Cycle helmets don't reduce head injury risk as much as it's thought, claims new analysis

At a time when minister for cycling Norman Baker is in the headlines due to his choice not to wear a helmet while cycling, an academic from Norway has poured more fuel on the long-running helmet debate by claiming that they do not reduce the incidence of head injuries by the extent suggested by a meta-analysios of previous studies. Moreover, he says that by considering head, face and neck injuries as a whole, there is "no overall effect" through wearing a helmet.

Dr Rune Elvik, an expert in risk analysis and cost benefit analysis from the Institute of Transport Economics says that wearing a meta-analysis conducted in 2001 that claimed that wearing a helmet reduced the risk of head injury by 60% was flawed as a result of publication bias – in other words, more weight was attached to positive findings from the researchers’ point of view than negative ones – and time-trend bias.

According to Dr Elvik, "When these sources of bias are controlled for, the protective effects attributed to bicycle helmets become smaller than originally estimated."

He adds: "When the analysis is updated by adding four new studies, the protective effects attributed to bicycle helmets are further reduced. According to the new studies, no overall effect of bicycle helmets could be found when injuries to head, face or neck are considered as a whole."

His conclusions, based on an analysis of previous research, have been published in the journal Accident Analysis and Prevention, in an article snappily entitled Publication bias and time-trend bias in meta-analysis of bicycle helmet efficacy: A re-analysis of Attewell, Glase and McFadden, 2001 which, in layman’s terms, points out what he believes to be flaws in that study and provides a reanalysis of its findings.

Dr Elvik employed a variety of techniques in his re-evaluation of the findings, conclusing that “the re-analysis shows smaller safety benefits associated with the use of bicycle helmets than the original study,” according to the article overview, which adds that “the findings of this meta-analysis are not consistent with a recently published Cochrane review,” published by the not-for-profit Cochrane Collaboration.

In New Zealand, where bicycle helmets are compulsory, the findings were reported by the NZ Herald, which adds that Dr Elvik also argues that an analysis of several studies published recently shows there was “no net effect” through sporting a helmet once injuries to the head, face and neck were grouped together, because helmets increase the risk of the latter.

Professor Alistair Woodward, head of the School of Population Health at the University of Auckland and a cyclist who himself wears a helmet, told the NZ Herald: "Cochrane is usually regarded as the gold standard in pooling studies and deriving a conclusion.
"It's reasonably clear to my mind that helmets do protect people's heads and on balance they do more good than harm," he continued.

However, he agreed that helmets were not intended to guard against neck injuries.
"Whether they cause the neck to bend more than otherwise, I suppose it's possible. If there is an effect [on neck injuries], it's much smaller than the protective effect from head injuries."

Professor Woodward said he was in accord with the conclusion that modern, lightweight helmets with a soft shell protected the head less than older ones with a hard shell.

"The first helmets were [made for] rock-climbing,” he explained. “Only later, people realised the energy-absorbing material inside the shell is probably what's more important ... and the surface of the helmet has become more vented and less rigid," Professor Woodward added.