9. A machine readable storage medium encoded with computer program code, wherein when the computer program code is executed by a processor, the processor performs a machine implemented method comprising the steps of: analyzing a plurality of attributes of a sample of online documents using a boosted decision tree and generating a model therefrom; using the model to predict a click through rate (CTR) of an additional online document based on the analyzing; outputting the predicted CTR to a display device, storage medium or network, wherein the plurality of attributes include a CTR of other documents having titles that are the same as or similar to a title of the additional online document; determining similarity of any two documents by cardinality of a difference set that includes non-overlapping terms included in the title of one of the two documents but not included in the title of the other of the two documents; using the model to predict respective CTR of a plurality of additional online documents based on the analyzing; and ranking the plurality of additional online documents by using the respective predicted CTR of each of the plurality of additional online documents as an input factor.
9. A machine readable storage medium encoded with computer program code, wherein when the computer program code is executed by a processor, the processor performs a machine implemented method comprising the steps of: analyzing a plurality of attributes of a sample of online documents using a boosted decision tree and generating a model therefrom; using the model to predict a click through rate (CTR) of an additional online document based on the analyzing; outputting the predicted CTR to a display device, storage medium or network, wherein the plurality of attributes include a CTR of other documents having titles that are the same as or similar to a title of the additional online document; determining similarity of any two documents by cardinality of a difference set that includes non-overlapping terms included in the title of one of the two documents but not included in the title of the other of the two documents; using the model to predict respective CTR of a plurality of additional online documents based on the analyzing; and ranking the plurality of additional online documents by using the respective predicted CTR of each of the plurality of additional online documents as an input factor. 10. The machine readable storage medium of claim 9 , further comprising: rendering the additional online documents or portions thereof for display in order of their respective rankings.