1. A computer implemented method of selecting content for presentation to a user, the method comprising: identifying a plurality of topics for a document requested by a user; determining, 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; determining, for the first topic, a first sentiment score indicating a sentiment towards the first topic; determining, 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 selecting 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.