On the Statistical Significance with Relevance Assessments of Large Language Models

Test collections are an integral part of Information Retrieval (IR) research. They allow researchers to evaluate and compare ranking algorithms in a quick, easy and reproducible way. However, constructing these datasets requires great efforts in manual labelling and logistics, and having only few human relevance judgements can introduce biases in the comparison. Recent research has explored the use of Large Language Models (LLMs) for labelling the relevance of documents for building new retrieval test collections. Their strong text-understanding capabilities and low cost compared to human-made judgements makes them an appealing tool for gathering relevance judgements. Results suggest that LLM-generated labels are promising for IR evaluation in terms of ranking correlation, but nothing is said about the implications in terms of statistical significance. In this work, we look at how LLM-generated judgements preserve the same pairwise significance evaluation as human judgements. Our results show that LLM judgements detect most of the significant differences while maintaining acceptable numbers of false positives. However, we also show that some systems are treated differently under LLM-generated labels, suggesting that evaluation with LLM judgements might not be entirely fair. Our work represents a step forward in the evaluation of statistical testing results provided by LLM judgements. We hope that this will serve as a basis for other researchers to develop reliable models for automatic relevance assessments.

How Discriminative Are Your Qrels? How To Study the Statistical Significance of Document Adjudication Methods

Creating test collections for offline retrieval evaluation requires human effort to judge documents' relevance. This expensive activity motivated much work in developing methods for constructing benchmarks with fewer assessment costs. In this respect, adjudication methods actively decide both which documents and the order in which experts review them, in order to better exploit the assessment budget or to lower it. Researchers evaluate the quality of those methods by measuring the correlation between the known gold ranking of systems under the full collection and the observed ranking of systems under the lower-cost one. This traditional analysis ignores whether and how the low-cost judgements impact on the statistically significant differences among systems with respect to the full collection. We fill this void by proposing a novel methodology to evaluate how the low-cost adjudication methods preserve the pairwise significant differences between systems as the full collection. In other terms, while traditional approaches look for stability in answering the question "is system A better than system B?", our proposed approach looks for stability in answering the question "is system A significantly better than system B?", which is the ultimate questions researchers need to answer to guarantee the generalisability of their results. Among other results, we found that the best methods in terms of ranking of systems correlation do not always match those preserving statistical significance.