The above posts are correct. Quite some time ago I got confirmation on this exact subject from one of the old devs.
When you are attacked, you first get a roll regarding skill related defenses (parry/bushido/etc). If you have none of those type of skills, you obviously fail that check. Then the game rolls for your DCI chances versus your attackers skill related attack chances, and finally their HCI. Quite obviously, the higher your DCI is, the better chance you have of winning this series of rolls.
At no part of the equation does dex come into play. Dex only affects swing rate, bandage rate, etc.
Hope this helps.
