Get the hell out of Dodge!

(aka How does Agility stack up to Dodge for damage reduction/prevention?)

Many people have been asking me to update my Agility v. Dodge comparison for Icecrown, and this time around I'd like to include the other classes so that we have meaningful results for all 4 tanks. The code for this simulation can be found here:
calc_dodge_v_agil.m.

I'm nowhere near the "optimum" gear load-out right now, but for the sake of argument we'll again use my current armory to pull stats from.

28,910 armor unbuffed
869 Defense Rating
780 Dodge Rating (30.39%)
204 Parry Rating (19.61%)
155 Agility.


I'll get 230 agi from raid buffs (SoE totem, MotW). Raid-buffed my agility should be 423 after kings (382*1.1).
I'll also get 1807 armor from Improved Devotion aura, 230*1.1*2=506 armor from the agility buffs, and 152*0.1*2=30 armor from the 15 agility I get from the interaction of Kings and my base agiility. That leaves me with a total of 31,254 armor raid buffed.

Using avoid_dr.m, which calculates avoidance after diminishing returns, this gives me the following raid-buffed avoidance:
Dodge: 23.0489%
Parry: 9.6100%
Miss: 5.0430%
Total: 37.7019%

Using avoid_dr.m again, I'll calculate my avoidance with 10 additional dodge rating, without changing the other inputs. This simulates the amount of dodge you get from a 10 dodge rating gem.

• Dodge % goes up to 23.1747, an increase of 0.1258%.

After kings, 10 agility becomes 11 agility. I'll calculate my avoidance again, but this time adding 11 agility rather than 10 dodge:

• Dodge % goes up to 23.1535, an increase of 0.1046%.
• We also gain 22 armor.
• That 11 agility also gives us crit, at the rate of 1% crit for 52.0833 agility, for a total of 0.2112% crit (equivalent to 9.6954 points of crit rating).

So the relevant conversions we want are:
10 Dodge Rating = 0.1258% Dodge
10 Agility = 0.1046% Dodge, 22 Armor, and 0.2112% crit


To calculate incoming damage, first we have to add in sources that aren't subject to DR, which is 10% dodge, 10% parry, and 5% miss. Thus we end up with our overall base avoidance values:
Dodge: 33.0489%
Parry: 19.6100%
Miss: 10.0430%
Total: 62.7019%

Chill of the Throne decreases our dodge to 13.8951%, and our overall avoidance to 42.7019%.

ncoming damage gets reduced as follows:

If the bosses dodge-able attacks do X damage per second, and you have avoidance A then before either gem is added, you're taking X*(1-A) damage per second due to the attacks you don't avoid. If you increase your avoidance slightly from A to A' = A + dA, it reduces damage taken to X*(1-A'). So by adding the dodge gem you've reduced your incoming damage by a multiplicative factor of (1-A') / (1-A).

Mitigation from armor M reduces damage in a similar way, from X to X*(1-M). M is defined as:
M = (Armor/(Armor+16635)
Again, if you increase your armor such that your mitigation goes up to M' = M + dM, your damage intake drops to X*(1-M').

Migitagion and avoidance are multiplicative - in other words, if you have avoidance A and armor mitigation M, your overall damage take is X*(1-A)*(1-M).

We have two situations to consider:

• Base Configuration: A0=42.7019%, M0=65.2634%
• +Dodge/Stam gem: A1=42.8277%, M1=65.2634%
• +Agil/Stam gem: A2=42.8065%, M2=65.2794%

The dodge gem reduces intake by (1-A1)/(1-A0) since M1=M0. This works out to 99.7804%, or a 0.2196% reduction in damage intake.

The agility gem reduces intake by (1-A2)/(1-A0) * (1-M2)/(1-M0). The first factor works out to 99.8174%, and the second works out to 99.9541%, for a total of 99.7716%. The avoidance and armor gained from the agility gem individually give you less reduction than the avoidance of the dodge gem, but combined they end up giving you slighty more reduction than the dodge gem does. The net reduction works out to be a 0.2284% reduction in damage intake.

The ratio in this case works out to be 1.0426, or 104.0% So in terms of incoming damage, the Agility gem is 4% more effective than the pure dodge gem, and also gives you critical strike rating.

I also ran a parry gem just to see how it stacked up, and despite the fact that I'm deep into the region where I get more avoidance from a parry gem (check: (dodge-10)/(parry-10) = 2.4865 for this gear set), the parry gem is about 15% better than the dodge gem, and 11% better than the agility gem. So you will get slightly more damage prevention from a parry gem, though in that case none of it comes in the form of effective health.

Just to test the scaling, let's see how this varies with dodge rating:

As you can see, Agility just gets better as you gain more base dodge rating.

Now let's see what happens as our base armor goes up:

Agility gets weaker as you gain armor, finally dropping below 100% at around 42.6k armor (fully-buffed). Note that once we hit the armor cap (49905 armor fully-buffed), the armor contribution of agility is no longer giving us any benefit, so the value of agility drops back to the 83.1% value expected based on our agi->dodge conversion ratio.

Practically, this means that once we're getting close to the armor cap, we're getting close to the situation we have outside of ICC, where agility is around 98% as good as dodge rating. Most of us considered this a good trade anyway, since we got some free threat and some of the damage reduction came in the form of extra EH. Once you're over the armor cap, there's no reason to gem agility over avoidance for survival.

TLDR Summary
In Icecrown Citadel:

• Each point of Agility is 83% as effective as a point of dodge rating for avoidance. (i.e. 10 AGI ~ 8.31 Dodge rating)
• Each point of Agility is around 4% more effective at reducing average incoming damage as a point of dodge rating
• Each point of Agility also gives you almost 1 pont of critical strike rating.
• In general, if you're going to match a red socket for Icecrown progression, use an Agility/Stam gem rather than a Dodge/Stam.
• If you're at or above the armorcap, agility drops back down to 83% the damage reduction of an avoidance gem, with no added survivability benefit.

Outside of Icecrown:

• Each point of Agi is still 83% as effective for avoidance, but is now only 98% as effective as dodge rating for reducing incoming damage. Still a worthwhile trade though, since it gives you some of that reduction in the form of EH, and gives you threat as well.