24. The machine-readable storage of claim 23 wherein providing the model for use with the search engine comprises providing the first and second models for use with the search engine, wherein the search engine is configured to use predictive outputs of the first and second models to adjust respective ranking scores of the given search results obtained as the search results for the given query to reduce presentation bias in a presentation of the given search results, and wherein the search engine is configured to provide the presentation bias and relevance features of the given search results as input to the first and second models.
23. The machine-readable storage of claim 19 wherein training the model comprises: training a first model using the obtained presentation bias features to predict a click through rate based on input comprising the one or more presentation bias features; and training a second model using the obtained relevancy features to predict a click through rate based on input comprising the one or more relevancy features.