The pointwise mutual information (PMI) between two words x and y compares the probability of observing the two words together (their joint probability) to the probabilities of observing x and y independently (the probability of occurring together by chance) (Church and Hanks, 1991) The probabilities can be approximated by: , where C denotes frequency counts and N is the total number of words in the corpus.
: , where N can be ignored in comparisons.