The differences between the correlations are statistically significant at p < 0.05 (using Student's t-test) except for the differences between the LSA+SYN system and the baseline, and between the LSA+SYN+SEM system and the LSA+SEM system.
the length of the essays is another issue since longer essays tend to capture more information in their representative vectors which provides the scope for a better similarity matching with the semantic space.