Stop Evaluating Models Like It's the 50s - Alejandro Vidal, Mindmakers
Jul 13, 2026 · 23:35
Alejandro Vidal of Mindmakers argues that counting correct answers in LLM benchmarks—classical test theory—should be replaced by item response theory (IRT) from psychometrics for richer evaluations. Using real data from Epoch.ai, he shows that while Claude Opus 4.1 scored 245 right and Gemini 3 Pro 247, IRT reveals Gemini is nearly one standard deviation more intelligent because it answers harder questions. IRT assigns each item difficulty (B) and discrimination (A), enabling benchmark auditing—Vidal flagged mislabeled items like a question about passengers whose gold answer was actually total people killed. He demonstrates reducing a 484-item benchmark to 97 items with 99% ranking correlation by selecting high-discrimination items, saving tokens and money. IRT also detects contamination via unexpected residuals, protects benchmarks through adaptive testing with unique fingerprint sets, and identifies model families (e.g., DeepSeek distillations correlate 0.38). Vidal previews future extensions like multidimensional models and alignment measurement.
