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What are the differences between the BLEU metric and ROUGE?

BLEU and ROUGE are both automated metrics for evaluating the quality of text generated by NLP models, but they measure different aspects. BLEU primarily assesses precision (correctness of matches), while ROUGE emphasizes recall (comprehensiveness of content captured).

BLEU calculates the n-gram precision between candidate text and reference texts, penalizing overly short outputs. It is highly sensitive to exact word matches and often used for machine translation evaluation. ROUGE employs various measures (like ROUGE-N, ROUGE-L, ROUGE-SU) focusing on the overlap of n-grams, longest common subsequences, or skip-grams, highlighting recall. It is the standard metric for summarization tasks. BLEU penalizes unmatched candidate words, while ROUGE effectively penalizes missing content from the reference.

These metrics serve distinct evaluation purposes. BLEU is the established benchmark for assessing the fluency and accuracy of machine translation output. Conversely, ROUGE is the primary metric for gauging the coverage and content recall in text summarization systems, measuring how well the summary captures key points from the source(s). They are valuable tools complementing human judgment in specific NLP domains.

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