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Expertise Rating
This is not my work. The original article may be found at:
http://forums.worldofwarcraft.com/thread.html?topicId=5103811788&sid=1
Expertise Rating
Tanking
Expertise is highly desired in tanking because it helps to prevent special attacks from being dodged or parried. For example, at 20 expertise (or 79 expertise rating at level 70), you will reduce the chance that an equal level mob can dodge or parry your attacks by 5%, This allows about 10% more of your swings to hit, increasing your threat generation.
More importantly, expertise also works as a mitigation stat, since when an enemy parries he gains a 40% attack speed increase towards his next swing (making it almost an instant double-hit). Therefore, reducing enemy parries is an important way of reducing incoming overall damage as well as burst damage. Boss parries coupled with boss special attacks are particularly deadly combinations, and have a nefarious history of wiping many appropriately-geared raids.
Note that warriors can gain 2/4/6 points of expertise (that's actual expertise, not expertise rating) by picking up the Defiance talent in the third tier of the Protection tree.
Paladins can get 1-5 points of expertise from Combat Expertise, in the sixth tier of the Protection tree.
DPS
Melee DPS also benefit from expertise. With the proper amount of expertise, as long as you're behind your opponent, your attacks will NEVER miss (with Max Hit Rating and Max Expertise rating, your attacks won't "Miss" or be "Dodged")
Weapon Skill
Expertise replaces weapon skill and is not limited to a particular type of weapon. i.e. there is not a separate expertise rating for axes and two-handed swords; the same table applies to both equally.
Expertise against Bosses
Since a boss-mob is calculated as level 73 mob its dodge is increased by 3*0.2% = 0.6% up to 5.6%. To negate 5.6% dodge, 22.4 (round this UP to 23) points of expertise or 91 points of expertise rating are needed.
Parry rates are unknown at this time but are estimated to be higher (between 10-15% or ~40-69 expertise/~160-273 expertise rating) and are probably variable from one boss to the next.
++++Expertise rounds down. Partial amounts of Expertise do nothing.++++
Base Melee Parry & Dodge: 5.6%
1 Expertise = expertise rating / 3.95
1 Expertise = -0.25% Dodge and -0.25% Parry
When you reach 91 expertise rating, your attacks will never be dodged. Melee attacks can still miss. If you reach both your hit rating cap and 91 expertise, your melee attacks will never miss or be dodged.
The following is the amount of expertise rating you need to minimize dodges for raid boss fights, depending on your class and talents.
Druid (Melee)
Base: 91
Rogue
Base: 91
w/ Weapon Expertise: 52
Shaman (Melee)
Base: 91
Warrior
Base: 91
w/ Defiance: 68
w/ Weapon Mastery: 76
w/ Defiance + Weapon Mastery: 52
Paladin (Melee)
Base: 91
w/ Combat Expertise: 72
http://forums.worldofwarcraft.com/thread.html?topicId=5103811788&sid=1
Expertise Rating
Tanking
Expertise is highly desired in tanking because it helps to prevent special attacks from being dodged or parried. For example, at 20 expertise (or 79 expertise rating at level 70), you will reduce the chance that an equal level mob can dodge or parry your attacks by 5%, This allows about 10% more of your swings to hit, increasing your threat generation.
More importantly, expertise also works as a mitigation stat, since when an enemy parries he gains a 40% attack speed increase towards his next swing (making it almost an instant double-hit). Therefore, reducing enemy parries is an important way of reducing incoming overall damage as well as burst damage. Boss parries coupled with boss special attacks are particularly deadly combinations, and have a nefarious history of wiping many appropriately-geared raids.
Note that warriors can gain 2/4/6 points of expertise (that's actual expertise, not expertise rating) by picking up the Defiance talent in the third tier of the Protection tree.
Paladins can get 1-5 points of expertise from Combat Expertise, in the sixth tier of the Protection tree.
DPS
Melee DPS also benefit from expertise. With the proper amount of expertise, as long as you're behind your opponent, your attacks will NEVER miss (with Max Hit Rating and Max Expertise rating, your attacks won't "Miss" or be "Dodged")
Weapon Skill
Expertise replaces weapon skill and is not limited to a particular type of weapon. i.e. there is not a separate expertise rating for axes and two-handed swords; the same table applies to both equally.
Expertise against Bosses
Since a boss-mob is calculated as level 73 mob its dodge is increased by 3*0.2% = 0.6% up to 5.6%. To negate 5.6% dodge, 22.4 (round this UP to 23) points of expertise or 91 points of expertise rating are needed.
Parry rates are unknown at this time but are estimated to be higher (between 10-15% or ~40-69 expertise/~160-273 expertise rating) and are probably variable from one boss to the next.
++++Expertise rounds down. Partial amounts of Expertise do nothing.++++
Base Melee Parry & Dodge: 5.6%
1 Expertise = expertise rating / 3.95
1 Expertise = -0.25% Dodge and -0.25% Parry
When you reach 91 expertise rating, your attacks will never be dodged. Melee attacks can still miss. If you reach both your hit rating cap and 91 expertise, your melee attacks will never miss or be dodged.
The following is the amount of expertise rating you need to minimize dodges for raid boss fights, depending on your class and talents.
Druid (Melee)
Base: 91
Rogue
Base: 91
w/ Weapon Expertise: 52
Shaman (Melee)
Base: 91
Warrior
Base: 91
w/ Defiance: 68
w/ Weapon Mastery: 76
w/ Defiance + Weapon Mastery: 52
Paladin (Melee)
Base: 91
w/ Combat Expertise: 72