24. The computer-readable storage media of claim 23 , wherein determining, based on the training conversational turns in the first set of training data, that the natural language understanding engine is likely to generate inaccurate annotations of other conversational turns that are similar to the first input conversational turn comprises: identifying training conversational turns in the training data that are similar to the first input conversational turn according to a similarity measure.
25. The computer-readable storage media of claim 24 , wherein determining, based on the training conversational turns in the first set of training data, that the natural language understanding engine is likely to generate inaccurate annotations of other conversational turns that are similar to the first input conversational turn comprises: determining that there are less than a threshold number of training conversational turns that are similar to the first input conversational turn according to the similarity measure.