Notice - This guide needs to be updated. There are clearly encounters where Avoidance is superior to Effective Health, such as Prince in Karazhan. Will have an update ASAP. - Mar 28 '08
Let's establish what Effective Health and Effective Stamina are. This is basically a measurement of how much raw damage a creature has to deal to kill you. It is a measurement of Armor and it's relation to Stamina.
What many tanks do not understand is just how much damage a creature is dealing to them. I didn't realize it until I studied Patchwerk -- who dealt 22,000 to 29,000 raw damage to our tanks with every Hateful Strike.
Effective Health is the measurement of how much breathing room your healers have to keep you alive assuming all other factors fail -- assuming you do not avoid or block attacks or have a mana shield active. Effective Health is important for tanking heavy hitting creatures because of Murphy's Law -- if you can have long strings of not Dodging an attack, it will definitely happen. Raid tanking, ultimately, is about stability.
Life Per Stamina (LPS) & Effective Life Per Health (ELPH)
The equation to determine Life Per Stamina is (Special thanks to Ilmare):
AC Mitigation LPS ELPH
0 ___________________ 0.00% _____ 10 : 1 ____ 1.00 : 1
10,000 ______________ 48.64% _____ 19.4 : 1 ____ 1.94 : 1
12,000 ______________ 53.20% _____ 21.3 : 1 ____ 2.13 : 1
13,000 ______________ 55.18% _____ 22.3 : 1 ____ 2.23 : 1
14,000 ______________ 57.01% _____ 23.2 : 1 ____ 2.32 : 1
15,000 ______________ 58.69% _____ 24.2 : 1 ____ 2.42 : 1
16,000 ______________ 60.25% _____ 25.1 : 1 ____ 2.51 : 1
17,000 ______________ 61.69% _____ 26.1 : 1 ____ 2.61 : 1
20,000 ______________ 65.45% _____ 28.9 : 1 ____ 2.89 : 1
25,000 ______________ 70.31% _____ 33.6 : 1 ____ 3.36 : 1
Mitigation is determined through this equation (Special thanks to Satrina):
1 / (1 - Mitigation)
Effective Life Per Health is determined simply by dividing the Stamina numbers by 10.
Mitigation (70) = -----------------
Armor + 10557.5
Mitigation (73) = -----------------
Armor + 11960
Special Note: Please keep in mind that every 1,000 Armor produces precisely the same increase in Effective Life that the last 1,000 Armor did. Satrina has covered this in-depth, but it can never hurt to say it again -- Mitigation is subject to diminishing returns but Armor is not. Armor provides a linear increase in life expectancy. Stamina scales with Armor.
Link to Satrina's information: The Mathematics of Armour and Diminishing Returns
The first hypothetical is for a tank who has chosen primarily to focus on Stamina and Armor over Avoidance and Defense. The following are reasonable attributes for this Warrior, assuming he has been through Karazhan but not further:
If we run with the above Effective Life Per Health ratio, this is our end result:
13,000 * 2.32 = 30,160 Effective Life
Let's take the standard number of people who tend to itemize Avoidance and Defense equally, or sometimes in greater standing than Stamina and Armor:
Running the same equation:
12,000 * 2.13 = 25,560 Effective Life
That's a 5,100 difference in raw damage between two tanks who think they are at similar standing. Or, to put it in more familiar terms, that is the difference between a Warrior comfortably tanking a lvl 70 Patchwerk and a Warrior regularly getting one-shot by same.
Now let's run some numbers to see how very basic consumables affect tanking. I'll use just a Flask of Fortification and a Stoneshield Potion on our first tank.
14,500 * 2.51 = 36395 Effective Life
This means that with just these two potions, a tank has increased the damage he is able to withstand more than 17%.
1) Even though this may sound obvious, it needs to be repeated that every increase in Armor gives linear and potent scaling to the effectiveness of Stamina. Every increase in Armor is a direct increase in the effectiveness of Stamina; every increase in Stamina is a direct increase in the value of Armor.
2) With the above in mind, the Vitality talent needs to be evaluated for total merit. While a tank may complain that Vitality only gives them a 600 health increase, they fail to recognize the effective health gained is generally going to be more than twice that.
3) Solid Star of Elune gems should be viewed under the same principle. While Avoidance gems such as +Defense and +Dodge gems will always offer a precise, static damage reduction, a Solid Star of Elune can scale in many raid situations to be the equivalent of over 30 Stamina.
4) There are a few people who have made comments regarding why Avoidance stats may be better. One poster mentioned that he would rather have 10% Dodge from gems than Stamina. The equivalent of that 10% Dodge would be 2,835 HP, which, given his Armor, would in turn increase his Effective Life by over 6,000. In other words, if he focused on Stamina, he could take hits from a full raid zone beyond his current capability. Need proof? Look at the Armory profiles from tanks in the top-progressing guilds worldwide.
5) If you have enough Stamina, the most effective means of increasing survivability as a tank is to increase Armor at the cost of other attributes. In particular, when facing an enchant choice such as that of +12 Dodge to Cloak or +120 Armor to Cloak, a Stamina heavy tank will definitely find greater benefit from the +120 Armor.
6) Increasing Stamina is not always the best method to increase Effective Health. When making a choice between Armor and Stamina upgrades, you will often find that Armor will give you a higher Effective Health than Stamina.
7) The choices between Stamina/Armor and Defense/Avoidance should only come when evaluating near-equal pieces of gear. Gems are a generally good subject because they are naturally equal in item level. One smaller point to remember is that Avoidance always takes a 7% hit on overall damage reduction due to the combat table -- 1% Dodge is actually only 0.93% damage reduction once the additional damage from Crushing Blows is factored in. When dealing with items of significantly different item levels, common sense applies.
8) It's not about balance. Like tanking weapons, where faster is always better, when tanking new encounters, Stamina and Armor are always better. The set you use to tank new content should always have the highest Effective Health possible. As you get comfortable with an encounter, you wear more Damage Reduction gear (Armor/Defense/Dodge). This is a hard and fast rule.
Like always, this is not written to help the casual tank. It is written only for the tanks who are pushing through content beyond their gear level and wish to do it more effectively. This is what the Stamina Warrior is, and I write this just as passionately as I did over a year ago with "Miles to Go."
I deeply respect people like Emeraude, who championed the Defense/Avoidance/Agility/Armor tank theory. I remember seeing a great Twin Emperor's combat monitor from Emeraude. I fall squarely into the Stamina/Armor/Strength/Block Value camp, and many months ago we used to have great arguments on these forums.
I understand the irony of having a Druid post an article about Stamina and Armor. One of the old catchphrases of these forums was that Avoidance is what sets Warriors apart from Druids. I will make this absolutely clear -- Avoidance is good (especially Dodge, as Wanderlei has clarified). You will find great pieces of incredible Avoidance gear such as Boots of Elusion. Defense is good. You want and need these stats, and you will get them with much of your tanking gear.
With tanking new content, one rule is important -- it's not about taking less damage; it's about being able to take more damage.
Shield Block Value and additional Effective Health
The Effective Health shown on this website is reliable and accurate. However, there is an additional, scaling bonus to your Effective Health in the form of Shield Block Value. This is the secondary scaling of Shield Block Value (the primary scaling is already included in the equation here).
In addition to increasing your Effective Health by a base amount -- exactly like Health -- it also decreases a percentage of damage taken. However, the percentage decrease cannot be quantified without detailed information regarding the attack speed, average damage, and maximum damage of your enemy.
Consider the difference between going into a 5-man or Heroic instance with 500 Block Value and going into a fully realized raid boss encounter with same. The percentage reduction -- and your total Effective Health -- will be different for each encounter. Where you might gain limited advantages to Mitigation against some bosses, others, such as the Prince in Karazhan, will yield far better returns with Block Value. In some cases, especially in world farming, Effective Health can multiply several times over due to a state of near-invulnerability.
Shield Block Value is the stat with the highest potential in the Effective Health equation. It shares a unique relationship with both Health and Armor. Armor is a curved mechanism for increasing Mitigation; Shield Block Value, however, is a linear mechanism for increasing Mitigation. In other words, Shield Block Value does to Mitigation what Health does to Life.
Shield Block Value gains the same benefit as Health when factoring in Armor. As Armor increases, the value of each point of Shield Block Value increases. Then, as the value of Shield Block Value increases from Armor, the value of Health and the impact on Effective Health increases unpredictably -- unless we know the incoming damage values.
However, keep in mind how limited Shield Block Value is on gear. Reaching 1,000 Shield Block Value, for instance, is virtually impossible without the use of trinkets or the Tier 5 Shield Block Value bonus. Blizzard most likely itemizes large amounts of Block Rating -- a near worthless stat for Warrior raid tanks -- to keep item levels and potential Block Value in check. Unfortunately, this also extends to gem choices, and it is this reason -- not potential Shield Slam damage -- that we are unlikely to see many Block Value gems on the horizon.
Complex? Sure. Bottom line: don't write Shield Block Value off for it's Mitigation value.
Thus, Avoidance also helps reliably keep Effective Health high. By increasing Avoidance such as Dodge, you simultaneously decrease the chance of incoming attacks not being avoided or blocked. Indeed, increasing Avoidance will keep more Shield Block charges active for longer, and with enough of it, you become virtually immune to Crushing Blows in most encounters.
This isn't to say that you need to go gem everything with Avoidance. Please note the wording in bold -- it will not increase Effective Health. It will only help stabilize your rate of effective Shield Blocks, which in turn allows Block Value to be reliably factored in. Heavy Avoidance is only important for some boss fights -- boss fights you would probably use some Avoidance gear for in the first place. Also, Warrior equipment is already unusually weighted with Avoidance stats, and you gain plenty through normal gearing.
The original thread and all of the outstanding responses can be found here:
WoW Forums -> Effective Health, Armor, and Gemming/Gearing