Letting the probability of a word appearing in a retelling be p 1 and the probability of that word appearing in all other retellings be p 2 , we can express the odds ratio as follows: A large tf-idf or log odds score indicates that the word j is very specific to the retelling i, which in turn suggests that the word might be unexpected or inappropriate in the larger context of the NNM narrative.
we expect that the words with higher association measure scores are likely to be the words that were manually identified as unexpected in the context of the NNM narrative.