Wednesday, July 21, 2010

[General]The dirty secret about armor

This is somewhat based on a post I made on tankspot a while back and references common tanking terms like Effective Health and Time to Live. If you don't know what these mean - read Aggathon's excellent treatise on these things over at Tankspot: Why we do what we do. There's nothing new there for many tanks familiar with these concepts, but it's a well-done document.

But, there's something it doesn't cover - and that's the advantages armor has over stamina. Or at least it doesn't cover it hugely. Similarly, it doesn't cover the advantages that resistance has over stamina in some circumstances.

Effective health is simply how much total incoming damage you could take at once. It is normally referring to physical damage (noted as PEH, or physical effective health) and is simply the following:
health / (1-armor reduction)

So if you have a 50% armor reduction and 50,000 health, you have a PEH of 100,000 - meaning you can take 100,000 physical damage (before armor reduction) before you die. Now, other things like general resistance to all damage (such as protector of the pack) fall in here too, but ultimately it doesn't matter; the important thing to consider is effective health combines the reduction in damage with the amount of health you have.

Similarly, you can look at magical effective health (MEH) as:
health / (1-reduction)

which factors in general resistances and specific ones. Note that for the purposes of effective health, you can't take into account chance; if something could happen that's beneficial (like a block or dodge or SD proc), effective health assumes that it won't happen. Thus for resistance purposes you can take only the minimum resisted value.

So that tells you how effective health works. And you can combine the two values depending on the % of magical damage and physical damage you're expected to take at a given time, and optimize based on that. Now most folks will tell you - often rightly - that the best way to optimize for this is to always go for stamina, even over more armor - because health is in both physical and magical EH and benefits both. And that's true - but only for the calculation of how much damage you could ever take.

Where it gets interesting is in the notion of partial health. And this is where the dirty secret of armor comes in. While effective health is awesome, stamina only helps how much damage you can take at a given time; armor magnifies both how much damage you can take AND how valuable healing can be.

Let's take a very simple example that should be at least somewhat realistic - two tanks with precisely the same physical effective health. One tank has 50k health and 50% armor reduction and no other sources of reduction (or for our purposes they're the same as each other, so they go away) - so using the formula above they have 100,000 EH. The second tank has 40k health and 60% armor reduction, giving them also 100,000 EH (40000/ (1-.6)).

Now, we'll hit both of them with a hit that takes half their EH - a 50k hit. The first tank's health is now at 25k. The second tank's health is at 20k (50k *.4 = 20k). Still the same EH, right?

Now, let's heal them. We'll heal both of them identically for 10k health. This is where it gets interesting.
The first tank goes from 25k to 35k - and their EH is 70k.
The second tank goes from 20k to 30k. Their EH is now 75k. That's a 7% lead in EH over the first tank.

Let's give them another 10k heal:
The first tank goes from 35k to 45k. Their EH is 90k.
The second tank goes from 30k to 40k. Their EH is 100k - up to full. At this point the second tank has a 10% lead in EH over the first!

And that's the dirty secret of armor - and why armor is good. Because it improves the value of healing, partial healing on a tank, it increases the EH of the tank after they've taken damage but before they've been healed to full. That it also makes it more likely they can be healed to full is a nice side effect too. This seems somewhat obvious - since armor reduces damage taken, of course it reduces the amount of health needed to go to full - but the EH model doesn't often talk about partial healing or what happens when your tank is somewhat healed but not entirely. And the bigger the deficit and the larger the amount of heals it takes to get there, the more this becomes obvious.

Yet we don't often have the case where a tank takes damage and then sits there with no heals until they get all the heals at once. Many tank deaths happen because of a combination of lack of enough healing with a set of hits; this was what killed people on Algalon, as an example.

Now the side part of this is that since armor doesn't help with magical damage, this is obviously not as great for things with massive magical burst; in the above example the 40k tank has 40k MEH, and the 50k tank has 50k MEH, which is a big disadvantage. The neat thing though is that resistance math works exactly the same here as armor does - with similar advantages in partial damage and healability. And that means that resistance at certain steps becomes far more valuable than health due to how much damage you can reduce. We've seen this before with Sarth3D and with heroic 25-man Anub'arak, and it's been used nicely sometimes for Sindragosa as well. And resistance also gets a boost from simply being way better at increasing EH than health does; while you can get 110 stamina from a wrist enchant, you can also get about 5% resistance (or 50% of the way to 10% resistance), which is a much bigger boost to MEH than that 1300 health would be normally.

Anyway, hopefully this will give you some intuition as to why things like Unidentifiable Organ is good regardless of whether the stack wears off, or why Petrified Twilight Scale is awesome even with the proc being somewhat meh. It should also give you an idea of why bears were so ridiculous before this as far as being healable, especially back in the day of TBC.


Willowbear said...

Good post. One question I haven't been able to find a definitive answer for yet...what is the wotlk armor cap for us? The number that keeps popping up is 40k, but I'm not sure if that is a legit number or something propagated word of mouth.

Raid buffed I'm at almost 39k armor. Just like any other stat I'm concerned about waste due to being capped.

Kalon said...

Willowbear, the armor cap against a level 83 mob is 49,905. With certain procs (like black heart) and indestructible potions you can hit it, but not consistently.

Anonymous said...

Interesting post. It's always the tendency to go the stam route since it scales so well and everyone loves to see a large health pool - but this is a good reminder of the importance of not neglecting your armor.

Sometimes I wish armor was visibly transferable in some way, like stam is to health.


Rannasha said...

I quite agree with the content of this post. I feel that people focus too much on what exactly rolls out of the simple EH calculation and base their gear decisions on that.

I made a blog post a few months back about this and I think that EH assuming the worst-case-scenario is too pessimistic and for actual ingame purposes flat-out wrong. Since bosses always take a few seconds to kill you, there is always time for some healing to land. In any organized raid (and when you talk about min/maxing you can assume that your healers are at least semi-competent, otherwise why bother?) there should be HoTs on you and healers should be machine-gunning their direct heals. In addition, in alot of fights the dangerous moments can be easily anticipated and cooldowns can be used.

If you include the fact that there is always going be something in the form of healing, absorbs or damage-reductions active on you, the standard "naive" EH calculation goes wrong: It overestimates the value of stamina and underestimates the value of armor / resistances.

In practice, armor/resistances are alot more powerful than the "naive" EH calculation makes them appear, simply because the worst-case-scenario doesn't happen in a decent raid.

Gingershnaps said...


I'm trying to gather some data so I can make a post about our favorite talent Natural Shapeshifter. Could you please tell me what some of your stats are while you're in your feral gear? I need to know your (unbuffed) int, spirit, mana pool,and mana regeneration rates (casting/not or combat/not if that is how it works now).

Please and thank you!

Kalon said...

I can do that, Gingerschnaps - is this for live or Cata?

Gingershnaps said...


It would be your spellcasting stats from Cata. I did a big breakdown of Natural Shapeshifter and mana costs. I have an idea I'll be posting about here shortly which I'd love your input on.

Thank you kindly!

Anonymous said...

Great post. I was thinking of the same concept of why I like armor/resistance, except instead of talking of partial healing, I was going to use the acronym EHH (Effective Health Healing). Hehe, I crack myself up.