Words are weighted considering their dispersion (global weight) and their conditional probability given a position (local weight).
the weight Assoc, measuring the degree of association between word w and position p, is computed by equation 16: the conditional probability P MLE is estimated by using the maximum likelihood estimate (MLE), which is calculated in (17): where f ðp, wÞ represents the frequency of word w appearing in position p, and FðpÞ is defined, for a particular position, as the total sum of its word frequencies:~i f ðp, w i Þ.