The research has come to a conclusion: there is no significant safety benefit to wearing a helmet. More studies will obviously be read with interest, but it's clear that if there is a beneficial effect it is very small and hard to detect. If helmets were brilliant at protecting against head injuries then we would have discovered that by now.
Accident reports can not show you whether a helmet would have helped protect someone from a head injury. Only statistical analysis of large numbers of accidents can do that.
The rest of your post amply demonstrates that you have no understanding of statistics.
I apologise I'm winding you up and I don't mean to, Of course your right in that to understand the big picture you need good statistical data, to be able to allocate priorities, make laws , to decide which are the real issues in cycle safety. - of course your right.
But at an individual, personel level all these statistics are going to do you no good, - because when your knocked off your bike and heading earthwards at a great rate of knots , statsticaly this shouldn't be happening and statiscly if my head hits the ground I will be fine - isn,t going to save a lot of pain , flesh and blood. including premature balding as hair doesn't grow on scar tissue.
And I,m not saying the helmet will save you, you would be suprised how much a wooly hat will do to reduce superficial damage as much as a helmet.
At our level I think the accident reports are more illustrative of a helmets worth.