6. A computer-implemented method comprising: receiving a query expansion source, a query expansion candidate, and feature data for the query expansion source and the query expansion candidate, the feature data comprising information for a plurality of features, the plurality of features comprising a measure of price divergence for the query expansion source and the query expansion candidate, the measure of price divergence being a measure of similarity between a distribution of prices of item listings returned as results for a search on the query expansion source and a distribution of prices of item listings returned as results for a search on the query expansion candidate, and the measure of price divergence comprising a Student's t-statistic; determining whether the query expansion candidate qualifies as an expansion of the query expansion source based on an analysis of the information for the plurality of features; and assigning the query expansion candidate as an expanded query of the query expansion source in a query expansion dictionary in response to a determination that the query expansion candidate qualifies as an expansion of the query expansion source.
6. A computer-implemented method comprising: receiving a query expansion source, a query expansion candidate, and feature data for the query expansion source and the query expansion candidate, the feature data comprising information for a plurality of features, the plurality of features comprising a measure of price divergence for the query expansion source and the query expansion candidate, the measure of price divergence being a measure of similarity between a distribution of prices of item listings returned as results for a search on the query expansion source and a distribution of prices of item listings returned as results for a search on the query expansion candidate, and the measure of price divergence comprising a Student's t-statistic; determining whether the query expansion candidate qualifies as an expansion of the query expansion source based on an analysis of the information for the plurality of features; and assigning the query expansion candidate as an expanded query of the query expansion source in a query expansion dictionary in response to a determination that the query expansion candidate qualifies as an expansion of the query expansion source. 7. The method of claim 6 , wherein the feature data is extracted from data of an e-commerce website, the data of the e-commerce website comprising at least one of user behavioral data and item listing data.