Livre d'Or

You may be right, I don't have all the key studies at my fingertips. What convinced me not to bother with helmets was Goldacre & Spiegelhalter's summary. They say case-control studies [...] have shown that people wearing helmets are less likely to have a head injury and cite a Cochrane review which sounded credible to me. That may well be the notorious TRT '89 study you refer to here, assuming 89 is a typo for 99, but that's not a single study, it's a meta-analysis. I was convinced by Goldacre's argument that even if it's true that helmets relatively protect people who have similar head-injuring accidents, if they also lead to helmet wearers having more accidents, their effect may be overall increasing rather than decreasing risk. That seemed to me adequate reason to eschew wearing a helmet, without having to give up the intuitively appealing idea that helmets are somewhat protective.