1. A computer-implemented method comprising: obtaining a plurality of image search results responsive to a received query; identifying a first set of search results that referenced a first corresponding set of images and were previously provided to a first set of users that previously submitted first queries that correspond to the received query; identifying a second set of search results that referenced a second corresponding set of images and were previously provided to a second different set of users that submitted second queries that correspond to the received query and have a characteristic matching a characteristic of a user that submitted the received query; determining, by one or more data processing apparatus, a result similarity based on a number of same images that are included in both of the first corresponding set of images and the second corresponding set of images; and ranking, based on the result similarity and by one or more data processing apparatus, the plurality of image search results based on one of first performance data for the first set of search results or second performance data for the second set of search results.