Do we have an idea what that 'up to 1%' means?
I see multiple possibilities:
- a random number between 0 and 1
- a random number between x and 1 (alike weapon damage range)
- a simple hard cap, as in you cannot have more than 100% armor penetration

If a mob has zero Armor you can not reduce it any further.
Standard Blizz-wording.

Is there a way to get your chance to be missed from defense skill? I'm curious to know whether that increases at the same rate as dodge/parry or if it is still .04 per point.

Thank you for pointing me to your thread, I've read through the whole thread and its good to know I'm not alone on this.

About agi to dodge, tests from a friend showed that it too has deminishing effects:

+agi from gear/buffs (no def/dodge rating)	additional dodge from base (2.3220000267029 @ 115 agi)	+agi/+dodge
121	1.721002579	70.30785514
154	2.190250874	70.31158022
155	2.204469681	70.31169508
171	2.431964874	70.31351555
180	2.559926033	70.31453162
183	2.60257864	70.31487817
199	2.830053329	70.31669613
212	3.014867783	70.31817489
236	3.356044292	70.32088359
367	5.217829704	70.33575659

Nope, there isn't any API that will tell you your missed chance as far as I know.

Really? I tested this on my enhancement shaman, who has lots of agi gear, and found that it gave dodge at exactly the linear rate I would expect on live. I didn't save the numbers because the result was uninteresting, but I checked many different combinations.

I wonder if this varies depending on class?

That was also, I think, 1 build ago or maybe 2. Perhaps it's changed. I'll check again.

Well, I'm still using the char window, but here are my results, redoing the test on my enhancement shaman (Level 70, untalented, no defense or dodge rating):

Looks to me like there is some small variation, probably due to rounding, but no significant trend.

The paperdoll frame in the default UI uses num = GetDodgeBlockParryChanceFromDefense() then formats the tooltip as "Increases chance to Dodge, Block and Parry by (num). Decreases chance to be hit and critically hit by (num)". Based on how things are looking now, I think the UI is maybe lagging behind the mechanics.

I had a friend of mine(Imbamoo, Level 80 Warrior) help me do some testing on Defense, results show Dodge and Parry from Defense also have diminishing returns.

Also, the amount of Dodge and the amount of Parry given from Defense are not the same.

Defense	Dodge	Parry	+Defense	+Dodge	+Parry	+Dodge/+Defense	+Parry/+Defense
400	2.2268002033	5.0000000000
401	2.2686409950	5.0418405533	1	0.0418407917	0.0418405533	0.0418407917	0.0418405533
402	2.3104813099	5.0836806297	2	0.0836811066	0.0836806297	0.0418405533	0.0418403149
403	2.3523213863	5.1255197525	3	0.1255211830	0.1255197525	0.0418403943	0.0418399175
404	2.3941609859	5.1673579216	4	0.1673607826	0.1673579216	0.0418401957	0.0418394804
405	2.4360001087	5.2091956139	5	0.2091999054	0.2091956139	0.0418399811	0.0418391228
406	2.4778389931	5.2510328293	6	0.2510387897	0.2510328293	0.0418397983	0.0418388049
408	2.5615153313	5.3347043991	8	0.3347151279	0.3347043991	0.0418393910	0.0418380499
413	2.7706995010	5.5438699722	13	0.5438992977	0.5438699722	0.0418384075	0.0418361517
414	2.8125352859	5.5857009888	14	0.5857350826	0.5857009888	0.0418382202	0.0418357849
421	3.1053736210	5.8784971237	21	0.8785734177	0.8784971237	0.0418368294	0.0418331964
432	3.5655088425	6.3385305405	32	1.3387086391	1.3385305405	0.0418346450	0.0418290794
440	3.9001221657	6.6730446815	40	1.6733219624	1.6730446815	0.0418330491	0.0418261170
452	4.4019951820	7.1747260094	52	2.1751949787	2.1747260094	0.0418306727	0.0418216540
460	4.7365455627	7.5091204643	60	2.5097453594	2.5091204643	0.0418290893	0.0418186744

So, I'm trying to use the /dump command to get more accurate numbers, but even though I installed Chatter I can't get the copy text feature to work. I click the button, and then alt-tab to notepad and there is nothing to paste. Any idea what I'm doing wrong?

Ok, you're right--Agility does give slightly diminishing returns on dodge. Without rounding I see the trend on my shaman (again, level 70, untalented):

However, this seems pretty insignificant. After stacking 369 +agility, I've lost less than .02% dodge chance due to this effect:

369 * 0.040444319810325 = 14.923954010009925
369 * 0.040485382080075 = 14.939105987547675

The difference between multiplying by the coefficient at 369 agi and at 4 agi is 0.01515197753775

By finding the level 79 (78/77) values for 50% damage reduction and interpolating.
It was linear from 1-63 in vanilla, then 1-60 and 60-73 in BC.

So it should be linear from from ~74-83 in Wrath.


Actually, it was posted before that AC conversion hasn't changed yet.
http://elitistjerks.com/836091-post47.html

From that, a level 83 opponent means:
levelModifier = 83 + 4.5*(83-59) = 191
You get 50% damage reduction when temp == 1, i.e.
Armour = 10*(8.5*levelModifier+40) = 16635, and 15232.5 vs. level 80 mobs.


Conclusion

For 50% reduction, you need 15232.5 AC vs. level 80 mobs, 16635 AC vs. level 83 bosses.
To cap, you'd need 45697.5 AC vs. level 80 mobs, 49905 AC vs. level 83 bosses.

Doing some weapon-less Armor Penentration tests at level 70 on level 36 raptors, no sunder:

290-291 damage, Enemy Armor Reduced by up to 25.39%, actual hit: 263 damage. 9.31% damage reduction.
156-157 damage, Enemy Armor Reduced by up to 0.00%, actual hit: 138-139 damage. 11.53% damage reduction.
Difference: 23.8%

Level 68 felboars, no sunder:

290-291 damage, Enemy Armor Reduced by up to 25.39%, actual hit: 200 damage. 31.03% damage reduction.
156-157 damage, Enemy Armor Reduced by up to 0.00%, actual hit: 98-99 damage. 37.17% damage reduction.
Difference: 19.7%

Level 68 felboars, 5xsunder (2600 armor reduction):

290-291 damage, Enemy Armor Reduced by up to 25.39%, actual hit: 232 damage. 20% damage reduction.
156-157 damage, Enemy Armor Reduced by up to 0.00%, actual hit: 117 damage. 25% damage reduction.
Difference: 25%

I can't really think at the moment to figure out their exact armor and how the percent reductions work, but at least here's some data points.

It appears that against the boar, the effect of the % armor reduction is roughly the same as the live implementation (1316 armor penetration was about half as effective as the 2600 armor reduction from Sunder). No nerfs, definitely, and an increase in effectiveness on the higher armor bosses where we currently see less return from armor penetration.

So, it appears to me, based on this, that Armor Penetration rating applies after Sunders. When you reverse engineer the armor values for the sundered boars, one finds that the sundered boars have about 3600 armor, and with 25.39% ArPen they mitigate as though they have about 2650 armor; If Sunders apply first, you'd expect to see 3600 * (1-.2539) = 2685 armor; if they apply after, it would be 6200*(1-.2539) -2600 = 2025 armor. Since the former is a much better fit, it appears that ArPen applies after Sunders.

A typical raid boss at 70 has 7700 or 6200 armor; after sunders and FF, this is reduces to 4500 or 3000; thus, 1% ArPen will give either 45 or 30 reduction. Since it takes about 7.4 ArPen Rating to get 1% reduction at 70, you thus get either 6 or 4 armor reduction per point of ArPen rating. Since ArPenRating has replaced ArPen at about a 1:7 ratio, it appears to me that this is, for PvE purposes, a moderate nerf to the power of ArPen rating.

How this works out at 80, of course, depends on how much armor bosses have, which I haven't seen any numbers for yet.

Soon as I get out of raid tonite I can determine the armor value of the Dalaran boss target dummy using static bloodthirst damage. More later.

It's zero. That was my first hope of testing armor penetration effects, but it proved useless.

It seems to have about 40% armor reduction, about 10280 armor, using a very unscientific testing method. (Note that the Training Dummies in Orgrimmar definitely have zero armor. It seems the ones here in Dalaran are different.)

(edit) More test details:

Wielding a single [Dirk] with exactly 1400 AP and no armor penetration rating, my damage range is 161-163. My experienced damage range against Heroic Training Dummy with no armor debuffs active is 94-95. My experienced damage range against Heroic Training Dummy with 5-CP Expose Armor active (3925 armor reduction) is 110-112.

Let's assume that the expected damage is always the mean of the minimum and maximum of the range (not necessarily accurate, but close enough for this). Thus, my expected base damage is 162, my expected damage with full armor on the target is 94.5, and my expected damage with Expose Armor up is 111. Thus, the base reduction equals 1 - 94.5 / 162 = 41.67%, and the reduction after EA equals 1 - 111 / 162 = 31.48%.

To figure out the actual armor count we use the formula A = R * F / (1 - R), where R is the damage reduction percentage and F is the "armor factor," equal to 467.5 * Attacker Level - 22167.5, or 15232.5 for a level 80 attacker (me).

For the base reduction of 41.67%, we calculate A = 10880.36. From this value we subtract 3925 and calculate the resultant damage reduction R = A / (A + F) = 31.35%. This is just slightly off the experimentally calculated damage reduction.

Now for the reduction after EA of 31.48%, we calculate A = 6998.72. From this value we add 3925 and calculate the resultant damage reduction R = 41.76%. Again, only slightly off.

It looks like our experimentally determined values are too close together to represent reality. However, we can see that the armor values are reasonably close to one another. Most likely the actual armor amount is somewhere between 10880 and 10924.

(edit 2) 10900 seems like a very good approximation for it. The damage reduction provided by this amount of armor seems to be slightly less than what "high armor" bosses had in BC (7685 armor, or 42.13% reduction, compared to 41.71% reduction here).

(edit 3) Together with Landsoul, took a lot of different approaches and mostly ended up corroborating the estimate of 10900. This will likely be a good value to work with in theorycrafting, going forward.

Building on earlier findings, I attempted to confirm how armor penetration worked. Whacking more on the Dalaran Dummy, I dug out some of the old world penetration gear I had in my bank (it wasnt much because I DE'ed most of it) and I took some more bloodthirst data while under the effects of armor penetration and madness of the betrayer proc with the dummy fully sundered to -3925

3119 AP, 1403.55 expected BT damage
987 dealt with 7.66% penetration.
987 / 1403.55 = .7032168 applied
15232.5/.703216843 - 15232.5 = 6428.670593 armor

2987 AP, 1344.15 expected BT damage
946 dealt with 7.66% penetration.
946 / 1344.15 = .7037904996 applied
15232.5/.7037904996 - 15232.5 = 6411.014667


Now to find which methodology fits the numbers:

Penetration after sunder reduction
(10900 - 3925) * (1 - .0766) = 6441

Versus penetration before sunder reduction
10900 * (1 - .0766) - 3925 = 6140

We see it definitely seems to support that reduction is tabulated after flat reductions from things like sunder and faerie fire, etc. Concluding what Adrianna came up with in combination of mine and Vulajin's previous findings.

This means a few things.

The value of armor penetration rating goes DOWN the more armor reduction debuffs are placed on the mob. therefore, the value of armor penetration is lower in a raid setting than it is in a world setting.

The value of armor penetration is HIGHER when facing a higher armor mob versus the value of it being LOWER when facing a lower armor mob

The value of armor penetration goes DOWN the more armor penetration you stack, opposite the pre 3.0 system. (incorrect)

In my opinion, this system is counter intuitive in a sense that I predict there to be plenty of armor penetration stats on raiding gear. I would want to use armor penetration gear vs a high armor mob. I would not want to use armor penetration gear on a low armor or a debuffed mob. I would not want to stack armor penetration, because I want to follow the philosophy that it would depreciate itself if stacked versus other stats.

I believe this statement is false. The amount of armor removed (post non-rating based debuffs) is still proportional to the amount of armor penetration rating. Therefore, nothing has changed from pre-3.0 in this regard: armor penetration rating becomes better as it is stacked.

1000 armor, 93.84% damage done
900 armor, 94.42% damage done, .58% increase
800 armor, 95.01% damage done, .59% increase
700 armor, 95.60% damage done, .59% increase
600.. 96.21% ......... .61% increase
500.. 96.82% ... .61% increase
400 97.44% .62% increase

well I guess you are right, but the increasing gain is small. It's good to provoke contradictory statements.

still, the possibility to reach 0 armor on a boss is pretty much gone, it would require 740 Armor penetration rating.
7 ignore armor = 1 ArP rating => 740*7= 5180 armor penetration required pre 3.0 to reach the cap.

This is actually quite a nerf, on a 6800 armor boss you required 1950* ArP + executioner to reach the cap, now the same amount(counting that executioner is also changed to rating) would reduce armor by about 37% + 16% = 53%.
Or counting fully debuffed 6800 armor boss(which would only be sunder armor + CoR/FF now?) would have 3400 armor left before ArP comes into play, effectively removing 3400*0.53=1802 Armor removed.

So basically it's a (1950+840=2790, 2790-1802=988) a loss of 988 ArP if you are capped now before the patch, or about 35% less armor removed.

*(1950 ArP required if using Sunder armor, curse of recklessness and faeri fire, 6800-2600(SA)-800(CoR)-610(FF)-840(executioner)=1950)

Except, theres no such thing as a 6800 armor boss.

0 = 1350(pen) + 2600(SA) + 810(CoR) + 840(exec) + 600(FF) = 6200 armor boss which is the low version, the high version being 7685 or some sort 7700.

on a 6200 armor boss needs 1350+executioner (7685 / 2835+executioner) the same amount of rating would yield 1350/7/7.4038=26.05% and 2835/7/7.4038=54.70% for level 70 by your reasoning. Not sure how CoR/Faerie fire stacking works or doesn't work now..

While the numbers are odd, the conclusion still remains that ArP will no longer be a superpower stat, rather a washed down one with its value significantly reduced into oblivion. Imagine the 1350 penetration increasing your overall dps from 89% to 100% on a low armor boss now decreased to 89% to 92% something or other after the change...