1. A method that is executed by a computer processor on a computing device, the method comprising: receiving a search query; receiving a first search result list returned by a first ranker system responsive to the search query; receiving a second search result list returned by a second ranker system responsive to the search query; employing a first classifier to predict whether a search preference judgment of the first search result list and the second search result list for the search query indicates a quality difference between the first search result list and the second search result list, wherein the first classifier predicts whether the search preference judgment indicates the quality difference based upon values of features of the search query, the first search result list, and the second search result list; and excluding the search query, the first search result list, and the second search result list from a first set of search queries and search result list pairs to be manually judged for search preference judgments when the first search result list and the second search result list for the search query are predicted to lack the quality difference.