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arXiv 2311.07466cs.CLcs.AIcs.LG

关于衡量自然语言解释的忠实性或自洽性

On Measuring Faithfulness or Self-consistency of Natural Language Explanations

Heidelberg University(海德堡大学)

Letitia Parcalabescu, Anette Frank

AI总结:

本文指出现有LLM解释忠实性测试实际衡量输出自洽性,提出细粒度度量CC-SHAP并构建比较一致性库,以更接近模型内部的方式推进忠实性衡量。

摘要:

大型语言模型(LLM)可以通过事后(post-hoc)或思维链(Chain-of-Thought,CoT)解释来阐述其预测。但LLM可能会编造出听起来合理却与其底层推理不忠实的解释。近期研究设计了旨在评判事后或CoT解释忠实性的测试。在本文中,我们认为这些忠实性测试衡量的并非模型内部运作的忠实性,而是其输出层面的自洽性。我们的贡献有三点:i) 我们澄清了忠实性测试在模型可解释性方面的地位,将其定性为自洽性测试。这一评估通过ii) 构建一个用于自洽性测试的比较一致性库(Comparative Consistency Bank)来加以强调,该库首次在包含11个开源LLM和5项任务的通用套件上比较了现有测试——包括iii) 我们新的自洽性度量CC-SHAP。CC-SHAP是一种细粒度的LLM自洽性度量(而非测试)。它比较模型的输入如何分别贡献于预测答案和生成解释。我们的细粒度CC-SHAP度量使我们能够iii) 比较LLM在做出预测时的行为,并在更深层次上分析其他一致性测试的效果,这使我们比严格面向表面输出的测试更接近模型内部,从而向衡量忠实性迈进了一步。我们的代码可在\url{https://github.com/Heidelberg-NLP/CC-SHAP}获取。

英文摘要:

Large language models (LLMs) can explain their predictions through post-hoc or Chain-of-Thought (CoT) explanations. But an LLM could make up reasonably sounding explanations that are unfaithful to its underlying reasoning. Recent work has designed tests that aim to judge the faithfulness of post-hoc or CoT explanations. In this work we argue that these faithfulness tests do not measure faithfulness to the models' inner workings -- but rather their self-consistency at output level. Our contributions are three-fold: i) We clarify the status of faithfulness tests in view of model explainability, characterising them as self-consistency tests instead. This assessment we underline by ii) constructing a Comparative Consistency Bank for self-consistency tests that for the first time compares existing tests on a common suite of 11 open LLMs and 5 tasks -- including iii) our new self-consistency measure CC-SHAP. CC-SHAP is a fine-grained measure (not a test) of LLM self-consistency. It compares how a model's input contributes to the predicted answer and to generating the explanation. Our fine-grained CC-SHAP metric allows us iii) to compare LLM behaviour when making predictions and to analyse the effect of other consistency tests at a deeper level, which takes us one step further towards measuring faithfulness by bringing us closer to the internals of the model than strictly surface output-oriented tests. Our code is available at \url{https://github.com/Heidelberg-NLP/CC-SHAP}

机构、总结、中文摘要均由AI分析而来,可能存在错误,请以论文正文为准。

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