MIN STATS

Here follows an explanation of the stats that you will be going after as a Death Knight such as hit rating, defence rating, dodge and parry - most of which has changed in Wrath of the Lich King (WotLK):

DPS Mechanics

Attack power(AP)

14 attack power grants 1 damage per second.

Increases damage dealt by attacks that scale with AP.

Attack power is gained by 'Attack Power' and Strength (1 strength grants 2 attack power).

Expertise Rating

At level 60, 2.5 Expertise rating = 1 Expertise
At level 70, 3.92 Expertise rating = 1 Expertise
At level 80, 8.195 Expertise rating = 1 Expertise

1 Expertise = -0.25% chance that your attacks will be dodged or parried

Expertise is useful in increasing DPS, and TPS (Threat Per Second)

Against mobs 3 levels higher and Boss(Skull) level mobs, a DPS player needs 26 Expertise to not see dodges. Tanking Death Knights need 60 Expertise (not Expertise rating) to prevent his/her attackss being parried by the boss.

Mobs can only parry from the front, thus (melee) DPS should not have a problem with parries so long as they are behind their target.

Hit Rating

Against mobs 3 levels higher than you and Boss(Skull) level mobs

Special attacks (shown in the combat log in yellow) cap at +9% to hit.
One handed weapons (in the main hand only) and two handed weapons have a 9% chance to miss.
Dual-wielding, you have an overall 28% chance to miss.
Spells cap at +17% to hit. Any damaging skill that does not scale directly with weapon damage is considered a spell for determining miss/resist.
Hit rating scales faster for spells than it does for physical abilities.

At level 60, 10 Hit rating = 1% to hit.
At level 70, 15.77 Hit rating = 1% to hit.
At level 80, 32.7 Hit rating = 1% to hit.

Our effects are considered physical skills:

At 60, 90 hit rating caps 2h/yellow attacks.
At 70, 142 Hit rating caps 2h/yellow attacks.
At 80, 294 Hit rating caps 2h/yellow attacks.

Dual-wielding takes significantly more hit rating to cap white attacks, nearing 27% hit to the cap

Critical Rating.

At level 60, 20 agility = 1% to Critically strike.
At level 70, 30.03 agility = 1% to Critically strike.
At level 80, 62.5 agility = 1% to Critically strike.

At level 60, 14 Critical Strike rating = 1% to Critically Strike.
At level 70, 22.07 Critical Strike rating = 1% to Critically Strike.
At level 80, 45.90 Critical Strike rating = 1% to Critically Strike.

Critical strike rating will applies to spell based critical strikes as well as melee critical strikes at the same ratio.

Haste Rating

At level 60, 10 Haste rating = 1% haste
At level 70, 15.7 Haste rating = 1% haste
At level 80, 32.7 Haste rating = 1% haste.

For every 1% haste you have, your attack speed increases by 1%. Haste stacks in a multiplicative manner.

Tanking Mechanics

Defense Rating

At level 60, 1.5 Defense rating = 1 Defense Skill.
At level 70, 2.36 Defense rating = 1 Defense Skill.
At level 80, 4.91 Defense Rating = 1 Defense Skill.

Defense increases Dodge and Parry (as well as block for shield-wearers) and reduces the chance to be Hit and Critically hit until the soft-cap.

At 60, Defense caps at 440 (210 rating.)
At 70, Defense caps at 490 (330-331 rating.)
At 80, Defense will cap at 540(687-688 rating)
Ratings wind up in a decimal point, so depending on how things are rounded you may need one additonal rating to achieve the defense cap on your character screen's defenses tab.

After this point - You will be uncrittable by mobs 3 levels higher than you and Boss(Skull) level mobs. The chance to be hit by mobs will not decrease further. All Defense skill after this grants dodge and parry as usual.

Dodge Rating

At 60, 12 Dodge Rating = 1% to dodge.
At 70, 18.9 Dodge rating = 1% to dodge.
At 80, 39.3 Dodge rating = 1% to dodge.

Dodge grants a flat % chance to avoid damage.

NPC's can dodge attacks from behind, players cannot dodge attacks made from behind. Ranged attacks can not be dodged, but have an inherently higher chance to miss.

Parry Rating

At 60, 15 Parry Rating = 1% to parry.
At 70, 23.65 Parry rating = 1% to parry.
At 80, 49.18 Parry rating = 1% to parry.

Death Knights increase their parry rating by 25% of their strength.

When a player parries an attack he gains a 40% haste to his current swing. However, this haste cannot reduce the current swing to less than 20% of the swings total time. When an NPC parries an attack, they also gain a haste to their current swing, causing chains of parried attacks to be fatal in some situations for players (this is why expertise is good for tanks).

For example: Bob the Death Knight's swing timer is 3.3 after factoring what haste he has. Bob´s swing timer has just reset, and he parries his opponent's attack, giving him a 40% haste for the next swing - dropping the time till his next swing from 3.3 to 1.95. If Bob´s swing timer was already at 1.0 and he parries an attack, his next swing would come in 0.66 of a second(the 20% minimum) not 0.6 sec.

NPC's and players cannot parry attacks made from behind them.

Resistance

Resistance increases your chance to completely or partially avoid spell or spell-based attacks. A good example of a spell-based attack is an elemental's standard attack, which only deals elemental damage based off the flavor of elemental.

Resistance (like armor) hard caps at 75%. Any resistance after acheiving 75% resistance in a school is useless in a pve setting, unless you're dealing with mobs who lower resistances.

Against a level 63 mob, 315 resistance will grant 75% average resistance.
Against a level 73 mob, 365 resistance will grant 75% average resistance.
Against a level 83 mob, 415 resistance will grant 75% average resistance.

The easiest way to determine the resistance cap is to multiply your enemy's level by 5.

Having a 75% average resistance grants you a 75% chance to negate effects that come coupled with a non-damage component spell coupled with snares, like frost shock, or utility spells like polymorph that are incapable of a partial effect - they hit or they miss.

Spells that are not coupled with a secondary non damage effect work differently. At the resistance cap, you will often see spells get total resists (no damage), frequently resist 75% of their intended effect, slightly less frequently, you'll see spells deal half damage, occasionally resist 25% and very few full damage from spells of that school.

Threat

Threat is a measure which determines what an NPC attacks.

To gain threat, players in melee range need to pass the current target's threat by 10%. Ranged players need to pass the current target's threat by 30%

PVP Mechanics

Resilience

At Level 60, 25 Resilience Rating = 1% Resilience
At Level 70, 39.4 Resilience Rating = 1% Resilience
At Level 80, 81.9 Resilience Rating = 1% Resilience

1% Resilience grants

Reduces the chance to be critically struck by 1%.
Reduces the damage taken by critical strikes by 2%.
Reduces damage take by damage over time effects by 1%.
Reduces Mana Drain and Burn effects by 2%.

Skills that are activated by being crit takes your base chance to avoid critical strikes into account and have a chance to activate even though an attack from an enemy player did not crit.