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The New Effective Health Formula

As we discussed before the patch, there have been some changes to armor on items. Bonus armor’s item point cost has been drastically increased on all items except for trinkets, shield armor has been reduced, agility no longer grants armor, and the Engineering tanking benefit, Reticulated Armor Webbing, has been nerfed from 885 armor to 250 armor. Between the reduction in our personal armor, the removal of some armor raid buffs, and the relative nerf to the -AP debuff, we would expect to be taking a bit more damage on physical hits.

We would not expect to be taking this much more damage.

Happily, a Death Knight tank named Valen, of Temerity – Windrunner – Alliance, figured out what was wrong and posted it on the official tanking forums. I highly recommend you read the original post if you like theorycrafting, are interested in the details, or just like the visual of Algalon dual-wielding Lich Kings.

It turns out that Blizzard has already implemented the Cataclysm armor curve against enemies above level 80. As with all other stat curves, the damage reduction from armor curve is shifting downwards at the beginning of the new expansion, to help combat stat inflation. But unlike the avoidance stats, damage reduction from armor is calculated based primarily on the attacker’s level, not on the defender’s level. This means that we are suddenly undergeared for Wrath raid bosses: as far as our armor is concerned, we’re reckless level 80s fresh out of Wrath, trying to down level 83 elites from Hyjal.

Ghostcrawler was interested to hear about Valen’s findings, but it didn’t sound like he considers it a problem, or at least not a problem worth addressing; so we’re just going to have to deal with this for now. The question is naturally, what’s the best way to handle it? How has this changed the relative importance of stamina and armor, and what should we be stacking?

Well, the new armor formula is EHlv80 = H(armor+21735)/21735(1-effectreduction) for Wrath bosses in 4.0.1. (My work is included at the end of the post, if you’d like to doublecheck it).

As an exercise, let’s consider whether an self-buffed Lindentree would be better served sticking with the Corroded Skeleton Key or switching to Glyph of Indomitability on a 100% physical fight outside of ICC – let’s say Baltharus. Her self-buffed health and armor with the key are 53092 and 27990 respectively, and since Vigilance can’t be placed on yourself, her damage reduction from effects is only 10% (defensive stance). This works out to an EHkey of 134958. (EH numbers should always be truncated, as there’s no such thing as a partial point of damage.)

By switching in the Glyph, Lindentree would gain 1792 armor (assuming Toughness in Cataclysm, as in Wrath, does not apply to bonus armor) and lose 1.05*1.15*228*10 health (5% increase from plate specialization, 15% from Vitality), for a total of 50339 health and 29782 armor. Her EHglyph will be only 132572, so she should stick with the key.

In order to maintain the same EH in switching from the key to a flat armor trinket, Lindy would have needed a trinket with 2719 armor.


The new armor formula, as provided by Valen, is Reduction = Armor / (Armor + MobLevel * 2167.5 – 158167.5) . So for example, with Lindy’s armor (without any buffs, armor trinkets or procs, but with talents) her base physical damage reduction from armor vs an ICC raid boss is 27990/(27990 + 83*2167.5 – 158167.5) = 27990/49725 = 56.29% . Additional damage reduction from defensive stance (10%) brings total physical damage reduction to 1-((1-reduction from armor)*(1-reduction from effects)) = 1-(.4371*.9) = 60.66% total physical reduction, without the 3% Inspiration/Vigilance/etc. reduction. Since EH is health/(1-physical reduction), our new EH formula for a Wrath raid boss is

H/(1-(1-((1-armorreduction)*(1-effectreduction)))) = H/((1-armorreduction)*(1-effectreduction)) = H/(1-effectreduction) * 1/(1-armorreduction).

1/(1-armorreduction) = 1/(1-armor/(armor+21735)) = 1/((armor+21735-armor)/(armor+21735)) = 1/(21735/(armor+21735)) = (armor+21735)/21735 .

So EHlv80 = H(armor+21735)/21735(1-effectreduction) for Wrath bosses in 4.0.1.

For Cataclysm bosses, substitute 32572.5 as the constant in the formula, for EHlv85 = H(armor+32572.5)/32572.5(1-effectreduction) .

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  1. December 11, 2010 at 9:35 pm

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