Cool with that. As I said at the beginning, I was reticent to get involved in the argument, it's too much like a religion for me (and I care about as much, I commute and 'train' with a helmet on, I leisure ride quite happily without one and I make the choice purely for myself either way). It just struck me that the talk of there being insufficient data about helmets doing good stands a good chance of being because people don't report the injuries they didn't get. Of course that opens up the can of worms of 'would the injury be there at all if...' and without a serious study involving parallel dimensions it all gets a bit tough to actually prove. And we're back to Faith.
You're right about the religion bit and I was thinking about throwing it in but changed my mind, you've changed it back
With God it's called Pascal's Wager, you believe in God just in case, you lose very little if you're wrong but gain plenty if you're right.
The issue with this though is the "just in case bit". As you've been saying there is surely a point where a helmet is effective against some types of injury, I often debate this with myself and wonder if I would be better off with one "just in case". What you have to weigh it up against are the other everyday activities which could result in some sort of head injury. My friend that fell off on the corner is a motor mechanic, he spends his days with his head under bonnets and standing under cars whilst they're on the ramp, but he would never consider that he maybe should wear a helmet just in case he bumps his head. Yet I'd be surprised if he hasn't bumped his head more often working than he has whilst cycling.
For a pretty accurate study when it comes to the overall effectiveness of helmets you need look no further than where they have been made compulsory. Australia for example. Here you have real world studies which have been carried out over time frames which give very accurate data. This can of course be looked at both before and after compulsion for some very real results.