Stats and Caps

One of the most important things in understanding what gear you need to get is understanding the what stats you need, and how much of each. This post will attempt to explain the stats as they apply to everyone.

The following flowchart explains how the combat system in WoLK determines how much damage is done:


Note, block/parry/dodge changed for cataclysm:
- blocked attack = 30% less damage taken => mitigation
- parried attack = 50% less damage taken on that attack and 50% less damage taken on the next attack => mitigation
- dodged attack = no damage taken on the dodged attack => avoidance

Stats influencing how much damage follows which path in the chart are as follows

Crittability
This is the change of an attack to be a critical strike and thus do double damage. Note that this is determined as a percentage of overal attacks, so it's possible for a crit to miss/be dodged/parried/blocked/resisted.

Tanks have talents that reduce this to by 6%, which is enough to be uncrittable by a raid boss (or any other mob at most 3 levels above you)

Hit
is the stat you need to make sure none of your attacks miss.

Specific values are:
- yellow/special (melee) attacks have an 8% miss chance
- dual wield melee attacks have a 27% miss chance versus raid bosses (88) and a 24.4% miss chance versus HC bosses (87)
- single-wield and 2handed melee attacks have a 8.2% miss chance versus raid bossses (83), and a 5.4% miss chance versus HC bosses (82)
- Magical attacks have a 17% miss chance versus raid bosses (83), and a 6% miss chance versus HC bosess (82)

keep in mind that having a dranei in you party effectively lowers the chance to mis by 1% due to their 'Heroic Presence'
also note that while spell hit and melee hit are bot based on hitrating, both have a different conversion ratio

for (single-wield) melee the hitcap is 961 hit rating at level 85 (841 if you're a Draenei due to your racial)

Expertise
is the stat you need to prevent your attacks being dodged (soft cap) and parried (hard cap).

raid level bosses have a 6.5% chance to dodge, 26 expertise negates this (this is 781 expertise rating at level 85)
raid level bosses have a 12-15% chance to parry, 60 expertise negates this (this is 1682 expertise reating at level 85)

A parry increases the speed of the next attack by 40%, for this reason attacks getting parried increase the amount of damage the mob you're attacking deals
out.

NOTE for DPS: if you always make sure you're attacking from the side/back of the mob you only need to worry about the dodge cap

Armor
Armor decreases the amount of physical damage you take by a certain percentage.
The maximum decrease amount is 75% and requires 49,905 armor at level 80

The counter to armor is 'Armor Penetration' which reduces your target's armor by a certain percentage. Lot's of mobs have armor, so for a melee DPS stacking armor penetration is a good idea.

Resistance
is basically armor versus magical damage. There's 5 different kind of magical attacks (arcane, fire, frost, nature, and shadow) each of witch has it's own resistance value associated with it.

Effect of resistance is depend on the kind of spell:
- binary spells either take effect or not
- non-binary spells(mostly DOTs) have their damage reduced by a certain percentage (exactly the effect armor has on physical attakcs)

415 is the resistance cap (anything more has no effect) and will lower the amount of damage/chance to be affected by 75%.
actual % of damage resisted = (75 * resistance) / (caster level * 5)

The counter to resistance is 'spell penetration', and 1 point in spell penetration negates 1 point in resistance. Note: Spell penetration is essentially useless in PvE as mobs with any significant resistance values are basically non-existant.

I'd like to give some information about spell hit, which is different then melee hit, which Baridin also covered in the post above.

Spell hit is a combat attribute that increases a caster's chance to hit with spells. Spell hit is primarily obtained from talents or gear that has hit rating. The more gear with hit rating a caster has the lower the chance the caster's spells will miss.

Increasing spell hit

Chance to hit can be increased by talents or gear up to 100%. Hit rating is a stat found on gear that increases hit chance by a certain percent per point, based on level. At level 70, 12.615 hit rating is equivalent to 1% hit. At level 80, 26.232 hit rating is equivalent to 1% hit.

At level 80, the highest level mob currently present is level 83 (e.g. all WotLK raid bosses), a level 80 caster has an effective spell hit rating cap of 446. That assumes no other spell hit sources.

Aside from gear with spell hit rating, chance to hit can also be increased through some buffs and spells. Draenei casters give an additional 1% hit to their group with Inspiring Presence, as well as debuffs like a balance druid's Improved Faerie Fire and a shadow priest's Misery. The following table lists some talents that also increase a caster's chance to hit with spells. Taking these effects into consideration lowers the effective hit rating cap.

Talents and gear combined, chance to hit with spells can reach 100%. Casters should keep this cap in mind when considering their gear. For PvE raiding, bosses are considered to be 3 levels higher than the caster, meaning that +17% is the most that will be effective. For PvP, anything more than +4% chance to hit is typically excessive. Note that some classes (for example Paladins and Rogues) can spec to gain extra chance to have spells miss them. Also, some abilities (e.g. - Cloak of Shadows, and spell resistance for binary spells) give the player using the ability extra chance to have spells miss as well. Extra spell hit does in fact mitigate this extra chance to miss, but is otherwise useless.

For example, as I'm a Draenei Shaman and elemental specced, I need 342 hit rating to never miss a lvl 83 raid boss. I have 1% hit from my racial and 3% from one of my talents. Many other classes have similar +hit talents in their spec, so never forget those when you're calculating your hit chance.

Maybe some of the text you read looks familiar, that's because it's mostly a copy and past from wiki
So if you want to read the whole article, go here: http://www.wowwiki.com/Spell_hit

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bump as I've added armor, armor penetration, spell penatration and the flowchart