This is a quick "Beginner Theorycraft" article to explain the basics of the Attack Table to new players. Most of the basic defensive examples were "borrowed" from Winchester's guide, but I've tweaked a few numbers and added a significant amount of commentary. I've also added a large section on the offensive side of things, so that we have a place to point new players who want to know why hit/expertise are good threat stats for them.

This is designed to be a "tutorial," which means "readable by someone who's just getting their feet wet in tanking theory." It's debatable whether this should be in Basic Training or Advanced Training, but since it matches the level of Winchester's guide I chose to go with Basic Training.

Any comments/questions/suggestions are welcome, especially those that further enhance the readability of the guide and the quality of information it contains.  Comments can be posted in this thread.

The Attack Table Of Contents

• The Attack Table - Basics
• The Attack Table on Offense
  • One-Roll Mechanics
  • Two-Roll Mechanics
• Offensive Abilities
• Rating Conversions and Caps
• Appendix: Crushing Blows
• Sources
• Changelog

The Attack Table - Basics

To understand some of the gearing choices a paladin has to make, we first need to understand how WoW resolves combat events. The fundamental mechanic is something called the Attack Table.

Every time a player or boss attempts to make an attack, the game rolls to determine whether the attack succeeds or fails. The Attack Table is the scale which determines the results. To illustrate this, let's look at a few simple examples. First, let's consider a lvl 80 mob attacking a lvl 80 paladin with 400 defense and base avoidance (5% miss, 5% dodge/parry, 10% block) plus talents (5% dodge/parry from Anticipation and Deflection). The attack table is then constructed like this:

00.01-05.00 = miss
05.01-15.00 = dodge
15.01-25.00 = parry
25.01-35.00 = block (100% damage - block value)
35.01-40.00 = crit (200% damage)
40.01-100.0 = hit (100% damage)

the server then does a /roll 100 to determine the outcome (though it does this to more decimal places than a standard /roll 100). If it rolls a 12, you dodge; a 26 is a blocked hit; a 36 is a critical strike, and anything over 40 is a regular hit.

If instead we're considering a lvl 83 boss attacking a lvl 80 paladin, we have to make a few modifications. For each level above 80, the boss gains 5 weapon skill, granting him an additional 0.2% chance to crit and reducing the chance for his target to avoid or block an attack by 0.2%. Thus, we've now got a 5.6% chance to be crit, and our chance to dodge, parry, block, and miss are now 9.4%, 9.4%, 9.4% and 4.4% respectively:

00.01-04.40 = miss  (4.4%)
04.41-13.80 = dodge (9.4%)
13.81-23.20 = parry (9.4%)
23.21-32.60 = block (9.4%)
32.61-38.20 = crit  (5.6%)
38.21-100.0 = hit   (62.8%)

Before moving forward, let's briefly discuss how the table is arranged. As you see, avoidance is at the very top of the table, followed by block, followed by crits, followed by regular hits (which fill up whatever remains of the attack table). Note that blocks and crits/hits are separate entries on the table - this means that you can never block a crit, for example.

As you increase the chance to do any one of these things, it "pushes" the things below it further down on the combat table. As an example, if we add 10% block, it will "push" crit and hit further down, and as a result 10% of the hit chance will be "pushed" off of the end of the combat table. The net result will be that we'll still have a 5.6% chance to be crit, but the chance to block will be up to 19.4% and the chance to be hit will drop to 52.8%:

00.01-04.40 = miss  (4.4%)
04.41-13.80 = dodge (9.4%)
13.81-23.20 = parry (9.4%)
23.21-42.60 = block (19.4%)
42.61-48.20 = crit  (5.6%)
48.21-100.0 = hit   (52.8%)

As tanks, we want to take as little damage as possible, which means we want to reduce the chance to be hit or crit as much as we can. However, since crits cause large, spiky damage that's harder to heal through (and more likely to kill us), we usually make removing crits from the table our first priority. There are two possible ways to accomplish this:

1. From the example above, it should be clear that if we increase our avoidance or block enough, we can push hits and crits off of the combat table. Since block is more efficient at doing this (see BT101: Combat Ratings), the fastest way would be to somehow come up with another 68.4% block from gear. Holy Shield gives us 30% towards this, but the other 38.4% is still a lot of block to have to come up with. In addition, if Holy Shield expires or gets used up, we're suddenly able to be crit again, which is undesireable.
2. The more convenient way to remove crits from the table is through defense skill. Each point of defense skill increases the chance to miss/dodge/parry/block by 0.04% (before diminishing returns, which we'll ignore for this tutorial) and decreases our chance to be crit by 0.04%. Thus, we need 140 additional defense skill (for a total of 540) to reduce our chance to be crit by 5.6%.

To reach 540 Defense, we need 689 defense rating, which should be every tank's first gear priority upon hitting lvl 80. By doing so, we gain a good chunk of avoidance, and more importantly reduce the chance to be crit to zero, removing it from the combat table entirely:

00.01-10.00 = miss  (10.0%)
10.01-25.00 = dodge (15.0%)
25.01-40.00 = parry (15.0%)
40.01-55.00 = block (15.0%)
----------- = crit  (0.0%)
55.01-100.0 = hit   (45.0%)

Now that we can't be crit, our aim is to reduce that 45% chance to be hit by pushing as much of it off of the table as possible. There are a few schools of thought on how to do this most effectively.

• Stacking block rating is the most efficient way to get rid of hit, since it's unaffected by diminishing returns and has a favorable rating->% conversion. On the other hand, you still take damage when you block a hit (just less than you would a regular hit). In some cases this is fine (large block value and weak incoming attacks), but as the incoming attack size increases relative to block value, it becomes less effective. Some people still like to maintain this "unhittable" status, however. You may also see people refer to this as "uncrushable," which is an outdated term referring to pre-Wrath when Crushing Blows were still part of the attack table for bosses.
• Stacking avoidance also removes hit, though at a slower rate because the conversions are less favorable and subject to diminishing returns. However, stacking avoidance means you'll replace those hits with avoids, so you're replacing a result where you'd take damage with one where you take zero damage.

Also, since we're paladins, we have the option of keeping Holy Shield up, which gives us a flat 30% block chance. If we consider the attack table above with Holy Shield added in as well as an additional 5% dodge/parry/block from gear, we get:

00.01-10.00 = miss  (10.0%)
10.01-30.00 = dodge (20.0%)
30.01-50.00 = parry (20.0%)
50.01-100.0 = block (50.0%)
----------- = crit  (0.0%)
----------- = hit   (0.0%)

At this point, we've pushed hit completely off the table. We now have a 50% chance to avoid the attack entirely (miss/dodge/parry), and a 50% chance to block the attack, reducing the damage we take from it by our block value. This is what we'd call "unhittable." This occurs when your combined miss, dodge, parry, and block percentages add up to 102.4% (100% plus the 0.6% reduction to miss, dodge, parry, and block due to the boss's 3-level advantage).

It's also worth noting at this point that some special abilities that bosses use ignore sections of the table (for example, can't be dodged or parried). In those cases, you may find that the ability can hit even if you're "unhittable" to regular melee attacks.

Given the nature of the combat table, it's theoretically possible to push block off of the table by stacking more pure avoidance. Practically, this isn't possible because the gear to accomplish this doesn't (and won't, for encounter balance reasons) exist.

This tutorial has focused solely on incoming attacks from bosses, but the attack table system is also used for our offensive attacks. We'll discuss that in the next section.

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The Attack Table on Offense

Our melee attacks use a very similar attack table system that a boss's attacks do. However, our spells and special abilities (as of patch 3.0 anyway) use a slightly modified version of the attack table mechanic. A convenient way to describe the difference is by using the number of /rolls required to get a result; our melee attacks on a boss (as well as the boss's attacks on us) use a "one-roll" system, which is what's described in the previous section. Our spells and special abilities use a "two-roll" system (as discovered in April by testers at EJ [1][2]), which I'll describe in more detail later in this tutorial.

First, let's look at our auto-attacks and the "one-roll" system:

One-Roll Mechanics
The one-roll system only requires one roll to calculate the result of an attack. It treats avoids, crits and hits as separate entries on the attack table. Against a lvl 83 raid boss with no combat rating adjustments (i.e. 0 hit rating or expertise), our attacks have a 14% chance to be parried, 6.5% chance to be dodged, and 8% chance to miss. In addition, a lvl 83 boss has an inherent "melee crit suppression" of 4.8% (3% from the difference between your weapon skill and the boss' defense skill, and 1.8% from the level difference[3]), and against auto-attacks a "glancing blow" chance of 24% [4] (glancing blows do 75% damage to a raid boss). If we assume we have a 24.8% total chance to crit (to make the numbers easy), the attack table is constructed as follows:

00.01-08.00 = miss  (8%)
08.01-14.50 = dodge (6.5%)
14.51-28.50 = parry (14%)
28.51-52.50 = glancing (24%)
52.51-72.50 = crit  (20%)
72.51-100.0 = hit   (27.5%)

The server does a /roll 100 for each auto-attack to determine the outcome. As you can see, we actually have a 28.5% chance to miss our attack entirely. This is where combat ratings come in. Through hit rating and expertise, we can reduce the chances for misses, dodges, and parries to make sure our attacks connect.

It takes 32.79 hit rating to achieve 1% bonus melee hit. By stacking 263 hit rating, we gain 8.02% hit and remove miss from the attack table.

Similarly, it takes 8.197 expertise rating for one expertise skill, which reduces dodges and parries by 0.25%. This conveniently works out to 32.79 expertise rating for 1% dodge and parry suppression (4 expertise skill). This means that we need 26 expertise skill (214 rating) to remove dodges from the table, and 56 (460 rating) expertise skill to remove parries from the table. Since expertise is only half as effective after 26 rating, and few of our abilities depend on it, it's not efficient to try and increase threat by pursuing extra expertise past the 26 rating "soft-cap" where dodges are removed from the table. However, recent research has shown that expertise also provides a significant damage-reduction benefit by removing parries from the boss's attack table [5], which could be a worth considering.

There's no way to remove glancing blows from the table, but since they only affect our auto-attacks and they still do damage (and thus proc seals), this is of little concern to us as tanks. It's a greater concern to melee dps because of its position on the attack table - it's possible to stack enough crit that regular hits are pushed off of the table. At this point, extra crit does nothing for melee auto-attacks until the player further reduces their chance to be dodged/missed (attacks from behind can't be parried).

Now that we've seen how the one-roll system works, let's look at the two-roll system. The two-roll system holds slightly greater importance since it determines how the bulk of our core abilities work.

Two-Roll Mechanics
The two-roll system requires two rolls to calculate the result of an attack. The first roll is performed on an attack table that solely determines whether the attack succeeds or fails (i.e hit or miss). The second roll determines whether a successful attack will be a regular hit or a critical strike. This is most easily demonstrated with an example. Let's look at a generic special ability that acts like a melee attack, again without any combat rating adjustments. The first attack table would look like this:

00.01-08.00 = miss  (8%)
08.01-14.50 = dodge (6.5%)
14.51-28.50 = parry (14%)
28.51-100.0 = hit   (71.5%)

The game would roll on this table first to determine whether the attack hits or is avoided. If it connects (71.5% chance), the game will perform another roll to determine whether it's a hit or a critical strike:

00.01-20.00 = crit (20%)
20.01-100.0 = hit  (80%)

Since a missed attack can never crit, this has an important fundamental implication on our overall critical strike chance. Statistically, our expected critical strike is reduced due to missed attacks. If our character sheet critical strike % is 24.8% (or 20% after suppression), we only expect to see (1-(miss+dodge+parry)/100)*20% = (1-0.285)*20% = 14.3% in our recount logs. That's a pretty noticeable reduction, and one of the major reasons that hit and expertise are valuable threat stats (especially for dps classes/specs). By reducing our chance to be missed, dodged, or parried, we make better use of our critical strike chance.

The other reason (and more important reason for us as tanks) that hit and expertise are important is that for an attack to proc a seal, it has to connect. Thus every miss, dodge, and parry we see is one fewer seal proc.

As an example, let's take Judgement. Judgement works like a special melee attack that cannot be dodged or parried. Thus, the first attack table for Judgement looks like:

00.01-08.00 = miss (8%)
08.01-100.0 = hit  (92%)

This is one of the reasons that hit is better for us than expertise - several of our attacks cannot be dodged or parried, but can be missed. Shield of Righteousness is another ability that acts this way.

Spells work exactly the same way, except that they can never be dodged or parried. In addition, the spell hit cap is 17% for a raid boss rather than 8%, though the conversion from hit rating to spell hit % is more forgiving at 26.23 rating for each 1% hit. The main reason that this is important to us is that our taunts are treated as spells, and thus have a base 17% chance to miss. The attack table for a spell or taunt thus looks like this:

00.01-17.00 = miss (aka resist) (17%)
17.01-100.0 = hit  (83%)

It would take 446 hit rating to completely remove spell misses from the attack table, but since Holy Shield and Consecration are our only other abilities that uses the spell hit table, it's not worth considering the spell hit cap as a gearing priority. With the glyph that reduces our taunt hit chance by 8%, it only takes 237 hit rating to cap taunts, which makes it a valuable glyph for encounters where taunt resists are undesireable.

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Offensive Abilities
Offensive abilities have different miss rates depending on the type of ability and target level. A boss is always considered level player+3, or 83 for a lvl 80 player. Here are the melee and spell miss chances for different level targets (assuming max weapon skill):

    Target        Miss %         Dodge%   Parry%   Glancing%
    Level     Melee     Spell
     80        5.0        4        5.0      5.0        6**
     81        5.5*       5*       5.5      5.5       12**
     82        6.0*       6*       6.0      6.0       18**
     83        8.0       17        6.5     14.0       24

*  confirmed by multiple classes
** confirmed by rogues


Here's a complete list of our abilities, sorted by the type of attack table and avoidance they're subject to on a lvl 83 raid boss [9]:

Melee Abilities - 8% miss chance, 6.5% dodge, 14% parry

One-Roll:
Auto-attacks
Seal of Vengeance/Righteousness procs (cannot be dodged/parried or miss)
Holy Vengeance applications (aka SoV DoT stacks, not the DoT damage itself).

Two-Roll:
Seal of Command procs
Judgement (cannot be dodged/parried)
Shield of Righteousness
Hammer of the Righteous (it can be dodged and "deflected" because of it's ranged cleave component).

Ranged Abilities - 8% miss chance, cannot be dodged/parried, should not proc seals [6][7]

Two-Roll:
Hammer of Wrath
Avenger's Shield

Spell-like Abilities - 17% miss chance, cannot be dodged or parried, 1.5x damage on crits

One-Roll (can't crit):
Holy Shield
Consecration
Holy Vengeance (aka SoV DoT) (can't miss)
Righteous Defense [10]

Two-Roll:
Exorcism
Hand of Reckoning [10]

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Rating Conversions and Caps

Uncrittable, the artist formerly known as "defense cap":
It takes 140 defense skill from gear (for a total of 540 defense on your character sheet) to remove crits from the attack table (on defense). This is 689 defense rating from gear.

• Note that defense rating truncates, in that defense rating that doesn't bump you up to a new value of defense skill is "wasted". In other words, you get no avoidance benefit by going from 689 to 690 defense rating, whereas you do see a benefit going from 688 to 689.

Unhittable (aka "Block Cap"):
It takes 102.4% total avoidance + block on your character sheet to remove hits from the attack table (on defense).

Hit:
It takes 32.79 hit rating to achieve 1% bonus melee hit.
It takes 26.23 hit rating to achieve 1% bonus spell hit.

By stacking 263 hit rating, we gain 8.02% melee hit and remove miss from the attack table.
By stacking 446 hit rating, we gain 17.00% spell hit and remove spell misses from the attack table.
By stacking 237 hit rating, we gain 9.04% spell hit, which combined with the Righteous Defense glyph makes our taunts unresistable. [10]

Expertise
It takes 8.197 expertise rating for one expertise skill, which reduces dodges and parries by 0.25%. This conveniently works out to 32.79 expertise rating for 1% dodge and parry suppression (4 expertise skill).

• Note that expertise skill does not truncate (unlike defense), despite not showing decimals on the character sheet. Thus, every point of expertise rating gives you a benefit, even if you're only going from 10 to 10.1 expertise skill.

The expertise caps are:
"soft-cap": 26 expertise skill (214 rating) removes dodges from the table
"hard-cap": 56 expertise skill (460 rating) removes parries from the table

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Appendix: Crushing Blows

A crushing blow is an auto-attack that hits for 150% damage. It can only occur when an NPC attacks a player, and only if the NPC's weapon skill is 20 points greater than the player's current defense skill, capped at the level-maximum (400).

In practice, this means a crushing blow will only occur when tanking a mob that's 4 levels higher than you, making it irrelevant for end-game tanking in WotLK. However, evidence has shown that while under the effects of Thorim's Unbalancing Strike (which reduces total defense skill below the level-maximum of 400), his arena trash mobs can inflict crushing blows on players[8].

Crushing blows were a larger concern in the Burning Crusade, when a boss-level mob was able to crush a player (the differential was 10 points at that time). One of the selling points of a paladin tank in this era was that due to Holy Shield and the block mechanic, we were able to consistently push Crushing Blows off of the attack table.

A level 84 mob has a 15% chance to score a crushing blow on a lvl 80 player with 400 defense skill.

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Sources

[1] http://elitistjerks.com/f76/t37843-retribution_paladin_thread_wrath_3_0_a/p129/
[2] http://www.wowwiki.com/Attack_table#Melee_special_attacks_by_players
[3] http://roguerogue.com/2009/04/30/elitis ... ate-guide/
[4] http://www.wowwiki.com/Glancing_blow#Glancing_Blow_chance
[5] http://maintankadin.failsafedesign.com/viewtopic.php?f=6&t=25611
[6] http://www.wowwiki.com/Attack_table#Ranged_Attacks
[7] http://www.wowwiki.com/Critical_strike
[8] http://www.tankspot.com/forums/f63/40759-crushing-blows.html
[9] http://elitistjerks.com/f76/t37172-protection_paladin_field_manual_wow_3_0_wotlk/p12/#post1035415
[9] http://www.tankspot.com/forums/f14/50984-taunt-mechanics-guide-discussion.html
[10] http://www.tankspot.com/forums/f14/50984-taunt-mechanics-guide-discussion.html
[11]http://maintankadin.failsafedesign.com/forum/index.php?p=543112&rb_v=viewtopic#p543112

I'd also like to thank Winchester, whose basic write-up on the Attack Table provided a good foundation around which I could write the first section.

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Changelog

11/12/2009 - Added miss chance table to Offensive Abilities section
11/5/2009 - Version 1.0


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