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LLM evaluation metrics 'acc' vs 'acc_norm' explained

A technical discussion highlights the 'acc vs acc_norm' problem in evaluating Large Language Models (LLMs), particularly in multiple-choice tasks. The standard accuracy metric (acc) favors shorter answers due to its reliance on summed log-likelihood, which is inherently penalized by answer length. The normalized accuracy metric (acc_norm) attempts to correct this by dividing the score by the byte length of the continuation, aiming for a more consistent comparison across models and tokenizers. However, acc_norm can also introduce biases, such as favoring answers that split into many predictable subwords. The article suggests reporting both metrics and choosing one consistently per task family before training to avoid misleading evaluations. AI

IMPACT Clarifies potential biases in LLM evaluation metrics, guiding researchers toward more accurate model comparisons.

RANK_REASON Technical paper discussing LLM evaluation metrics. [lever_c_demoted from research: ic=1 ai=1.0]

Read on dev.to — LLM tag →

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LLM evaluation metrics 'acc' vs 'acc_norm' explained

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  1. dev.to — LLM tag TIER_1 English(EN) · jidonglab ·

    acc vs acc_norm: Why Length Bias Skews LLM Eval Scores

    <p>Your fine-tune gains three points of <code>acc_norm</code> on HellaSwag and loses two points of <code>acc</code>. Same checkpoint, same harness, same seed. Nothing about the model's commonsense reasoning moved in two directions at once — you changed its average per-token entro…