Originally Posted by
chephy
This is about as faulty a study as any that has ever been published anywhere. Interestingly, the helmet advocates always pick this study - just about the shoddiest helmet study around - to support their view point. Mainly because they like the look of the stats - they align nicely with their prejudices.
WRONG.
That study is NOT faulty.
The pathetic attempt from our friends at the "Bicycle Helmet Research Foundation"? I already gutted that like the dead fish it is
here. I'll repeat the gutting for your perusal:
And now to deconstruct the "refutations" of the studies that concluded bike helmets conclusively help prevent head injuries. First, this one, from the Bicycle Helmet Research Foundation (whoever they are...)
http://www.cyclehelmets.org/1068.html:
This paper (TRT89) is by far the most frequently cited research paper in support of the promotion of cycle helmets. It is referred to by most other papers on helmets. In fact, many other papers, and nearly all helmet promotion policies, rely fundamentally upon the validity of its conclusions.
The claims that helmets reduce head injuries by 85% and brain injuries by 88% come only from this source, yet are quoted widely as fact. For example, a policy statement on bicycle helmets by the American Academy of Pediatrics in 2001 states: “The bicycle helmet is a very effective device that can prevent the occurrence of up to 88% of serious brain injuries.” [1]
The prospect of achieving such massive reductions in injuries to cyclists lies at the root of helmet promotion and helmet laws around the world. Those who have taken the trouble to analyse the paper in detail, however, have found it to be seriously flawed and its conclusions untenable. Moreover, by making different - but no less valid - assumptions, the conclusions change radically.
Well, let's see. Will the conclusions change radically?
Although the authors call odds ratios “percentage reductions in risk”, it is more informative to use risk ratios (RR) = %HIH / %HIN where %HIH and %HIN are the percentages of helmeted and non-helmeted cyclists with head injuries. TRT89 reported data for cyclists attending the emergency department for non-head injuries. For this group, which can be considered as an alternative control, the risk ratio was 0.36, suggesting that helmets prevented 64% of head injuries.
McDermott et al.[3] obtained more information and reported numbers of head injuries excluding forehead lacerations in the TRT89 study. The risk ratio excluding forehead lacerations was 0.39, a small reduction in the estimated benefit of helmets.
McDermott’s data on hospital admissions also illustrates the folly of labelling odds ratios as risk ratios. 28.6% of adult cyclists who wore helmets still had head injuries. If helmets prevented 85% of head injuries, an impossible 191% of non-helmeted cyclists would have head injuries. The actual figure (38%) was higher than for helmet wearers, but the difference due to helmet wearing was not statistically significant. [3]
FAIL, right there.
Book cooking in progress.
The "28.6% of cyclists who wore helmets" but "still had head injuries" are from the SUBSET of cyclists who were admitted to the hospital. In other words, the criteria for hospital admission is independent of whether or not the cyclist was wearing a helmet.
The "refutation" of the study I linked is FATALLY flawed. One wonders if it's deliberately misleading. There's no real need to continue, now is there?
But let's continue anyway...
A study in Tucson, Arizona, of bike/motor vehicle collisions found that helmet wearers had less severe non-head injuries. The authors concluded: "This implies that nonusers of helmets tend to be in higher impact crashes than helmet users. It is possible that at least some of the 'protection' afforded helmet wearers in previous studies may be explained by safer riding habits rather than solely a direct effect of the helmets themselves" [5].
Woo, that's a strong statement. Not.
The authors reported only 3 age categories: <15, 15-24 and 25+. However, a subsequent analysis of a subset of the same data [6] showed that 83% of children aged 0-4 suffered head injury, compared to 42% of 5-9 year olds and 23% of 10-14 year olds. Such large differences suggest that age adjustment in the original study may have been inadequate and hence the conclusions invalid.
Some more hemming and hawing...
Conclusion
The study compares groups of cyclists who chose to wear helmets with those who did not.
Well, duh.
That's the entire point of the study.
Many variables, such as the reasons for wearing a helmet and attitudes to risk, were not controlled for by the researchers and may have influenced the results.
Wow.
When we get to the conclusion, we find we waded through lots of noise and fury and got NOTHING. "may have influenced the results"?!!? Where's the "radical change" to the conclusions we were promised?
Did those "conclusions change radically", as promised above?
No. Not at all.
The "refutation" goes from that promise to "may have influenced the results".
Good God, that's lame.