Observations

Given the difficulty encountered by human evaluators in determining topic changes within the evaluation documents, it is possible that it is not sensible to talk about `topics' within a spoken dialogue as it is within written text. Because written text is laid out in a logical progression or exploration of ideas, its topics are intentional - the author wishes to convey several points, and addresses them in a sensible order. In contrast, while some structured meeting dialogues contain a series of `action items', many spoken dialogues are unstructured, and comprise largely unplanned discussions concerning topics not critical (or even related) to the agendae of the speakers. It is possible, therefore, that spoken dialogue contains many sections which cannot reasonably be classified as `topics' at all, at least in the same sense that Hearst [6] and Beeferman [1] use. When a conversation can be said to have `digressed' from its original topic, it is not always clear that it has entered another.