A Critical Evaluation of Evaluations for Long-form Question Answering
Paper · 2023 · Fangyuan Xu, Yixiao Song, Mohit Iyyer et al.
Summary
Evaluating long-form question answering (LFQA) is hard because answers are open-ended. Earlier work mostly relied on crowdworkers' A/B preferences and string-overlap metrics such as ROUGE. Xu et al. study both human and automatic evaluation of long answers. They recruited domain experts in seven fields through Upwork. Each expert compared pairs of answers to recent Reddit ELI5 and AskHistorians questions and wrote a paragraph explaining the choice. Pairs were either two human answers with different upvote counts, or a top human answer against zero-shot output from GPT-3 text-davinci-002.
The justifications show that experts weigh completeness and factual accuracy above surface traits like conciseness or detail. Experts also often disagree, because they value these properties differently.
The authors then tested 12 automatic metrics against expert and existing crowd judgments. None reliably predicted overall preference, though some tracked specific aspects such as coherence or faithfulness.
The authors argue that a single overall quality score is not meaningful. They recommend expert annotators and evaluation along separate dimensions such as factuality, completeness and ease of understanding.
Key points
- Released dataset: 260 expert ratings with justifications covering 140 answer pairs across seven domains (e.g., biology, physics, economics, law, history). It cost $845 at $3.25 per question, and experts reported 15–30 minutes per item. The data is released under the MIT license.
- Expert preferences: On average, experts chose the more-upvoted human answer 62.4% of the time in H/H pairs and the GPT-3 answer 61.8% of the time in H/M pairs. Fleiss' κ ranged from 0.40 to 0.65 in the domains with multiple experts.
- Automatic metrics: None of the 12 metrics matched overall human preference. A simple answer-length baseline was surprisingly competitive, which exposes how brittle current metrics are.
- Fine-grained aspects:
- QAFactEval performed best on factuality but needs evidence documents.
- RankGen showed promise for modeling specific answer qualities.
- Self-BLEU performed competitively on coherence.
- Benchmark scope: Existing human annotations from HURDLES and WebGPT (overall preference, factuality, coherence) are compiled alongside the new data into a unified benchmark. ROUGE and BERTScore agreed on 63% of answer pairs.
Institutions
📚 Shelves 5 Computer Science · 9,086 works Artificial Intelligence · 8,889 works Arts and Humanities · 9,296 works Language and Linguistics · 9,206 works Information Systems · 523 works
🧭 Topics 2 Evaluation & benchmarks · 685 works Question answering · 242 works
Cite
Cite as Fangyuan Xu, Yixiao Song, Mohit Iyyer and Eunsol Choi. 2023. A Critical Evaluation of Evaluations for Long-form Question Answering. Proceedings of the 61st Annual Meeting of the Association for Computational Linguistics (Volume 1: Long Papers).
@inproceedings{xu2023critical,
title = {{A Critical Evaluation of Evaluations for Long-form Question Answering}},
author = {Fangyuan Xu, Yixiao Song, Mohit Iyyer and Eunsol Choi},
booktitle = {Proceedings of the 61st Annual Meeting of the Association for Computational Linguistics (Volume 1: Long Papers)},
year = {2023},
doi = {10.18653/v1/2023.acl-long.181},
url = {https://doi.org/10.18653/v1/2023.acl-long.181}
}References
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