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

stats/maths is doing my head in

That's why people like simple stories. The one which gets traction is "a helmet saved my life". While unlikely to be true every time it is claimed, it is also unlikely that it is never true. The real story is complicated, full of caveats, bound up with statistics and probability which are the two kinds of maths most people are really bad at; "If making helmets compulsory invoked full compliance among the subset of cyclists not already voluntarily using helmets, and if they made no other changes to their behaviour which confounded this intervention, and if cycle helmets were actually highly effective at reducing the severity of head injuries experienced in real world bicycle crashes, then we would still have to study a large population for a long time to be able to measure with confidence whether our intervention had made any difference" is a bit long and complicated for somebody who has just smacked their head on the tarmac to tweet.