1. A method for predicting click probability in sponsored search results comprising: receiving a search query; identifying advertisements for display in response to the search query, wherein each of the advertisements is associated with a bid amount; predicting a click probability for each of the identified advertisements, wherein the click probability predicting comprises: identifying a set of features to consider for the click probability prediction, wherein each of the features includes either a known or unknown value; imputing an estimate for any of the unknown features; weighting both the known and unknown features; and modeling the weighted features using a variance of the unknown features and dependencies between features; ranking the identified advertisements by multiplying the bid amount by the click probability for each of the advertisements; and providing a search results page in response to the search query, wherein at least a portion of the ranked advertisements are displayed, further where the displayed advertisements are displayed in an order based on the ranking.