Unifying Human and Statistical Evaluation for Natural Language Generation
Paper · 2019 · Tatsunori B. Hashimoto, Hugh Zhang and Percy Liang
Summary
Evaluating text generators is hard because the usual tools each miss something. Human ratings reward fluent output but cannot tell when a model just copies training data or always produces the same answer. Perplexity rewards coverage but barely punishes occasional bad samples. Hashimoto, Zhang and Liang define one target quantity: twice the error of the best classifier that tries to tell reference text from model output. A perfect model gets 1, and a model with no overlap with the reference gets 0. They prove this optimal classifier needs only two values per sentence: its probability under the model and its probability under the reference. Since the reference probability cannot be computed, they replace it with crowdsourced "typicality" ratings. HUSE is the leave-one-out error of a k-nearest-neighbour classifier over the length-normalised model log-probability and the human score. Experiments on summarization and chit-chat dialogue show two things:
- HUSE exposes diversity problems that pure human evaluation misses.
- Quality-boosting tricks like annealing actually lower HUSE.
Key points
- The target metric L* equals 1 minus the total variation distance between the model and reference distributions. HUSE is an upper bound on it that is never looser than human-only evaluation: L(φ_hj) ≥ L(φ_huse) ≥ L*.
- The features are log p_model(y|x) divided by sentence length, plus HJ(x, y). HJ is the average 1–5 typicality rating from 20 Amazon Mechanical Turk workers.
- On the Reddit corpus, HJ correlated strongly with a sentence's log-frequency (r = 0.92), which supports using it as a proxy for log p_ref.
- The tasks studied were language modeling, chit-chat dialogue, story generation and summarization.
- Code, data and experiments are released on CodaLab.
Institutions
Fields, topics and concepts
📚 Shelves 4The field of science this work belongs to (OpenAlex fields).Computer Science · 18,614 worksArtificial Intelligence · 17,965 worksArts and Humanities · 17,450 worksLanguage and Linguistics · 17,296 works
🧭 Topics 2Research subjects and languages the work is about.Evaluation & benchmarks · 1,341 worksText generation · 214 works
Cite
Cite as Tatsunori B. Hashimoto, Hugh Zhang and Percy Liang. 2019. Unifying Human and Statistical Evaluation for Natural Language Generation. arXiv:1904.02792.
@misc{hashimoto2019unifying,
title = {{Unifying Human and Statistical Evaluation for Natural Language Generation}},
author = {Tatsunori B. Hashimoto, Hugh Zhang and Percy Liang},
year = {2019},
doi = {10.48550/arxiv.1904.02792},
eprint = {1904.02792},
archivePrefix = {arXiv},
url = {https://doi.org/10.48550/arxiv.1904.02792}
}References
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