We observe that the model trained on ROUGE-2 is performing better than the model trained on ROUGE-1, although learning the ROUGE-2 scores seems to be harder than learning ROUGE-1 8 The symbol * indicates that the difference compared to the previous best baseline is significant with p ≤ 0.05. scores (as shown in table 2).
errors and approximations propagate less easily in ROUGE-2, because the number of bi-grams in the intersection of two given sentences is far less.