1. A computer-implemented method comprising: receiving a search result obtained in response to a query, wherein the search result identifies a resource and has an associated score S; computing a recent impression probability for the query for a recent time period and an overall impression probability for the query for an overall time period, wherein each impression probability corresponds to a ratio of (i) a count of search result impressions selected by users to (ii) a count of all search result impressions presented to users in the respective time periods, wherein the search result impressions were impressions provided in response to the query by a search engine during the respective time period, and wherein the overall time period is a time period that began before the recent time period and is longer than the recent time period; computing a QtoA ratio of the recent impression probability to the overall impression probability; determining that users prefer newer resources over older resources for the query based on the QtoA ratio; determining that the resource is a new resource; and associating a new score S′ with the resource in place of S, wherein the new score S′ signifies a better result than the score S signifies, based on determining, that users prefer newer resources over older resources for the query and that the resource is a new resource.
2. The method of claim 1 , wherein the overall time period includes the recent time period.