Heres another thought - not all factors can be accurately predicted by statistical analysis.
For example - because many young drivers buy small cars that are meant to be cheap to insure / run (i.e. Saxo etc), and then crash them - insurers often quote more for such cars instead of the next models up (i.e. something like an Astra / Focus), as these are crashed less.
However, because of this many young drivers can no longer afford to insure the smaller cars - and instead go for something slightly larger. The risk profile is exactly the same (and as the cars are slightly faster with a higher mass, arguable more so), but the premium is less.