What is inter-rater reliability, and why is it important in LLM evaluation?

Inter-rater reliability (IRR) measures the degree of agreement among different evaluators assessing the same outputs from an LLM. It is crucial in LLM evaluation because stakeholder interpretation can vary, affecting perceived output quality. High IRR indicates that evaluators share similar judgments, suggesting the evaluation process is reliable and valid. This minimizes bias and enhances the credibility of evaluation results. To compute IRR, statistical methods like Cohen's Kappa or Fleiss' Kappa can be used, especially when assessing subjective outputs where human judgment is involved.