Unmitigatable Mitigation – the silent DPS killer

You may have noticed at times that some caster DPS will be jumping up and down the charts at times; sometimes they have high DPS but lower damage done, sometimes reversed, sometimes they will see their DPS vary by as much as 500 under pretty much identical circumstances. Many times this is bad luck (no crits), brainfarts (wrong buttons, clipping DoTs) or moving a lot in a fight. Partial Resistance pops up, and while it’s effects are seemingly low, over the course of long fights this adds up to quite an impressive number.

Disclaimer

This is not an excuse for low DPS, consider it more like a short explanation of this mitigation, and why you always seem to lose some DPS under identical conditions. It also helps to explain a bit why we have to consider this now instead of before, and why it affects some people more than others. It is also a bit of a personal soap box, trying to figure out if others have similar experiences.

Prologue

Before, we did not see this in our spells, but more often when checking your WWS parses or World of Log entries for your damage done you’ll find a sneaky little number called “resisted” pop up. This number can vary between 2% and 8%, and is the amount of damage that has been mitigated on the boss.

What is mitigation/Partial Resist?

Bosses have three defenses against the spells we cast on them. These defenses are in place to make sure that only on-par casters will be able to attack them properly, and to reduce some damage done to them while still allowing our full damage to count in PvP. In other words, they are anti-lowbie defenses and ensure that our PvE damage is not nerfed due to our PvP damage potential.

• Miss: Any spell cast on a boss-level mob has a base 17% chance to miss when cast by a level 80 character. This is because the boss is 3 levels higher than us, and this defense scales greatly with level. Misses can be completely negated by having any combination of talents, hit from gear and having a Draenei around equalling or exceeding this 17% number.
• Magic Resistance: Some bosses have an innate resistance to certain schools of spells, the equivalent of a raid member having an Aura of Fire Protection or a Prayer of Shadow Protection, for instance. This reduces the damage of that school partially, and could be (theoretically) negated by stacking Spell Penetration. In practice, this is not done and it is also too rare to find bosses of this nature to bother with it.
• Partial Resist: Another level-based resistance on bosses, this reduces all spell damage done to the boss by a certain percentage. An explanation is given here, in this Elitist Jerks thread – it is dated, but gives a good basic idea. Another example is this thread, which is what explains differences in WWS logs.

How much is mitigated

Every spell thus has a 6% chance of having is base damage reduced by some amount; this is always a multiple of 25%. Consulting the table on this Wowwiki page, we can deduce that damage is either mitigated by 25% or 50%. Which of the two you get seems a random chance again, part of the debate on whether the system makes 1 or 2 calculations every time you casta  spell at a target, but that is deep theorycrafting stuff.

What does this all mean?

It means that nominally about 2-4% of your spell damage is mitigated because of the innate spell resistance of boss-level mobs. This cannot be mitigated in any way, it’s always there, 2% per level the boss is higher than you. But for some classes it seems to be different than for others; when browsing through logs I found that often Mages were closer to 2%-2.5%, Moonkins at 3.5%-4%, and us Shadowpriests were most often at 4% or higher. One unlucky Shaman actually almost reached 5% total damage mitigated.

I first thought it was dependent on Crit%, because as stated in the last thread I linked, the resisted amount is calculated of your base damage, multiplied if you have a crit, but without taking any debuffs on the boss or flat damage bonuses on you into account.

An example:

You deal 1000 damage; 25% of this is resisted = 750 damage done
You deal 1000 damage; 50% of this is resisted = 500 damage done
You crit for 2000 damage; 12.5% of this (25% base damage) is rested = 1750 damage done
You crit for 2000 damage; 25% of this (50% base damage) is rested = 1500 damage done

The same number with a flat 10% damage boost on you would be:

You deal 1000 damage; 25% of this is resisted = 750 damage done +10% = 825 damage done
You deal 1000 damage; 50% of this is resisted = 500 damage done +10% = 550 damage done
You crit for 2000 damage; 12.5% of this (25% base damage) is resisted = 1750 damage done +10% = 1900 damage done
You crit for 2000 damage; 25% of this (50% base damage) is resisted = 1000 damage done +10% = 1100 damage done

In other words, this seems to reveal the following basic patterns:

• Resistance is measured against base damage
• Resisted amount can be 0%, 25%, 50%, randomly determined
• Crits are reduced less than base hits
• Flat damage modifiers seem not to be mitigated

Conclusion

The reason we never saw this before, is because we never relied on Crit before; we simply did our damage, took the mitigated amount for granted and moved on. With our increase in Crits, our DPS also became more subject to randomness – not just from the Crit itself, but also whether we’d have a 25% or 50% mitigation hit 6% of the time. This effect is very strong in Mages, whose generally obscene Crit% helps to alleviate a lot of the partial resists on bosses. It can also help you to figure out whether some of the damage lost is perhaps due to this greater reliance on random chance.

This means for me, that I will focus more on Crit than before – Haste increases the number of chances for a critical hit in any timespan, but does not have any effect on the partial resists. Crit gives you a higher chance to crit, but indirectly also lowers the amount of damage you lose to partial resists. It also reveals the importance of this like Curse of Elements or Ebon Plague, which give a flat damage% modifier, which is not mitigated.

Because of its enormous reliance on chance, normal divisions and levels of deviation, the maths have to be horrendous (and I am not too good at those) – it could be I am barking at the moon with this, but then future WoL or WWS parses might reveal a pattern.

You crit for 2000 damage; 12.5% of this (25% base damage) is rested = 1750 damage done