Technical Formulas

Armor

Armor reduces physical damage done against you by a certain percent. It depends on the level of the monster (or player) hitting you. Your own level doesn't matter. By hovering your mouse over Armor on your Character screen, you can see the value of this reduction for monsters that are at your current level.

This percent reduction will actually fall as soon as you gain a level if you're still wearing the same armor. You haven't lost anything, it's merely showing you that your armor isn't as effective against monsters one level higher than you used to be.

%Reduction = Armor / (Armor+400 + 85*Level)

I think the graph I made is a heck of a lot more useful to understand how it works: http://www.calloffate.com/forum/uploads/Alastriona/2005-05-01_235722_armor.jpg

(I'd like to get a local copy of this image. I am a member of the site to which I'm linking and author of the post of which this is an excerpt. -- Alastriona)

Armor and Dodge

The goal is to compare the changes in survivability of increasing dodge chance to increasing armor points. We will calculate effective health pool as a function of the current unmodified health, armor and dodge chance percent

y: Dodge Percent

x: Armor Points

C: Current Unmodified Health

f(x, y) = Effective Health Pool

f(x, y) = C * (1 + x/5500) / (1 - y/100);

f(x, y) = (C/55) * (5500 + x) / (100-y)

df/dx = (C/55) / (100 - y)

df/dy = (C/55) * (5500 + x) / (100 - y)^2

Assume we increase dodge by 1 and armor points by some constant D. We want to find the set of points (x, y) where both increases result in the same increase of f(x,y)

D * df/dx = df/dy, which can be simplified to: D = (5500+x)/(100-y)

That is, for any current value of dodge and armor, you get the same benefit increasing dodge by 1% or your armor by (5500+CurrentArmor)/(100-CurrentDodge)

For example, given AC = 10000 and Dodge=15% you need to increase armor by 182 to achieve the same benefit that 1 extra percent of dodge gives you. Substitute your current values to get your current breakpoint.

This is, of course, ignoring the various real-life shortcomings of dodge as mitigation method. Also note that AC here is AFTER modification by your bearform bonus.

Defense Skill

Each point of +Defense adds 0.04% to Parry, Dodge, and Block.

This means +25 Defense will grant you an extra 1% Parry, Dodge, and Block. The formula has been tested to be the same for both Hunters and Paladins. It's probably constant across all classes. Rogues are most likely to have a differing formula.

Defense has additional rumored effects: The following four effects of Defense were supposedly posted by a CM on WoW's European forums. A link to the official post would be nice.

Increases the chance of being missed by an attack.
Increases the chance to dodge, parry, and block.
Decreases the chance of being affected by a critical hit.
Decreases the chance of being affected by a "crushing blow". Creatures that are higher level than your character can land crushing blows that deal increased melee damage. The chance of a crushing blow increases as the level difference between you and the opposing creature increases. Players never deal "crushing blows", only creatures.

Magical Resistance

When an offensive spell is cast, the target has two seperate chances to resist the attack.

First, there is a roll based purely on the level difference between the caster and the target. If the target is significantly higher level, the spell will usually fail completely. If the target is significantly lower level, the spell will very rarely fail. This first roll is why spell casting players have such a hard time landing spells consistantly on all monsters a few levels higher. In PvP combat, it is much less of a factor. A level 10 Mage can very often land polymorph on a level 60 player.

Formula needed for the first roll.

Second, there is a roll based on the level of the caster and the resistance stat of the target. Notice that the level of the target is not a factor in this roll.

Average Resistance = (Target's Resistance / (Caster's Level * 5)) * .75

Average resistance may be no higher than 75%. Of course, what it takes to reach 75% average resistance depends on the spellcaster's level. Against a level 1 spellcaster, it would take a resistance stat of 5. Level 20 would take 100 resistance. Level 50 would take 250 resistance. Level 60 would take 300 resistance. Level 63 would take 315 resistance.

Why is it called "average resistance?" For spells that don't cause immediate damage, you'll either totally take the hit or totally avoid the hit. The average resistance is the chance you'll totally avoid the hit. Adding the word "average" is a little redundant in this case.

However, when spells do cause immediate damage, it's not just a full hit or full miss situation. Damage spells be resisted for 0%, 25%, 50%, 75%, or 100% of their regular damage. Your average resistance can still be anywhere betweeen 0% and 75%. If your average resistance is maxed out, then there's a really good chance of 75% of the spell's damage to be resisted. There's also a fairly good chance of 100% of the spell's damage being resisted. A slightly lower chance of 50% of its damage being resisted. Small chances of only 25% or even 0% of the damage being resisted. It's a weighted average. Visualize it as a bell curve around your average resistance.

Average Resistance vs Level 60 Spellcasters

Resistance Stat	0	25	50	75	100	125	150	175	200	225	250	275	300
Average Resistance	0%	6.25%	12.5%	18.75%	25%	31.25%	37.5%	43.75%	50%	56.25%	62.5%	68.75%	75%

Also see Blizzard's Page on Resistances

Spirit

Spirit increases the rate of health and mana regeneration.

Health regeneration only takes place out of combat. Mana regeneration may take place in combat, but not for five seconds after completing a spell cast.

Current formulas operate in the form of (Spirit/X) + Y. X and Y vary per class.

Class	Mana regeneration
Priest	(Spirit/4) + 13
Mage	(Spirit/4) + 11
Warlock	(Spirit/4) + 8
Druid	(Spirit/5) + 15

Attack Power and Crit chance

Note: I'm not sure of the numbers that I put a ? by, if someone else does, please add them! :)

MAP = Melee Attack Power

RAP = Ranged Attack Power

Hunter

1 MAP = 1 Agi or 1 Str

2 RAP = 1 Agi

1 Crit = 52 Agi (or is it 53?)

Rogue

1 MAP = 1 Agi or 1 Str

1 Crit = 25 Agi (?)

Warrior

2 MAP = 1 Str

1 Crit = 20 Agi (?)

Paladin