When you work out the answer to that, you will be able to tell us why Prior still doesn't get a shout for England....
actually, ridiculous as it sounds, I can sort of see why he doesn't - his batting style is the perfect one to come in five down (should be four down) in Tests and accelerate the scoring with a wide array of off side boundaries but where does he bat in One Day cricket?
As an opener? He lacks the ability to hit over the in field and is comparatively one sided so the bowling captain can to a degree close him down.
In the middle order (5/6) - he's not a six hitter at that level, and again his boundary shots are all in one direction so he's easy to tie down.
Lower order? Well, yeah, theoretically he could do so - but when there is so much cricket being played, it seems silly to have him batting there when he could have a rest and someone esle who might be able to fill the roles is tried.
Of course the flaw in this argument is that Foster, Davies, Kieswetter, Mustard et al have all been found slightly wanting...