1. A method performed by one or more computers, the method comprising: receiving a first search query from a user device, wherein the first search query has been determined to relate to a first entity of a first entity type, and wherein one or more entities of a second entity type have a predetermined relationship with the first entity; receiving search results for the first search query provided by a search engine, wherein each of the search results identifies a respective resource; determining that a count of search results identifying a resource containing a reference to the first entity satisfies a first threshold value; determining that a count of search results identifying a resource having the second entity type as a relevant entity type satisfies a second threshold value; and transmitting information identifying the one or more entities of the second entity type to the user device as part of the response to the first search query.