Evaluating the Evaluation of Diversity in Natural Language Generation
Paper · 2021 · Guy Tevet and Jonathan Berant
Summary
NLG systems are expected to produce varied outputs, but the field has no agreed-upon way to measure diversity. It is also unclear how to check whether a given diversity metric works. Tevet and Berant propose a meta-evaluation framework. A "tester" (a neural model or a human) generates response sets for a context, guided by a diversity parameter. A metric's quality is the Spearman correlation between its scores and that parameter. They apply this in two tests:
- decTest: the parameter is a decoding setting such as softmax temperature.
- conTest: crowdworkers deliberately write sets with low or high content diversity while keeping form diversity high.
The authors compare n-gram metrics, neural similarity-based metrics and several Human Diversity Score (HDS) variants. N-gram metrics follow decoding parameters closely, which suggests that decoding mainly changes surface form rather than meaning. These metrics do poorly on content diversity. Neural metrics, especially sent-BERT, do better, but humans remain clearly ahead. The authors also release the McDiv benchmark and their code, giving future diversity metrics a common testbed.
Key points
- Metrics are scored by Spearman's ρ against the diversity parameter. Optimal single-threshold classifier accuracy (OCA) is reported alongside.
- In conTest, the human metric absHDS clearly beats automatic metrics:
- storyGen: absHDS ρ = 0.85, sent-BERT 0.77, distinct-n 0.57.
- respGen: absHDS 0.63, sent-BERT 0.59, distinct-n 0.34.
- McDiv contains 6K context–response-set pairs, 2K each for storyGen, respGen and promptGen.
- McDiv nuggets is a 3K subset in which distinct-n correlation is zero, so form cues are neutralized. On respGen here, absHDS reaches ρ ≈ 0.7 versus 0.6 for sent-BERT.
- Stability experiments set the HDS budget at 200 sets with 10 ratings per set. Asking raters directly about content (aspHDS) gave little gain over absHDS.
Institutions
📚 Shelves 4The field of science this work belongs to (OpenAlex fields).Computer Science · 9,085 worksArtificial Intelligence · 8,888 worksArts and Humanities · 9,296 worksLanguage and Linguistics · 9,206 works
🧭 Topics 2Research subjects and languages the work is about.Evaluation & benchmarks · 685 worksText generation · 145 works
Cite
Cite as Guy Tevet and Jonathan Berant. 2021. Evaluating the Evaluation of Diversity in Natural Language Generation. Proceedings of the 16th Conference of the European Chapter of the Association for Computational Linguistics: Main Volume.
@inproceedings{tevet2021evaluating,
title = {{Evaluating the Evaluation of Diversity in Natural Language Generation}},
author = {Guy Tevet and Jonathan Berant},
booktitle = {Proceedings of the 16th Conference of the European Chapter of the Association for Computational Linguistics: Main Volume},
year = {2021},
doi = {10.18653/v1/2021.eacl-main.25},
url = {https://doi.org/10.18653/v1/2021.eacl-main.25}
}References
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