11. A data processing system for selecting content for presentation to a user, the data processing system comprising one or more processors configured to: identify a plurality of topics for a document requested by a user; determine, for each topic of the plurality of topics, a respective confidence score for a correlation between the respective topic and the document, such that a sum of all determined confidence scores for the document is a mathematical constant, a first topic determined to have a first confidence score for a correlation between the first topic and the document; determine, for the first topic, a first sentiment score indicating a sentiment towards the first topic; determine, for a candidate content item, a predicted acceptance score based on the first confidence score, the first sentiment score, and acceptance history data for the candidate content item; and select the candidate content item for presentation to the user, by a computer system, from a plurality of candidate content items, based, at least in part, on the predicted acceptance score.
11. A data processing system for selecting content for presentation to a user, the data processing system comprising one or more processors configured to: identify a plurality of topics for a document requested by a user; determine, for each topic of the plurality of topics, a respective confidence score for a correlation between the respective topic and the document, such that a sum of all determined confidence scores for the document is a mathematical constant, a first topic determined to have a first confidence score for a correlation between the first topic and the document; determine, for the first topic, a first sentiment score indicating a sentiment towards the first topic; determine, for a candidate content item, a predicted acceptance score based on the first confidence score, the first sentiment score, and acceptance history data for the candidate content item; and select the candidate content item for presentation to the user, by a computer system, from a plurality of candidate content items, based, at least in part, on the predicted acceptance score. 14. The system of claim 11 , wherein the predicted acceptance score is a predicted click-through rate.