In our study, we use pointwise mutual information (Cover and Thomas, 1991) to measure association strength, which has been proved effective in the task of semantic relation identification (Pantel and Pennacchiotti, 2006).
under pointwise mutual information (PMI), the strength of association between two events x and y is defined as follows: the association between a pattern p and a positive seed pair s: where |(E i ,p,E j )| is the count of strings matched by pattern p instantiated with E i and E j .