REVIEW 3 major objections 5 minor 2 cited by
Large language models can report two orders of uncertainty at once when asked for probability intervals instead of a single confidence score, and the resulting scores better detect both wrong answers and ambiguous questions.
Reviewed by Pith at T0; open to challenge. T0 means a machine referee read the full paper against a public rubric. the ladder, T0–T4 →
2026-08-02 18:25 UTC pith:U2PTRFAX
load-bearing objection Good idea, honest experiments, but the semantic validity of the elicited intervals is the crux and remains untested. the 3 major comments →
Verbalizing LLM's Higher-order Uncertainty via Imprecise Probabilities
The pith
A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.
Core claim
Verbalized uncertainty need not be a point estimate. The paper introduces prompts that elicit, for each candidate answer, a lower probability (the smallest value the model considers plausible) and an upper probability (the largest value it considers defensible), plus two alternatives: a credal set built from disagreement across an ensemble of models or seeded runs, and a possibility function that allows 'none of the above.' These representations are post-processed into a scalar second-order uncertainty score via the maximum mean imprecision (MMI), computed as an interval width for a single answer or an upper bound over the candidate set. The central empirical claim is that this interval-base
What carries the argument
Probability interval: per-answer lower/upper probabilities, where the lower bound is the smallest probability the model calls plausible and the upper bound the largest it calls defensible; the interval width is the second-order uncertainty. Credal set: a collection (convex hull) of precise probability distributions from an ensemble or multiple seeded runs, whose pointwise min/max form lower/upper bounds. Possibility function: a non-additive score on candidate answers, normalized so at least one answer has plausibility 1, allowing 'none of the above' without redistributing mass. MMI: the largest gap between upper and lower probability over any event, approximated by the interval width for a s
Load-bearing premise
The load-bearing premise—flagged as unverifiable in the paper's own limitation section—is that the numeric lower and upper bounds an LLM gives are meaningful approximations of its actual beliefs rather than arbitrary prompt-driven slack, and that the model interprets the probability prompts as intended; without this, the observed separation of first- and second-order uncertainty is an artifact of the prompt.
What would settle it
Collect items with known correctness, elicit lower/upper probabilities, and check whether the empirical frequency of a correct answer across items whose reported lower probability is at or above a threshold t stays above t; systematic violations would show the interval does not bound the model's beliefs. A sharper form: offer the model bets priced inside its stated interval and check whether it accepts a combination that guarantees a loss.
If this is right
- Interval-based uncertainty scores can replace sampling-based estimates in error and ambiguity detection: on QA benchmarks, ProbInt, Credal, and Pos rank among the best methods while costing about the same as simple verbalized confidence for ProbInt and Pos.
- If the interval representation is faithful, downstream systems can use interval width as an abstention or clarification signal, since width is supposed to track reducible second-order uncertainty.
- Because the transition from point to interval only changes the prompt and adds a cheap post-processing step (MMI), the approach works on closed, API-only models with no access to internal probabilities.
- The alignment of LLM answer selection with the maximin rule over lower probabilities provides a concrete decision-theoretic criterion for when to distrust a model's stated pick.
Where Pith is reading between the lines
- If the lower/upper probabilities are semantically meaningful, one can validate them independently with a sure-loss test: offering bets at the stated bounds and checking whether the model ever accepts a combination that guarantees a loss. The paper does not run this test.
- A natural extension beyond QA is to use interval width as an acquisition function in active learning or an early-stopping signal in agentic loops; the cost is low enough that such uses are plausible, but the paper does not demonstrate them.
- The possibility function's explicit 'none of the above' score suggests a diagnostic for open-vocabulary hallucination: a high score for a non-listed answer would reveal an incomplete candidate set, a test the paper does not perform.
- The synthetic in-context-learning results imply a sharper prediction: adding in-context examples should narrow the reported intervals monotonically for a given task rule, which could be checked across rule families and would separate genuine belief revision from prompt artifacts.
Editorial analysis
A structured set of objections, weighed in public.
Referee Report
Summary. This paper proposes replacing point-valued verbalized uncertainty in LLMs with imprecise probability representations: lower/upper probability intervals (ProbInt), credal sets (Credal), and possibility functions (Pos), together with a DeFinetti-style betting-price prompt. The authors introduce prompting procedures and use Maximum Mean Imprecision (MMI) to summarize second-order uncertainty. They evaluate on synthetic sequence-transformation tasks with controlled ambiguity noise p and ICL example count m, and on MAQA, AmbigQA, and MMLU-Pro. They report that IP-based scores stay flat under first-order noise, track error as ICL examples grow, improve AUROC for ambiguity and correctness detection, align with the LLM's own choices under maximin, and incur low API cost. The central claim is that this framework elicits and disentangles first- and second-order uncertainty more faithfully than vanilla confidence.
Significance. If the claims hold, the paper would be a useful contribution: it connects a mature decision-theoretic framework (imprecise probabilities) to black-box verbalized LLM uncertainty, and the proposed prompts are simple and deployment-relevant. The DeFinetti prompt is a principled attempt to ground probabilities in betting behavior, and the possibility-function treatment of "none of the above" is a nice idea. The cost comparison is practical. However, the support is uneven in two load-bearing places: the synthetic disentanglement experiment largely restates the data-generation definitions, and the semantic meaningfulness of the elicited intervals is asserted rather than validated. The AUROC improvements are consistent but lack significance testing, and could in principle be produced by any informed monotone width-based score. The paper is worth publishing if the authors add an independent validity check and temper the claims accordingly.
major comments (3)
- [§4, Figs. 6–7] The synthetic experiment validates the method against the paper's own definitions: p is labelled first-order and m second-order by construction ("We treat the ambiguity noise p as the first-order because |Y*|>1, and the number of in-context examples m controls the second-order"). Showing that PROBINT is flat in p and decreases in m is consistent with the construction but does not independently confirm that the method separates the two latent quantities in the model's beliefs. A method that responds arbitrarily to prompt wording could produce the same plots. Please add a validation in which the two uncertainty sources are not definitionally tied to the experimental manipulation, e.g., fix p and vary model confidence through a separate channel, or compare against an independent behavioral measure of second-order uncertainty (repeated sampling, clarification ensembles).
- [§3.2, Eq. (2), and §6] The central premise is that the lower/upper probabilities elicited by Prompt 2 are meaningful degrees of belief. The paper states this directly in §6: "we assume verbalized uncertainty is approximately rational; although allowing imprecision mitigates, this cannot be fully verified." No independent test anchors the interval endpoints. Because the MMI score is computed from the lower probabilities (Eq. 2: MMI ≤ 1 − Σ p(y)), an arbitrary downward shift in lower probabilities would inflate second-order uncertainty without changing any behavior. The AUROC gains in Table 1 and the maximin alignment in Fig. 14 could be produced by any monotone width-based heuristic. I request an external validity check: e.g., verify that vanilla point probabilities fall inside elicited intervals on average; elicit betting prices for the same events and test coherence; or evaluate interval forecasts with a prop
- [§5, Table 1] I cannot assess whether the reported improvements are statistically reliable. The paper gives means and standard deviations over five repetitions, but no paired significance tests or effect sizes. For several GPT-5 cells the proposed methods are within one standard deviation of VANILLA (e.g., MMLU-Pro: PROBINT 0.8617±0.0082 vs VANILLA 0.8587±0.0192; Non-AmbigQA: PROBINT 0.7713±0.0044 is numerically below VANILLA 0.7756±0.0138). The "Avg. Rank" column aggregates six cells and does not account for variability. Please add paired bootstrap or Wilcoxon tests, either across the six dataset-model pairs or at the item level, and identify which comparisons are significant.
minor comments (5)
- [Abstract; throughout] Typo "repesenting" in the abstract; the method name is rendered inconsistently as "De Finetti", "DEFINETTI", and "DeFinetti". Please standardize.
- [Alg. 1, Alg. 2] Algorithms 1 and 2 have no iteration bound; if the model never satisfies the verifier, the loop does not terminate. Also, the text says the IMPRECISE-PROBABILITY verifier checks both sum lower ≤ 1 and sum upper ≥ 1, but immediately adds that only constraint (i) is verified. Please clarify the actual verification procedure.
- [§5.1, Fig. 10] The multiplicative combination DeFinetti × IP is introduced ad hoc ("to achieve scale invariance"). Please provide a justification or a sensitivity analysis over alternative aggregation rules (sum, min, product).
- [§5, Task definition] For ambiguous items, correctness is judged only against a single reference y*, so a valid alternative answer in Y* is counted as incorrect. This may conflate ambiguity with incorrectness; please state this explicitly as an evaluation choice and discuss its effect on the reported AUROC.
- [Appendix D] In D.2.1 the ground-truth AU/EU decomposition uses cross-entropy and KL proxies from corpus statistics. The paper treats these as "ground truth"; please make clear that these are proxies and that concordance is with the proxy, not with the true latent uncertainty.
Circularity Check
No significant circularity; the derivation is empirical and the main assumptions are stated as limitations.
full rationale
The paper's central claims are empirical rather than first-principles derivations. PROBINT's second-order score is computed directly from LLM-verbalized lower probabilities after a coherence verifier; Eq. (2) is an algebraic identity for any lower probability, not a fitted quantity. The synthetic experiments in §4 stipulate p as first-order and m as second-order, but the observed flatness under p and monotonicity under m are not mathematically forced by the score definition; they are behavioral results of the model and therefore constitute genuine empirical tests. Real-world evaluations use external labels (MAQA, AmbigQA, MMLU-Pro) and a corpus-based KL proxy, so the reported AUROC improvements are not constructed from the method's own outputs. The MMI metric is cited from prior work by overlapping authors (Chau et al. 2025, 2026), but the paper states the relevant formulas directly and the upper bound is elementary; the imprecision interpretation is standard in imprecise-probability literature. Section 6 explicitly admits the load-bearing assumption that verbalized uncertainty is approximately rational and cannot be fully verified; that is a limitation on semantic validity of the elicited intervals, not a circular derivation. No step reduces to its inputs by construction, and no fitted parameter is relabeled as a prediction.
Axiom & Free-Parameter Ledger
free parameters (3)
- Number of CREDAL ensemble members / samples =
5
- Multiplicative combination DeFinetti × IP (Fig. 10)
- MMI upper-bound substitution =
1 − Σ p(y)
axioms (5)
- domain assumption Verbalized uncertainty is approximately rational
- domain assumption The model correctly interprets the prompting semantics (lower = smallest plausible, upper = largest defensible)
- standard math De Finetti coherence: fair betting prices must satisfy the probability axioms
- domain assumption KL(p⋆ ∥ p̂) is a valid proxy for ground-truth second-order uncertainty
- ad hoc to paper In the synthetic experiment, ambiguity noise p is first-order and #ICL examples m is second-order
Cite this review
Pith. "Pith review of Verbalizing LLM's Higher-order Uncertainty via Imprecise Probabilities." pith.science (2026). https://pith.science/paper/U2PTRFAX
@misc{pith2026260310396,
author = {Pith},
title = {Pith review of: Verbalizing LLM's Higher-order Uncertainty via Imprecise Probabilities},
year = {2026},
howpublished = {\url{https://pith.science/paper/U2PTRFAX}},
note = {Machine review of arXiv:2603.10396}
}
read the original abstract
Despite the growing demand for eliciting uncertainty from large language models (LLMs), empirical evidence suggests that LLM behavior is not always adequately captured by the elicitation techniques developed under the classical probabilistic uncertainty framework. This mismatch leads to systematic failure modes, particularly in settings that involve ambiguous question-answering, in-context learning, and self-reflection. To address this, we propose novel prompt-based uncertainty elicitation techniques grounded in \emph{imprecise probabilities}, a principled framework for repesenting and eliciting higher-order uncertainty. Here, first-order uncertainty captures uncertainty over possible responses to a prompt, while second-order uncertainty (uncertainty about uncertainty) quantifies indeterminacy in the underlying probability model itself. We introduce general-purpose prompting and post-processing procedures to directly elicit and quantify both orders of uncertainty, and demonstrate their effectiveness across diverse settings. Our approach enables more faithful uncertainty reporting from LLMs, improving credibility and supporting downstream decision-making.
Figures
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This paper was first reviewed by deepseek-v4-flash on August 2, 2026.
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