12. A computer program product encoded on a non-transitory computer-readable medium, operable to cause a data processing apparatus to perform operations comprising: receiving a request to determine whether to assign a classification to a first query; selecting a plurality of search entities that are associated with the first query based on respective user behavior data for the first query associated with each of the search entities; determining a first measure of how many of the plurality of search entities have been assigned the classification; determining that the first measure of how many of the plurality of search entities have been assigned the classification satisfies a classification threshold; in response to determining that the first measure of how many of the plurality of search entities have been assigned the classification satisfies the classification threshold, determining a second measure of how many of a top group of search entities from the plurality of search entities have been assigned the classification, each search entity in the top group of search entities being in a subset of the plurality of search entities having highest respective measures of relevance to the query based on the user behavior data; determining that the first measure of how many of the plurality of search entities have been assigned the classification is consistent with the second measure of how many of the top group of search entities have been assigned the classification; and in response to determining that the first measure of how many of the plurality of search entities have been assigned the classification is consistent with the second measure of how many of the top group of search entities have been assigned the classification, assigning the classification to the first query.
12. A computer program product encoded on a non-transitory computer-readable medium, operable to cause a data processing apparatus to perform operations comprising: receiving a request to determine whether to assign a classification to a first query; selecting a plurality of search entities that are associated with the first query based on respective user behavior data for the first query associated with each of the search entities; determining a first measure of how many of the plurality of search entities have been assigned the classification; determining that the first measure of how many of the plurality of search entities have been assigned the classification satisfies a classification threshold; in response to determining that the first measure of how many of the plurality of search entities have been assigned the classification satisfies the classification threshold, determining a second measure of how many of a top group of search entities from the plurality of search entities have been assigned the classification, each search entity in the top group of search entities being in a subset of the plurality of search entities having highest respective measures of relevance to the query based on the user behavior data; determining that the first measure of how many of the plurality of search entities have been assigned the classification is consistent with the second measure of how many of the top group of search entities have been assigned the classification; and in response to determining that the first measure of how many of the plurality of search entities have been assigned the classification is consistent with the second measure of how many of the top group of search entities have been assigned the classification, assigning the classification to the first query. 16. The computer program product of claim 12 wherein the plurality of identified search entities comprises a plurality of second queries distinct from the first query.