I think Aloarjr810 hit the nail on the head with his descriptions of each position. The only thing I would add is you really need to look more at the people then the averages. The anchor bowler need to have the right make up, sort of like a closer in baseball. They have to want to ball in their hands at the end of the game. They have to be able to deal with the pressure of throwing the last frame with a game on the line. And, maybe even more important, they have to have a short memory and quickly forget about the times where they don't come through, as they may needed again the very next game.