13. A non-transitory computer-readable storage medium storing computer-executable code comprising instructions for: storing, by a processor, communications between members of an online forum, each communication representing a message received by the server from a particular client device via a network and sent by the server to another client device via the network; receiving, by the processor, from a client device, a topic associated with the communications; determining, by the processor for each of a plurality of terms, a frequency of co-occurrence of the term with the topic in the communications; selecting, by the processor, a top term from the plurality of terms based on the frequency of co-occurrence of each of the plurality of terms with the topic; receiving, from the client device, information describing a first time interval selected using a user interface control presented via a display of the client device; determining, by the processor, a first aggregate demographic value based on a demographic attribute of the members that used the top term during the first time interval; receiving, from the client device, information describing a second time interval selected using the user interface control, wherein the second time interval is subsequent to the first time interval; determining, by the processor, a second aggregate demographic value based on the demographic attribute of the members that used the top term during the second time interval; and presenting on the display of the client device, a user interface displaying a graph including at least one axis representing the demographic attribute of the members that used the top term and a geometric shape representing the top term co-occurring with the topic in the communications, the user interface presenting variation of the demographic attribute of the members that used the top term with respect to time based on the first aggregate demographic value and the second aggregate demographic value.
19. The non-transitory computer-readable storage medium of claim 13 , wherein the demographic attribute comprises age.