Ah, OK, I think I know what you are talking about. I think you are talking about "critical chance" in the stat screen, don't you? Aside from the resistances it is the only percentage number. Well, critical chance is NOT a chance to hit - it is a chance to make a critical hit to the enemy IF you actually hit it (which is based on your chance to hit). A critical hit deals extra damage to the enemy.
Below the critical chance, you can actually see the offence and the defence ratings. These are the numbers (among other parameters) which are resposible for your chance to hit and to be hit.
