1. A computer-readable storage medium storing computer-executable instructions for controlling a computing system to score discussion threads being in a question-and-answer form, each discussion thread having posts with terms, the computer-executable instructions comprising: a component that provides a query; a component that identifies features of a discussion thread, to features including a combined post feature representing a collection of the terms of multiple posts of a discussion thread; a component that generates feature scores for the features, the feature score for the combined post feature indicating relevance of the terms of the collection to the query; and a component that generates a relevance score for a discussion thread based on combining the feature scores for the discussion thread.