@reddan, that’s basically Steven’s objection, too, but at least one of the studies from the Cochrane review explicitly considers it, McDermott 1993: ‘Protective effect of helmets does not appear to be due to cautious riding behavior by helmeted cyclists. This is based on observations that “collision of cyclists” head, face, or helmet with motor vehicles occurred slightly more often to helmeted casualities than to unhelmeted casualties (17.6% versus 14.5%).’
It’s also interesting to note that one of the claims people sometimes make about helmets is that they don’t really help because cyclists with helmets just engage in more risky behavior (which McDermott sort of supports). Now we’re saying that cyclists with helmets are more cautious. Shows how important it is to actually measure.
Also, BTW, these multiple studies show a large protective effect against head injury — it’s not slight. Of course, you’re not protected against anything else — but the brain is the one organ in your body where even a small injury can seriously mess up your life.
Yeah, I saw that, even wrote to the CPSC to ask about what they were doing to update helmet standards to handle concussions better. But as a result of this discussion, I now think that helmets are so good (and serious bicycle accidents so rare) that it’s probably a waste of time. If you’re wearing a helmet, you have a very good chance of avoiding brain injury, including concussion, if you’re in an accident. Maybe a better designed helmet would make that chance even better, but it’s probably not worth it.