16. A computer-program product tangibly embodied in a non-transitory, computer-readable storage medium that stores instructions, the instructions executable by a data processing apparatus for performing operations including: accessing, using one or more processors, a mood evaluation index from a first electronic data store, wherein the mood evaluation index maps text to mood categories, wherein text describes a state associated with at least one of the mood categories, and wherein a mood category is associated with a state; mapping text to a mood category using the mood evaluation index, wherein the mood evaluation index associates a state with the text; calculating a mood weight for the text, wherein mood weights are calculated using a mood evaluation index, and wherein mood weights represent an intensity of the state that the text describes; accessing a message from a second electronic data store, wherein the message includes text mapped by the mood evaluation index; using the mood evaluation index to identify text included in the message that is mapped to a mood category; determining whether a modifier is in proximity to identified text; adjusting the mood weight of the identified text that is in proximity to the modifier; summing the mood weights of the identified text, wherein summing includes determining a category score corresponding to the mood category; and outputting the category score corresponding to the mood category to a third electronic data store, wherein the modifier is a negation, and wherein the adjusting the mood weight of the identified text that is in proximity to the modifier includes changing one of a positive mood to a negative mood or changing a negative mood to a positive mood.
16. A computer-program product tangibly embodied in a non-transitory, computer-readable storage medium that stores instructions, the instructions executable by a data processing apparatus for performing operations including: accessing, using one or more processors, a mood evaluation index from a first electronic data store, wherein the mood evaluation index maps text to mood categories, wherein text describes a state associated with at least one of the mood categories, and wherein a mood category is associated with a state; mapping text to a mood category using the mood evaluation index, wherein the mood evaluation index associates a state with the text; calculating a mood weight for the text, wherein mood weights are calculated using a mood evaluation index, and wherein mood weights represent an intensity of the state that the text describes; accessing a message from a second electronic data store, wherein the message includes text mapped by the mood evaluation index; using the mood evaluation index to identify text included in the message that is mapped to a mood category; determining whether a modifier is in proximity to identified text; adjusting the mood weight of the identified text that is in proximity to the modifier; summing the mood weights of the identified text, wherein summing includes determining a category score corresponding to the mood category; and outputting the category score corresponding to the mood category to a third electronic data store, wherein the modifier is a negation, and wherein the adjusting the mood weight of the identified text that is in proximity to the modifier includes changing one of a positive mood to a negative mood or changing a negative mood to a positive mood. 17. The computer-program product of claim 16 , wherein the modifier is a negation, wherein the instructions executable by the data processing apparatus for performing operations for adjusting the mood weight of the identified text that is in proximity to the modifier includes changing a positive mood to a negative mood or changing a negative mood to a positive mood.