4. The method of claim 2 , further comprising: calculating the observed historical click through rate as a ratio representing a total number of times users have selected the specific search result in response to a particular search query to a total number of times users have selected other search results in response to the particular search query, the other search results being different from the specific search result.
4. The method of claim 2 , further comprising: calculating the observed historical click through rate as a ratio representing a total number of times users have selected the specific search result in response to a particular search query to a total number of times users have selected other search results in response to the particular search query, the other search results being different from the specific search result. 5. The method of claim 4 , wherein the search query is the same as the particular search query.