In order to check the robustness of these results, we computed the correlation of individual metric failures between test beds, obtaining 0.67 Pearson for the lowest correlated test bed pair (AE 2004 and CE 2005 ) and 0.88 for the highest correlated pair (AE 2004 and CE 2004 ).
linguistic metrics are represented by grey plots, and black plots represent metrics based on n-gram overlap.