of crash circumstances that would produce damage to skis, bindings or poles, for example. 1. Thompson et al. Effectiveness of bicycle safety helmets in preventing serious facial injury. JAMA 276(24): 1974-1975. Competing interests: None declared |
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Matthew Robert Gammons, Sports Physician Killington Medical Clinic, Killington, VT 05751
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I read with great interest your recent article entitled- Effectiveness of helmets in skiers and snowboarders: case-control and case crossover study BMJ 2005; 330: 281- My partner and I have a 20+ year history of running an on mountain winter sports clinic. During this time we have made several observations that I believe detract from the authors ability to draw their conclusions. 1.The initial diagnosis made by ski patrollers is often not accurate and that not all injuries taken off the mountain by ambulance are severe and many severe injuries do not get ambulance transport. This information comes from follow up of ambulance runs we have done over the years and patients seen in our clinic. 2. Patrolers both grossly overestimate and underestimate injury severity. 3. Patrollers are less likely to assume severe head injury in those wearing helmets. This potentially leads to the under diagnosis of severity of head injuries in helmeted skiers and snowboarders based on this bias. 4. Most patients we see have a difficult time describing the events and conditions surrounding their injury. Their story often changes significantly from the time they are evaluated on the mountain and when they are evaluated in our clinic. This information is very likely to lose additional accuracy as time passes and I am concerned that your follow up information biased. Did the authors have ER reports or follow- up physician reports in addition to patient follow-up? If not I believe it would be difficult to accurately determine the relative severity of injuries. I applaud the authors’ attempt to quantify the effect helmets have on skier and snowboarder safety but I fear they have significantly overestimated the effect. Sincerely,
Competing interests: None declared |
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