Whereas ROUGE tries to maximize agreement with all gold summaries, we are satisfied if there exists even one gold intersection sentence that is sufficiently similar to the given candidate sentence.
to calculate the precision of a given candidate intersection sentence c ∈ C, we take the best-matching gold sentence g, and calculate the portion of n-grams in c that are covered by g. Similarly, a gold sentence's recall is measured versus the best-matching c ∈ C. We define an intersection set's precision and recall by taking the averages.