23. A computer-implemented method comprising: receiving a first search result obtained in response to a query, wherein the first search result identifies a resource and has an associated score S; computing a first probability that a particular search result provided in response to the query in a recent time period will be selected when a particular user is presented with an opportunity to select the particular search result; computing a second probability that the particular search result provided in response to the query in an overall time period will be selected when the particular user is presented with an opportunity to select the particular search result; computing a QtoA ratio of the first probability to the second probability; determining, based on the QtoA ratio, that users in the recent time period preferred newer resources for the query than users in the overall time period; determining that the resource is a new resource; and applying a boosting function to S to compute a new score S′ for the resource, wherein S′ has a boosted value that is higher relative to boosted scores of other resources that are older than the resource.
23. A computer-implemented method comprising: receiving a first search result obtained in response to a query, wherein the first search result identifies a resource and has an associated score S; computing a first probability that a particular search result provided in response to the query in a recent time period will be selected when a particular user is presented with an opportunity to select the particular search result; computing a second probability that the particular search result provided in response to the query in an overall time period will be selected when the particular user is presented with an opportunity to select the particular search result; computing a QtoA ratio of the first probability to the second probability; determining, based on the QtoA ratio, that users in the recent time period preferred newer resources for the query than users in the overall time period; determining that the resource is a new resource; and applying a boosting function to S to compute a new score S′ for the resource, wherein S′ has a boosted value that is higher relative to boosted scores of other resources that are older than the resource. 29. The method of claim 23 , further comprising: determining a query value Q for the query, wherein the query value is based on the QtoA ratio; determining a resource value D for the resource, the resource value being based on a function of an age of the resource, F(age); and wherein the boosting function is a boosting function of the query value Q and the resource value D.