Remember kids... always wear a helmet. (The almighty bikeradar helmet thread)

There's been another Cochrane Review since the one criticised on cyclehelmets.org. You can find the abstract here:

http://www.cochrane.org/reviews/en/ab005401.html

Although the results of the review support bicycle helmet legislation for reducing head injuries, the evidence is currently insufficient to either support or negate the claims of bicycle helmet opponents that helmet laws may discourage cycling.

I think it would be very interesting to see the references and find out what the overlap is with the previous review, if any. Can someone with Athens or whatever dig it out? (Or send me the pdf of the whole thing, if they're feeling generous...)

Main results
Five studies, all from North America, met the inclusion criteria. For each of the studies, bicycle helmet legislation had been enacted for children only. Adults were used as controls in four of the studies, whilst jurisdictions with no helmet legislation were used as controls in the fifth. Three of the studies reported on changes in head injury rates and three reported on changes in helmet use. There were no included studies reporting change in bicycle use or other adverse consequences of legislation. In two studies, statistically significant decreases in head injuries were reported following the implementation of helmet legislation compared with controls, whilst one reported a non-statistically significant decline. Bicycle helmet use increased statistically significantly post-legislation in all three of the studies reporting on helmet use.

Not being able to see the trials (or even the body of the review) is very frustrating! However, as far as I can tell from this precis, all three of the relevant studies compared head injury rates in children prior to helmet legislation with head injury rates in children following helmet legislation. (The adult control groups ensure that head injury rates in the general population remain consistent throughout the trial period).

If you're of the view that adult helmet use and child helmet use are different issues, then it follows that this study does not contribute to the "adult" helmet debate. Personally I think the authors should have picked this up, and perhaps reflected the distinction in the review title.

However, that's not to say that it undermines any case for helmets. I'm helmet agnostic [never seen any convincing evidence for - then again - never seen a decent trial either, and the idea that they could prevent injury makes obvious intuitive sense]. The problem with these reviews, as they acknowledge, is that they're not meta-analyses because there aren't any properly controlled trials. And the problem with controlled, blinded trials on an issue like this is easily illustrated by a classic BMJ article:

Parachute use to prevent death and major trauma related to gravitational challenge: systematic review of randomised controlled trials