In order to compare language models, we turned to techniques from adaptive NLP (i.e., on the basis of genre and type distinctions) (Illouz, 2000).
we employed the cross entropy 4 between two language models ¡ ¡ and ¡ ¢ , defined as follows (where is the probability that to be a model of randomly selected documents and ¡ ¢ a model of a subset of texts that are associated with the cluster, then a greater-than-chance value would be an indicator that the cluster in the semantic side is being correlated with changes in the text side.