4. The system of claim 1 , wherein the diversity index is a Shannon index.
1. A system for expanding a search, the system comprising: a processor and executable instructions accessible on a computer-readable medium that, when executed, cause the processor to perform operations comprising: calculate a diversity index for a plurality of query terms included in a plurality of other queries associated with a query, the diversity index being a measure of diversity among the plurality of query terms, the diversity index relating to differences among the plurality of query terms; compare the diversity index to a threshold value; and expand the query with one or more of the plurality of query terms based on the comparison.