1. A computerized method for determining the performance of a plurality of versions of a given advertisement, the method comprising: identifying a modified advertisement from a result set in response to a given query; retrieving a first version of the modified advertisement and associated click through data; retrieving a second version of the modified advertisement and associated click through data; electronically calculating, via a processing device, a clickability score for the first version of the modified advertisement using the click through data associated with the first version of the modified advertisement, the clickability score for the first version of the modified advertisement comprising a prediction of a click through rate for the first version of the modified advertisement in response to the given query; electronically calculating, via the processing device, a clickability score for the second version of the modified advertisement using the click through data associated with the second version of the modified advertisement, the clickability score for the second version of the modified advertisement comprising a prediction of a click through rate for the second version of the modified advertisement in response to the given query; determining a difference in clickability scores between the first advertisement and the second advertisement; modifying the clickability score associated with the first version of the modified advertisement based upon the difference in clickability scores and storing said modified clickability score; determining a bid price for display of the modified advertisement at a selected position in a ranked list of advertisements, the bid price comprising a maximum amount of money to be paid for display of the modified advertisement at the selected position in the ranked list of advertisements; electronically calculating, via the processing device, an expected bid revenue for the first version of the modified advertisement using the modified clickability score associated with the first version of the modified advertisement and the bid price, the expected bid revenue for the first version of the modified advertisement providing an indication of revenue to be received from display of the first version of the modified advertisement at the selected position in a ranked list of advertisements; electronically calculating, via the processing device, an expected bid revenue for the second version of the modified advertisement using the clickability score associated with the second version of the modified advertisement and the bid price, the expected bid revenue for the second version of the modified advertisement providing an indication of revenue to be received from display of the second version of the modified advertisement at the selected position in a ranked list of advertisements; and ranking the first and second versions of the modified advertisement based on their expected bid revenues.