Base Precision has a displayed Hit Chance of 70%. Base Swiftness has a base Dodge chance of 30%. If you put 10 points into Precision and raise the displayed Hit chance to 73%, the displayed Dodge chance will drop by 3%. So if you put 10 points into Swiftness to get Dodge chance back up, your Hit chance will go down by the same amount.
No idea if it's just a displayed value issue, but no matter what you do. The sum of the values of Hit Chance and Dodge never goes above 100.