What are the best ways to evaluate a sequence-to-sequence model's performance?

Sequence-to-sequence models are widely used for natural language processing tasks such as machine translation, text summarization, and speech recognition. They consist of an encoder that encodes the input sequence into a latent representation, and a decoder that generates the output sequence from the latent representation. But how can we measure how well a sequence-to-sequence model performs on a given task? In this article, we will explore some of the best ways to evaluate a sequence-to-sequence model's performance, and the advantages and disadvantages of each method.

1 BLEU score

One of the most popular metrics for evaluating sequence-to-sequence models is the BLEU score, which stands for bilingual evaluation understudy. The BLEU score compares the output sequence of the model with one or more reference sequences provided by human experts, and calculates the n-gram precision and brevity penalty. The n-gram precision measures how many n-grams (sequences of n words) in the output sequence match those in the reference sequences, while the brevity penalty penalizes the output sequence if it is shorter than the reference sequences. The BLEU score ranges from 0 to 1, where 1 means a perfect match with the reference sequences. The BLEU score is easy to compute and widely used, but it also has some limitations. For example, it does not account for semantic similarity, syntactic variation, or word reordering, and it may not correlate well with human judgments of quality.

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Shreya Khandelwal

LinkedIn Top Voices | Data Scientist @IBM | GenAI | LLMs | AI & Analytics | 10 x Multi- Hyperscale-Cloud Certified
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BLEU (Bilingual Evaluation Understudy) is a widely used metric for evaluating the quality of machine-generated text, including translations produced by seq2seq models. It measures the overlap between the generated sequence and one or more reference sequences, providing a score between 0 and 1, where higher scores indicate better performance.

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Vineet Yadav

Machine Learning & Artificial Intelligence||MLOps & Cloud computing||Generative AI & LLM Models ||Computer Vision & NLP||Semantic Web & Knowledge Graph||Graph NN & Graph ML||8x Azure||3X GCP|| IIIT Hyderabad
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BLEU score is a precision based metric. It computes the count of correct tokens or ngrams divided by the number of tokens or ngrams which are present in generated text. It extracts all possible n-gram sequence by varying the length of n-gram. It computes n-gram precision for each variation of the length. It also uses brevity penalty, which has a smaller value when the generated text is smaller in length as compared to the reference text. It computes the geometric mean of n-gram precision for different length of ngram and multiply it with brevity score. BLEU score is used in machine translation, where precision is more important. Although, there are limitations, as BLEU score cannot handle synonyms in translation.

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2 ROUGE score

Another common metric for evaluating sequence-to-sequence models is the ROUGE score, which stands for recall-oriented understudy for gisting evaluation. The ROUGE score is mainly used for text summarization tasks, where the goal is to produce a concise summary of a longer text. The ROUGE score compares the output summary of the model with one or more reference summaries provided by human experts, and calculates the recall and f-measure of n-grams, words, or sentences. The recall measures how many n-grams, words, or sentences in the reference summaries are covered by the output summary, while the f-measure combines the precision and recall into a single score. The ROUGE score ranges from 0 to 1, where 1 means a perfect match with the reference summaries. The ROUGE score is useful for measuring the informativeness and coverage of the output summary, but it also has some drawbacks. For instance, it does not account for coherence, readability, or relevance, and it may not capture the salience or novelty of the output summary.

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Shreya Khandelwal

LinkedIn Top Voices | Data Scientist @IBM | GenAI | LLMs | AI & Analytics | 10 x Multi- Hyperscale-Cloud Certified
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ROUGE Score (Recall-Oriented Understudy for Gisting Evaluation) evaluates the overlap between the generated and reference sequences in terms of n-grams, recall, precision, and F1 score. It is commonly used for evaluating text summarization tasks.

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3 METEOR score

A more recent metric for evaluating sequence-to-sequence models is the METEOR score, which stands for metric for evaluation of translation with explicit ordering. The METEOR score is mainly used for machine translation tasks, where the goal is to produce a fluent and accurate translation of a source text. The METEOR score compares the output translation of the model with one or more reference translations provided by human experts, and calculates the harmonic mean of unigram precision and recall, with several extensions. The extensions include stemming, synonymy, paraphrasing, and word order. The METEOR score ranges from 0 to 1, where 1 means a perfect match with the reference translations. The METEOR score is designed to address some of the limitations of the BLEU score, such as the lack of semantic similarity, syntactic variation, and word reordering. The METEOR score is more correlated with human judgments of quality, but it also has some challenges. For example, it requires more linguistic resources, such as stemmers, dictionaries, and paraphrase tables, and it may not be consistent across different languages.

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Shreya Khandelwal

LinkedIn Top Voices | Data Scientist @IBM | GenAI | LLMs | AI & Analytics | 10 x Multi- Hyperscale-Cloud Certified
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METEOR (Metric for Evaluation of Translation with Explicit ORdering) considers precision, recall, stemming, synonymy, and stemming-based penalties to assess the quality of machine-generated text. It is particularly useful for evaluating seq2seq models in natural language generation tasks.

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4 Other metrics

Besides the BLEU, ROUGE, and METEOR scores, there are also other metrics for evaluating sequence-to-sequence models, such as the TER score, the CIDEr score, the BERTScore, and the CHRF score. Each of these metrics has its own strengths and weaknesses, and may be more suitable for different tasks, domains, or languages. Therefore, it is important to choose the appropriate metric for the specific goal and context of the evaluation, and to complement it with other methods, such as human evaluation, error analysis, or ablation studies. By using a combination of metrics and methods, we can gain a more comprehensive and reliable understanding of the performance of a sequence-to-sequence model.

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5 Here’s what else to consider

This is a space to share examples, stories, or insights that don’t fit into any of the previous sections. What else would you like to add?

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What are the best ways to evaluate a sequence-to-sequence model's performance?

1

2

3

4

5

1 BLEU score

2 ROUGE score

3 METEOR score

4 Other metrics

5 Here’s what else to consider

Data Mining

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What are the best ways to evaluate a sequence-to-sequence model's performance?

1

2

3

4

5

1 BLEU score

2 ROUGE score

3 METEOR score

4 Other metrics

5 Here’s what else to consider

Data Mining

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