my interpretation of the notes for version 5.0 is that both you and the mob have a flat 5% chance to avoid damage, or 'miss'. After that, whichever of you has higher DEX gains additional 'dodge' chance whilst the other does not. (XXX is too dexteritous for you - note for the devs, dexteritous isn't a word. You want 'Dextrous'

)
This is all theory, mind, but I would imagin it to work something along these lines:
Yourdex:mobdex <---as ratio
2:1 = 10% for you to dodge
3:1 = 20% for you to dodge
6:1 = 50% for you to dodge
1.5:1 = 5% for you to dodge
1:1 = nobody dodges
1:2 = 10% for the mob to dodge YOU.
Thats my theory based on precicely 0 sample data, so really take it with a grain of salt. I think thats how the PATTERN might work but the hard numbers will almost certainly be different.