Thus, inasmuch as highest PMI values tend to capture multi-word expressions (South and Africa; Merill and Lynch), morphological variants (bids and bidding), or synonyms (mergers and takeovers), their proportion in word type pairs does not seem to give a clear signal regarding the quality of writing.
8 the area of moderately high PMI values (from PMI=2.5 to PMI=3.67 in Figure 2) produces a very consistent picture, with only two points out of 48 in that interval 9 lacking significant positive correlation with essay score (p2 at PMI=3.17 and p5 at PMI=3).