arXiv · 2609.26776
Birnbaum's principles in Venn diagrams: Extended version with Lean verification
Abstract
Birnbaum's theorem states that the sufficiency and conditionality principles jointly imply, and are implied by, the likelihood principle. To enable formal certification of the results in Lean, we make the conditionality relation explicit through a finite-sample formulation based on \cite{Evans2013}. We reformulate the theorem as a statement about classes of statistical procedures that preserve statistical relations, and show that the proof reduces to the propagation of evidential equality along chains of conditionality-related inference bases (experiment--observation pairs). The main results are illustrated by Venn diagrams, and a worked finite example exhibits two pairs of inference bases: one related by conditionality but not by sufficiency, and the other related by sufficiency but not by conditionality. For finite parameter spaces with at least two points, the class of likelihood-invariant procedures with codomain $[0,1]$ is strictly contained in the class of sufficiency-invariant procedures.
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Jaime Enrique Lincovil Curivil, Alexandre Galvão Patriota. 2026-09-22. Birnbaum's principles in Venn diagrams: Extended version with Lean verification. https://arxiv.org/abs/2609.26776
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