1. A method, implemented on at least one computing device each of which has at least one processor, storage, and a communication platform connected to a network for evaluating query suggestion quality, the method comprising the steps of: providing a plurality of query suggestions in a ranking to a user; detecting a selection of one of the plurality of query suggestions, wherein the selection causes modification of the position of the selected query suggestion in the ranking; determining a position of the selected one of the plurality of query suggestions in the ranking; and calculating a quality measure of the plurality of query suggestions based, at least in part, on the selection and the position of the selected one of the plurality of query suggestions, wherein the plurality of query suggestions in the ranking are provided to a plurality of users; and wherein the quality measure of the plurality of query suggestions is determined based on a total number of query suggestions in the plurality of query suggestions whose positions are modified in response to the selection.