19. The method of claim 18 , wherein the numerical value is based, at least in part, on an aggregate of the one or more conditional probabilities.
18. The method of claim 17 , wherein determining one or more metrics comprises: determining one or more conditional probabilities that the search query terms of each search query occur given the topic of the content item; and determining a numerical value indicating proximity to the topic based, at least in part, on the one or more conditional probabilities.