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LLM evaluation confidence intervals are too narrow due to clustered data

A common assumption in evaluating language models is that each test example is independent, but this is often violated in practice. When examples are clustered (e.g., multiple questions from the same document or turns from the same conversation), they carry overlapping information, leading to confidence intervals that are narrower than they should be. This statistical bias can cause researchers to falsely believe they have achieved significant improvements when they have not. The solution involves resampling entire clusters rather than individual examples to accurately reflect the effective sample size and correct the confidence interval width. AI

IMPACT Highlights a critical flaw in common LLM evaluation practices, potentially invalidating past benchmark results and requiring re-evaluation of model improvements.

RANK_REASON The item discusses a statistical methodology for evaluating language models, including a formula and code example for correction. [lever_c_demoted from research: ic=1 ai=1.0]

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LLM evaluation confidence intervals are too narrow due to clustered data

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

    Your eval's confidence interval assumes independent examples. Yours are clustered.

    <p>Every binomial confidence interval you have ever computed on an eval pass rate, Wald, Wilson, Clopper-Pearson, all of them, rests on one assumption: each example is an independent draw. Most eval sets violate it. You have 40 questions generated from the same 8 documents, or 20…