Agreement Metrics for LLM-as-Judge Evaluation: What to Report and Why
arXiv:2606.00093v1 Announce Type: cross Abstract: Validating an LLM judge against human annotations usually means reporting several agreement statistics: accuracy, precision, recall, $F_1$, Cohen's $\kappa$, and one or more rank correlations. A survey of 24 recent LLM-as-judge papers finds metric choice entangled with the judgment scale, tie handling, invalid outputs, and abstention handling, and those choices rarely stated. For binary criteria -- the common case in rubric-based evaluation, where each criterion is graded MET or UNMET -- most of the reported numbers are redundant: Pearson's $r$, Spearman's $\rho$, Kendall's $\tau_b$, the phi coefficient $\phi$, and the Matthews Correlation Coefficient all reduce to a single number on non-degenerate binary data, so reporting several of them only creates an illusion of corroborating evidence. Cohen's $\kappa$ is the one agreement coefficient that adds information: it shares $\phi$'s numerator but normalizes differently, and the gap betwee