ROUGE

# Definition

$$ \text{ROUGE-N} = \frac{\sum_{S \in \{\text{Reference summaries}\}} \sum_{\text{gram}_n \in S} \text{Count}_{\text{match}}(\text{gram}_n)}{\sum_{S \in \{\text{Reference summaries}\}} \sum_{\text{gram}_n \in S} \text{Count}(\text{gram}_n)} $$

Or we can write it as an N-gram recall:

$$ \frac{\text{Total matching N-grams}}{\text{Total N-grams}} $$

# Types of ROUGE:

• ROUGE-1: Words (tokens)
• ROUGE-2: Bigrams
• ROUGE-L: Longest common subsequence
• ROUGE-Lsum: Summary-level ROUGE-L