Do Helmets Prevent Head Injuries?

Do Helmets Prevent Head Injuries? « Science-Based Medicine
A cycling enthusiast asked me about helmets. It seems compellingly obvious to me that a head impacting the pavement without a helmet is likely to sustain more damage than a head protected by a helmet. He challenged that, citing a BMJ article by Ben Goldacre that questioned whether the evidence showed that helmets do any good. He said I was making a non-evidence-based assumption and challenged me to actually look at the evidence, so I did.

Goldacre says there is a:

complex contradictory mess of evidence on the impact of bicycle helmets. Like most places where there’s controversy and disagreement, this is a great opportunity to walk through the benefits and shortcomings of different epidemiological techniques, from case control studies to modeling.

He proceeds to give a lesson in epidemiology. He points out that there are a lot of emotion involved, and that epidemiologic studies, because of their inherent imperfections, are probably not capable of resolving the debate.

There are basically two questions:

1. What is the effect of wearing a helmet for the individual?
2. What is the effect of a public policy that promotes or requires helmet use?

He shows why research has difficulty answering both of those questions, and covers some of the possible confounding factors:...