We all know how to quantify the DPS trinket procs: normalize proc strength over expected uptime, and voila! you got a passive stat equivalent. However, I have never seen any model for quantifying tanking trinket procs.
Well, today on forums.worldofwarcraft.com I accidentally stumbled into an argument about trinkets; and being challenged on my casual statement that the Glyph of Indomitability on-use bonus is better than the Black Heart proc, I came up with a quantification technique to show exactly why that is so (which point seemed rather obvious to me, so I never bothered formalizing it before).
I would now like to propose that model -- and if anyone had done similar work before, please do not hesitate to point it out to me; I have not been able to find anything of the sort. I will keep using the Black Heart proc and Glyph on-use, simply because I think it makes for a very instructive (and apparently unexpected to most) comparison, and serves as a rather simple illustration of my model.
To start with, I think it rather obvious that unlike DPS trinkets, tanking trinkets' procs and uses are expected to kick in at the "oh crap!" moment. As such, you don't want to spam it on CD -- you want to fire it off in the "tank killer" situation.
What constitutes a tank killer? A common situation is when the tank must eat a sequence of strong attacks, while not getting healed, or getting insufficiently healed, due to fight mechanics (not getting healed due to healer incompetence should not be considered). An example I saw recently was Soul Reaper on LK: it fired off right after an unlucky Defile merged with the previous one, separating the healer from the tank by more than 40 yards. In such a situation the tank had to do what they can to survive the flurry of attacks while the healer, being a shaman with no "run through defile safely" CDs, had to go around it.
So the basic concept here is a flurry -- a tank must be able to survive a flurry of attacks, by avoiding/mitigating some percentage of the incoming damage. This is the time to blow your trinket's on-use, or to pray/hope/meditate that your trinket has procced at the right time. The shortest possible flurry is 2 attacks (since decent tanks never get one-shotted except through someone's gross incompetence, e.g. dying inside Frostmourne, which also should not be considered here).
So, how do the Glyph's on-use, and the Heart's proc, contribute to the tank being able to survive, say, a 2-hit flurry without getting gibbed? In the above Soul Reaper scenario, it's actually a 4-hit flurry occurring in a 2-hit time period, but let's keep it simple). We will first consider the basic two-attack flurry case.
A typical decently geared tank will have around 60% avoidance, or 40% in ICC. Let us say that any meaningful avoidance or mitigation on the flurry will permit tank survival -- i.e. that the extra armor from the Heart is as good as 100% damage reduction in terms of letting the tank survive until the next heal.
Then the basic chance to dodge/parry at least one attack from the 2-hit flurry, without either trinket, is: 1 - 0.6^2 = 0.64. (0.6^2 being the chance that both blows connect).
Now let's factor in the Glyph. At such gear level it will give you about additional 6% dodge; so the chance of avoiding at least one attack becomes: 1 - 0.54^2 = 0.71: a 7% improvement over the baseline case. Normalizing, your chance to die has been cut from 36% to 29%, or by 20%.
Now let us instead consider the Heart. it has 17% uptime. We will set aside for now the rather more complicated question of whether its proc will be up for the entire duration of the flurry. If the proc is up, let's assume that survival is guaranteed regardless of avoidance; if it's down, it's back to the baseline survival chance. SO the survival chance with the Heart proc becomes: 0.83 * 0.64 + 0.17 = 0.70, a 6% improvement over the baseline case; about 1% weaker than the Glyph's Dodge ability. Normalizing, your chance to die has been cut from 36% to 30%, or by 17%.
Now let us instead consider the Soul Reaper case, where 4 attacks will occur in the duration of 2, in addition to the Shadow damage. If you have to dodge at least one of the four attacks (which for the Glyph is now nominally close to about 25% DR bonus you get from the Heart proc), then the value of the Glyph on-use becomes: 1 - 0.54^4 = 0.915 -- compared to the baseline survival chance of 1 - 0.6^4 = 0.83, a nominal increase of 8.5%. Normalizing, your chance to get insta-gibbed has been cut from 17% to 8.5%, a whopping 50% improvement.
The value of the Heart would remain unchanged, or even go down as flurries increase in duration, because it's gonna get less and less likely that the proc will be up for the entire duration of the flurry. In fact, with Soul Reaper, the chance of the Heart proc being up for the entire 5-second duration is a measly 8.3%.
So this is how I propose we can quantify various tanking trinket procs and on-use abilities -- by determining how they will affect a typical tank's survival probability in a representative tank-killer situation. The quantitative value of the proc becomes the improvement in survival chances under such a baseline scenario. If nobody has proposed such a model before, I would like to call it TSB -- Tank-killer Survival Bonus model.Not surprisingly to me, but apparently surprisingly to many others, the absolutely random chance of the Heart proc basically kills the advantage of the proc itself. Armor is great, but godly armor at random times is much less useful -- dodge is far less reliable than armor, but dodge on demand, because it applies to every attack individually rather than to all attacks as a group, is more reliable than a flat armor proc chance, as the value of dodge will very rapidly improve with the increase in the flurry duration. Even for the basic 2-blow flurry the Glyph controllable dodge bonus offers a slightly better survival chance than the Heart randomly times armor bonus.
Yet to be modeled is the value of the "on hits which take you below 35%"-type procs, like CTC. My sense is that while CTC's passive bonus is crap, its proc is absolutely godly -- with half-way competent healers, that proc, with its tiny 30-second ICD and 10-second duration, should be up for every single tank-killer situation on many, perhaps most, fights. That proc is nearly as good as Will of the Necropolis talent. It will give you more damage reduction , but only against physical damage (no big deal) and on 30-second ICD (not very pleasant) with 10-second duration (excellent). Again, in Soul Reaper scenario, with competent healers the CTC proc should be available for every single Soul Reaper, thus being nearly as good as passive 5.7k of armor -- because of course the time when you need that extra armor is when the tank gets hit the hardest, during the light-hitting times the extra armor would mostly serve to make overhealing even higher.
It would also be nice if someone more comfortable with the EHP model would more precisely quantify the effect on the proc on the tank-killer survival, as in the above example I basically used back-of-the-envelope math; but the basic idea -- quantifying the proc value as the improvement in the chances to survive a tank-killing flurry of attacks -- should be sound.
Thoughts? criticisms? rotten tomatoes?