Large Language Models are Inconsistent and Biased Evaluators
Paper · 2024 · Rickard Stureborg, Dimitris Alikaniotis and Yoshi Suhara
Summary
LLM-based judges such as GPT-4 are now widely used to score generated text without references. However, earlier work mostly tuned them to match human ratings and paid little attention to how reliable they are. The authors examine two properties of these judges, bias and consistency, in summary evaluation. They use SummEval as a development set and RoSE as a held-out test set. Across more than 560,000 generated outputs from GPT-3.5 and GPT-4, they find three biases. The models favour low-perplexity text (familiarity bias), they distribute scores unevenly and favour round values, and their judgments on one attribute are anchored by ratings they have already given for other attributes. The judges are also unstable: repeated samples agree with each other less than human annotators do, and the models react to prompt changes that a human would consider irrelevant. From these findings the authors derive a set of configuration recipes. Their resulting evaluator significantly beats the previous state of the art on part of RoSE. The work highlights hidden risks of relying on LLM-as-a-judge metrics.
Key points
- Data and setup:
- SummEval provides expert scores for 16 system summaries of each of 100 CNN/Daily Mail articles. It covers Coherence, Consistency, Fluency and Relevance, and agreement with experts is measured with Kendall's τ.
- RoSE spans CNN/Daily Mail, SAMSum and XSum, with recall-style annotations based on Atomic Content Units (ACU).
- Models:
- The analysis uses gpt-3.5-turbo-0301 and gpt-4-0613.
- The final RoSE comparison runs on GPT-4-Turbo against the authors' own re-implementation of G-Eval.
- Perplexity is computed with text-davinci-003.
- Familiarity bias: Mean summary perplexity for GPT-4 Coherence ratings falls sharply as scores rise, from about 8.15 at score 2 to 5.34 at score 5. Expert ratings span a much narrower range (7.03 to 6.36). GPT-4's ratings also correlate negatively with source-document perplexity, while expert ratings show no such link.
- Score granularity: The authors compare several rating formats: 1–5, 1–5 with "strong/weak" word modifiers, GPA-style float values, 1–10, and 1–100. They also test averaging over multiple samples. LLMs often fail to use these finer scales as instructed.
- Result and limitations:
- The recipe-based evaluator significantly outperforms the SOTA on the CNNDM partition of RoSE at 90% confidence. Gains on the other two domains are positive but not significant.
- Only proprietary OpenAI models were tested.
Institutions
📚 Shelves 4The field of science this work belongs to (OpenAlex fields).Computer Science · 9,086 worksArtificial Intelligence · 8,889 worksArts and Humanities · 9,296 worksLanguage and Linguistics · 9,206 works
🧭 Topics 1Research subjects and languages the work is about.Language models & pretraining · 1,343 works
Cite
Cite as Rickard Stureborg, Dimitris Alikaniotis and Yoshi Suhara. 2024. Large Language Models are Inconsistent and Biased Evaluators. arXiv:2405.01724.
@misc{stureborg2024large,
title = {{Large Language Models are Inconsistent and Biased Evaluators}},
author = {Rickard Stureborg, Dimitris Alikaniotis and Yoshi Suhara},
year = {2024},
doi = {10.48550/arxiv.2405.01724},
eprint = {2405.01724},
archivePrefix = {arXiv},
url = {https://doi.org/10.48550/arxiv.2405.01724}
}References
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