Combat rating increases Melee DPS , and are gained by Strength, Dexterity, Armor, Weapons, Buffs and by Potions. Strength gives combat rating and higher DPS to all melee classes except Assassin and Ranger, as these get their combat rating through Dexterity.
1 point in strength increases Combat rating when using melee Weapons (except Daggers ) by 3
1 point in dexterity increases Combat rating with Ranged Weapons and daggers by 3
It is said that 12 Strength or 36 Combat Rating equals roughly 1 DPS