Stats and their correlations...

Strength Increases melee attack power and damage blocked with a shield 1 Strength = 2 Attack Power = 0.15 DPS
(Shield block formula required!)
Agility Increases Critical Hit rate, Dodge rate, and Armor 1 Agility = 0.05% Critical Hit rate (at level 60)
1 Agility = 2 Armor
Stamina Increases Health 1 Stamina = 10 Health
(Note: Stamina gained at level up does not increase Health)
Intellect Increases Mana, and Spell Critical Hit rate 1 Intellect = 15 Mana
(Note: Intellect gained at level up does not increase Mana)
1 Intellect = 0.01% spell critical rate
Spirit Increases Health and Mana regeneration rate (Formula required for Health and Mana regeneration!)
Defense   20 Defense = 1% Dodge + 1% Parry + 1% Block
Armor   100 armor = 0.57% damage reduction