Graduating the Benchmark Scale: Lessons from Thermometry
Paper · 2026 · Sean Trott and Oisín Parkinson-Coombs
Summary
This position paper from the EvalEval 2026 workshop looks at a neglected part of LLM benchmark validity. It asks whether a benchmark score can be treated as a graded measure of an underlying capability, and what justifies reading equal score gaps as equal differences in ability. The authors frame this with Hasok Chang's "problem of nomic measurement" from the history of thermometry. The problem is that the function linking an observable reading to a hidden quantity cannot be tested without already knowing that quantity.
The paper introduces no new data or models. Instead, it compares hypothetical score-to-capability mappings. It then shows how thermometry escaped this circularity through epistemic iteration: step-by-step, mutually correcting refinement of instruments, fixed points and theory. LLM capabilities are more abstract and lack stable anchors, so the analogy only partly holds.
The central claim is that the problem's severity depends on what a benchmark is for. Because the assumed mapping can change deployment and regulatory choices, researchers should state their goals and theoretical commitments explicitly.
Key points
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Figure 1 sketches six possible links between measured and "true" capability: null, linear, categorical, logarithmic, sigmoidal and exponential.
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The authors illustrate the issue with an imagined 100-item Python benchmark. A jump from 30 to 50 and a jump from 50 to 70 mean the same thing only under a linear mapping. A logarithmic mapping makes the first gap larger, and an exponential one makes the second gap larger.
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Chang (2004) describes three stages in thermometry:
- bodily sensation;
- ordinal thermoscopes;
- numerical thermometers built on fixed points and instrument comparison, with Henri Regnault's work on air thermometers as the example.
Along the way, the boiling point of water was later replaced by steam temperature as a fixed point.
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Three benchmark goals are distinguished:
- ranking models, which works under every mapping except null;
- detecting a behavior, which needs a meaningful threshold;
- measuring degrees of a capability, where the problem is hardest.
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Human baselines (METR, 2026) are suggested as possible anchors. However, they are judged less stable than physical fixed points and may not be comparable with LLM behavior.
Institutions
Fields, topics and concepts
📚 Shelves 8The field of science this work belongs to (OpenAlex fields).Computer Science · 18,614 worksArtificial Intelligence · 17,965 worksArts and Humanities · 17,450 worksLanguage and Linguistics · 17,296 worksSocial Sciences · 1,954 worksSafety Research · 626 worksDecision Sciences · 249 worksManagement Science and Operations Research · 134 works
🧭 Topics 1Research subjects and languages the work is about.Evaluation & benchmarks · 1,341 works
Cite
Cite as Sean Trott and Oisín Parkinson-Coombs. 2026. Graduating the Benchmark Scale: Lessons from Thermometry. Proceedings of the Workshop on Evaluating Evaluations (EvalEval).
@inproceedings{trott2026graduating,
title = {{Graduating the Benchmark Scale: Lessons from Thermometry}},
author = {Sean Trott and Oisín Parkinson-Coombs},
booktitle = {Proceedings of the Workshop on Evaluating Evaluations (EvalEval)},
year = {2026},
doi = {10.18653/v1/2026.evaleval-1.21},
url = {https://doi.org/10.18653/v1/2026.evaleval-1.21}
}References
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