Lethality

From WoW: IncGamers World of Warcraft Wiki

Talent: Lethality
Effect: Increases the Critical Strike damage bonus of your Sinister Strike, Gouge, Backstab, Ghostly Strike, Mutilate, Shiv, and Hemorrhage abilities by 30%.
Statistics: Rank 1 = +6%, Rank 2 = +12%, Rank 3 = +18%, Rank 4 = +24%, Rank 5 = +30%.