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Attributes are the basic building blocks for a character's combat ability. The five primary attributes are strength, agility, stamina, intellect, and spirit. These five attributes along with armor appear on the character sheet under "Base Stats". These are often referred to as simply stats.
A number of secondary attributes affect specific areas of combat more directly, and are often influenced in some way by a primary attribute. Secondary attributes include critical strike rate, damage absorption, attack power, spell power, and many others.
All characters inherently have some amount of each attribute that increases with level depending mainly on class. For example, a mage will have more base intellect than a rogue, who will have more base agility. Increasing these attributes is mainly done with equipment, as well as temporary effects such as buffs, elixirs, scrolls, auras, and many other means.
Nearly all combat mechanics rely in some way on one or more character attributes. Increasing the appropriate attribute will increase damage done, reduce damage taken, increase healing done, affect a character's mana or health, or other benefits. Understanding how these attributes work is important for effective combat.
AddOns such as RatingBuster[1] can show you the actual improvements in game to your Secondary attributes which are more directly applied to combat mechanics.
Hunters gain 1 melee attack power per point of agility.
Increases chance to score a critical hit with a weapon.
Increases chance to dodge attacks. This is dependent on both class and level, in fact death knights, paladins and warriors don't.
Agility Equivalence Points is a notable formula for calculating the contribution of agility. It might be outdated with regard to hunters.
Stamina
Stamina (often abbreviated STA) has the following effects:
Stamina provides 1 health per stamina for the first 20 points of stamina, and 14 health per point of stamina thereafter.
Stamina also increases the health of a player's pet for classes with pets, although not from the player's base stamina (the stamina the player has without any armor or talent bonuses). They gain between 3 and 11 health per point of stamina, depending on the pet's type and the master's talents (see the hunter pet, minion and Risen Ghoul articles for details). There are other non-standard adjustments that can be made for stamina:
Stamina is one of the key attributes of tanks (dodge, parry, and block also being very important). It is useful to every class in PvP. Non-tank PvE characters should not actively seek out stamina, but some of it is found on nearly any piece of gear.
Intellect (often abbreviated as INT) has the following effects:
Increases spell power by 1 per point at level 80 or above. Intellect is now the main source of spell power for most cases.
Increases mana pool. Each point of intellect gives player characters 15 mana points (except from the first 20 points of Intellect that provide 1 mana for each point instead). Warlock minions gain 1 mana per point of base intellect, imps gain ~4.9 mana for each additional point of intellect, while all other minions gain ~11.5 mana for each additional point of intellect.
Increases chance to score a spell critical strike. This increase varies by class and level; in general, the relationship is linear as intellect increases. The rate of increase is generally based on the amount of intellect a class is expected to have at a certain level, given by the following table.[2][3][4]
Mastery is a unique attribute that that has different effects depending on class and specialization.
Others
Secondary attributes are player stats that affect combat directly. The four primary attributes only indirectly affect combat, by contributing to these attributes.
Physical combat
Weapon damage - Weapon damage is a property of the player's equipped weapon. Melee weapon damage is increased by enchants and sharpening stones. Ranged damage is increased with scopes.
Weapon speed - Weapon speed is a property of the player's equipped weapon and determines the time between attacks with that weapon.
Attack power - (Abbreviated as AP) Increases damage of an equipped weapon. Attack power is increased directly by gear and buffs with the attack power stat, and indirectly by strength and agility (only for hunters, rogues, shamans, and cat-form druids).
Ranged attack power - (Abbreviated as RAP) Increases damage of an equipped bow, crossbow or gun, but not wands. Ranged attack power is increased similarly to melee attack power.
Hit - Increases chance to hit with melee weapons by a percentage. Hit chance is increased by hit rating, a combat rating.
Haste - Decreases the time between attacks. This effectively increases weapon speed, but has no effect on cooldowns. Haste is increased directly by haste rating, a combat rating.
Expertise - Reduces the enemy's chance to dodge/parry by .25% per point of expertise.
Spell combat
Spell hit - Increases the chance spells will hit their target. Spell hit is increased by the same hit rating used for melee hit, but the effects differ after that point.
Spell crit chance - Percentage of spells that will result in a spell critical strike. Spell crit chance is increased by critical strike rating and intellect.
Casting speed - The rate at which spells can be cast. Increased by haste rating. Can lower the global cooldown in cases where spells are cast fast enough to be limited by it.
Defense
Dodge - Chance to dodge incoming melee attacks. Ranged attacks cannot be dodged. Dodge is increased by dodge rating and agility. Only tanks should use gear with dodge rating.
Parry - Chance to parry melee attacks with a melee weapon. Ranged attacks cannot be parried. Parry is increased by parry rating and strength. Only (non-druid) tanks should use gear with parry rating.
Block - Chance to block melee and ranged attacks with a shield. Warrior and paladin tanks receive additional block chance through their respective mastery and abilities such as Shield Block.
Armor - Decreases physical damage received. Increases your pet's Armor. Armor is always present on equippable items, such as chest pieces and shields. Shields and plate items generally have the most armor, while cloth items have the least. The base armor of an item is determined directly by its type (cloth, leather, mail or plate), item level and slot (chest, head, legs, etc). Some items have extra armor, which is indicated by the total amount of armor appearing in green on the tooltip. Rings, weapons, amulets and trinkets have no base armor, but may have bonus armor.
Resistance - Decreases the damage taken from magical attacks.
Resilience - Decreases the damage taken from enemy players. Resilience is increased through equipment with resilience which is found on PvP gear. Resilience does not have any effect against an npc.
Base statistics affect attack power (which contributes to DPS) as follows:
Strength will always contribute to the physical melee attack power for all classes.
Rogues, hunters and shamans can also use Agility in addition to Strength to increase their base physical melee attack power.
Druids in Cat Form can also use Agility to increase their base physical melee attack power. However, Agility also affects critical strike percentage which directly affects Cat Form abilities such as Primal Fury. This gives an added attack power equivalence.
Agility is the only primary statistic to affect physical ranged attack power (bows and crossbows, guns, throwing weapons) for all classes capable of using them. This is especially important for hunters.
Wand damage is not affected by a primary statistic.
Critical Strikes
Agility will increase the chance to score a critical strike with both physical ranged and melee damage for all classes. The amount needed per point varies by class.
Intellect will increase the chance to score a critical strike with spells. For a mage at level 60, the rate is 1% per 59.5 points of intellect.
Critical strike rating increases the chance for both spell and physical affects to score a critical strike.
Dodge
Agility will determine a character's chance to dodge an attack. Rogues and druids (as of 2.03) gain a much stronger bonus to dodge than other classes.
Fighting with two weapons, using off-hand, two-handed
Armor Penetration: Stat has been removed from gear, all previous items with ArP have had it converted to Crit or Haste depending on which stats was not present in the item. (Still exists in skills, debuffs, etc.)
Mana Regeneration: Stat has been removed, all previous items with MP5 have had it converted to Spirit.
Spell power: Has been removed on most items. (Usually found only on weapons now.)
Resilience: No longer reduces chance of receiving a critical hit and is now a flat reduction on damage taken from other players.
Agility: The amount of agility required per percentage of dodge has been increased by 15%. This change required recalibrating the amount of dodge a player has with 0 agility by a slight amount as well, so all players will see their dodge percentage vary a small amount.
Block rating: The amount of bonus block value on all items has been doubled. This does not affect the base block value on shields or block value derived from strength.
Dodge Rating: The amount of dodge rating required per percentage of dodge has been increased by 15%. This is before diminishing returns. Combined with other changes, this makes dodge rating and parry rating equally potent before diminishing returns apply.
Parry Rating: The amount of parry rating required per percentage of parry has been reduced by 8%. This is before diminishing returns. Combined with other changes, this makes dodge rating and parry rating equally potent before diminishing returns apply. Parry still diminishes more quickly than dodge.
Resilience: No longer reduces the amount of damage done by damage-over-time spells, but instead reduces the amount of all damage done by players by the same proportion. The other effects of resilience (reducing critical chance, critical damage and mana drain effects) have not changed.