There was another agency, other than NCAP that I read about who rate car safety, but they do it on the basis of real world crashes, – so as well the physical protection the car offers it also factored in how likely the car is to crash. That can be a mix of the car itself and the people who drive them.
Big 4x4s for instance offer a lot of passenger safety, however they are also more likely to crash, partly because they handle badly and partly because drivers feel safer in them and take bigger risks as result.
It also revealed the effect of age – so it revealed how safe a car is 10 years down the line compared to when it rolled off the production line – and how a bit of fatigue and corrosion can undermine a car’s integrity in a crash
Trouble is – I can’t remember what that other agency was