REVIEW 3 major objections 4 minor 40 references
Learned linear aggregation of 15 language models' forecasts beats every individual model and all classical rules, with the gain traced to error-pattern diversity; training-cutoff contamination inflates apparent model rankings.
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 12:59 UTC pith:QXY54JEB
load-bearing objection Learned aggregation of LLM forecasts works out-of-sample and the contamination analysis is valuable, but the symbolic-regression evidence for the diversity mechanism is partially in-sample and needs a corrected evaluation. the 3 major comments →
Wisdom of LLM Crowds: Aggregation and Contamination in Language Model Ensembles
The pith
A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.
Core claim
On a set of 94 prediction questions that resolve after every model's training cutoff, both learned aggregators—a multilayer perceptron and a logistic regression—beat all 15 individual models and all classical aggregators, with the linear model matching the nonlinear one. This near-equivalence, together with the symbolic-regression finding that the network's mapping collapses to a two-model contrastive formula, leads the author to conclude that the aggregation benefit is carried by error-pattern diversity: the learned weights track how independent a model's errors are from the rest of the crowd, not how accurate the model is. The same diversity mechanism is what has been documented in human c
What carries the argument
The central machinery is a 'temporal transfer' evaluation design: the learned aggregators (an MLP and an L2-regularized logistic regression) are trained on 160 questions that resolve before all models' cutoffs and tested on 94 questions that resolve after them, so the test questions are genuinely novel. The paper's main interpretive tool is symbolic regression, which distills the trained MLP's input-output map into interpretable formulas; the lowest-complexity useful formula on the Pareto frontier is a logistic transform of the difference between two models' probability estimates, a pure disagreement signal. A coefficient analysis of the logistic regression completes the machinery, showing t
Load-bearing premise
The clean-subset evaluation of the recovered two-model formula is not fully out-of-sample: the formula was distilled from an MLP trained on 196 items, 48 of which are also in the 94-item clean set, so those 48 clean scores may reflect indirect fitting to ground truth.
What would settle it
Recompute the Brier score of the two-model contrastive formula on only the 46 clean items that are not in the 208-item training set; if the formula's advantage over the arithmetic mean disappears on that disjoint subset, the symbolic-regression evidence for the diversity mechanism is nullified.
If this is right
- If the diversity mechanism is real, then a simple linear reweighting of model outputs is sufficient to harvest most of the wisdom of an LLM crowd; elaborate nonlinear ensembles add little.
- Any evaluation of LLM forecasting on resolved events must control for training-cutoff contamination; otherwise published capability gaps and model rankings are systematically distorted.
- LLM crowds can match or beat their best individual member, so ensemble forecasting with diverse models is a viable, scalable alternative to single-model systems.
- The persistence of a roughly twofold Brier-score gap against a dynamically updated market, even at matched cutoffs, sets a clear target: frozen-snapshot LLMs lack real-time information aggregation, so the ceiling is structural rather than an artifact.
Where Pith is reading between the lines
- Testable extension: an explicitly diversity-weighted linear aggregator, with weights proportional to measured error decorrelation and no learned parameters, should reproduce much of the MLP's gain; if it does not, the linearity story is incomplete.
- If contamination distorts rankings this much, the same mechanism likely affects other benchmark comparisons on dated event data; re-running such evaluations on post-cutoff items could shrink reported capability gaps elsewhere.
- The U-shaped model selection (strong cloud plus weak local models) suggests an ensemble design rule: inject deliberately worse but decorrelated models rather than only the best performers; this is implicit in the paper but a prospective test would harden the claim.
- A deliberation protocol in which models observe each other's estimates could narrow the gap to dynamic markets, but the cutoff-matched result implies a residual gap would remain because no fixed training snapshot can incorporate new information.
Editorial analysis
A structured set of objections, weighed in public.
Referee Report
Summary. The paper reports an experiment in which probability estimates on 254 binary prediction-market questions are elicited from 15 LLMs, and four classical aggregators (arithmetic mean, median, geometric/log-odds mean, harmonic mean) are compared with two learned aggregators (L2-regularized logistic regression and a two-hidden-layer MLP). The learned aggregators are trained on 160 items resolving before 1 September 2025 and evaluated on a 94-item 'clean' subset resolving after that date, a genuine temporal-transfer design. The paper's central claims are that the learned aggregators outperform all individual models and all classical aggregators; that logistic regression performs comparably to the MLP, implying the benefit comes from a linear combination of diverse outputs; that symbolic regression recovers a simple disagreement formula σ(p_GeminiPro − p_ClaudeHaiku) that nearly replicates the learned-aggregation benefit; and that training-cutoff contamination substantially inflates apparent model performance and distorts model rankings, with the cloud--local gap collapsing from 35.8% to 8.9% on clean items.
Significance. If the claims hold, the paper makes a meaningful contribution to both collective-intelligence research and LLM evaluation methodology. The temporal-transfer design for the learned aggregators is a real strength: it avoids the circularity that would arise if aggregators were trained and tested on the same items. The contamination analyses are thoughtful and include useful robustness checks (cutoff-date perturbations and a nested clean subset). The supplementary materials appear to ship code and data, which is welcome. However, two load-bearing points currently outrun the evidence: the claim that learned aggregators beat every individual model is not backed by explicit clean-subset individual scores, and the symbolic-regression clean-subset evaluation is partially in-sample. Both are fixable, so I view this as a major-revision rather than a rejection.
major comments (3)
- [§3.1, Fig. 2] The central claim that the learned aggregators 'achieved lower Brier scores than all individual models and all classical aggregators' (§4.1, also the abstract) is not directly supported by the numerical results presented. Table 2 reports individual Brier scores only on the full 208-item dataset; the right panel of Fig. 2 shows clean-subset individual scores visually but gives no numerical values. The reader therefore cannot verify, e.g., that the MLP's BS=0.264 and logistic regression's BS=0.241 are actually below the best clean-subset individual model. Please add a table reporting Brier, accuracy, and AUC for all 15 models, the four classical aggregators, and the two learned aggregators on the 94-item clean subset, together with paired tests (e.g., bootstrap or Wilcoxon) comparing each learned aggregator against the best individual model. This is necessary to support the paper's headlin
- [§2.5, §3.3] The symbolic-regression clean-subset score is partially in-sample. Section 2.5 states that the MLP distilled by SR was retrained on all complete rows of the full 208-item dataset (n=196) with ground-truth labels, and SR searched for formulas minimizing MSE against this MLP on those same 196 items. The 94-item clean subset includes 48 items drawn from the original 208-item dataset (Section 2.1), so for those 48 items the MLP's predictions—and hence the SR formula fitted to them—are indirectly fitted to the ground-truth outcomes. Scoring the recovered formula on the 94-item clean subset is therefore not an out-of-sample test for 48 of the 94 items. The paper's defense in Section 2.5 that 'ground truth enters at the evaluation stage instead' does not address this overlap, because ground-truth labels were used to train the MLP on exactly those items. Please re-run the SR evaluation on the 46
- [§3.1, §4.1] The core finding that 'a linear model performs comparably to the nonlinear model' is not statistically assessed. The paper reports that logistic regression has a lower Brier score (0.241 vs. 0.264) while the MLP has better AUC (0.657 vs. 0.633) and accuracy (0.606 vs. 0.574), but no test quantifies whether these differences are consistent or whether the two learned aggregators are statistically distinguishable. Additionally, the logistic regression's Brier advantage over the arithmetic mean is not item-consistent: the sign test is far from significant (46/94, p=.837) and the Wilcoxon test is not significant (p=.122); only the permutation test (p=.002) supports the mean reduction. The paper does discuss this pattern, but the linear-vs-nonlinear conclusion in Section 4.1 is stated more firmly than the inferential evidence warrants. Please provide confidence intervals or paired tests for LR
minor comments (4)
- [§3.1 vs. §3.3] The arithmetic-mean Brier score on the clean subset is reported as 0.313 in Section 3.1, but Section 3.3 gives the symbolic-regression formula's clean-subset score as 0.243 without an explicit comparison to the arithmetic mean on the same 94 items. The text also states that the formula achieves BS=0.231 on 203 full-dataset items against arithmetic-mean 0.265. Please add an explicit clean-subset comparison (0.243 vs. 0.313, if that is the correct pairing) so the reader does not have to infer it from different subsets.
- [Fig. 1 caption] The caption says no bootstrap brackets are drawn for the learned aggregators because 'their temporal transfer evaluation design is not comparable to the all-data bootstrap used for other methods.' This is a reasonable caveat, but the main text and figure would benefit from stating that the point comparisons in the figure are not uncertainty-adjusted; otherwise the visual impression of a large gap is stronger than the statistical evidence.
- [§2.5] The sentence 'Ground truth enters at the evaluation stage instead' is at best incomplete, because the MLP is trained with binary cross-entropy against ground-truth outcomes on the same items used for SR distillation. Please rephrase to acknowledge the overlap and to make clear which reported scores are out-of-sample and which are not.
- [§3.3, Table 5] The relationship between the 'model selection frequencies' in Table 5 and the recovery of the specific formula σ(p_GeminiPro − p_ClaudeHaiku) is not fully explained. Does the selection frequency refer to variables appearing in Pareto-frontier formulas, or to the specific lowest-complexity formula? Please clarify the connection, since the stability of the two-variable formula across runs is what supports the mechanistic reading.
Circularity Check
Symbolic-regression clean-subset Brier is partly in-sample; core aggregation result remains out-of-sample.
specific steps
-
fitted input called prediction
[Section 2.5 (Symbolic regression) and Section 3.3 (Symbolic regression results)]
"we retrained the MLP on all complete rows of the full 208-item dataset (n = 196; here, no imputation is applied, so the 12 rows containing a missing cell are dropped) rather than on the 160 non-clean items used for the temporal transfer evaluation. ... Ground truth enters at the evaluation stage instead: any formula recovered by SR is subsequently scored against the actual resolutions, on both the full dataset and the clean subset (Sect. 3.3), so no performance claim in this paper rests on a formula's agreement with the MLP."
The clean subset is not disjoint from the SR training set: Section 2.1 says 'Of the 208 items in the main dataset, 48 resolved after this date' and the 94-item clean subset is formed by supplementing those 48 with 46 new items. Section 2.5 retrains the MLP on all complete rows of the same 208-item dataset, so those 48 items are in the MLP's training set. The SR formula is fit to the MLP's predictions on exactly those training rows; the MLP's predictions on training rows are fit to the ground-truth resolutions via binary cross-entropy. Therefore scoring the recovered formula on the clean subset (BS = 0.243) is an indirect in-sample evaluation for 48 of the 94 items, not an out-of-sample prediction for them. The paper's statement that 'ground truth enters at the evaluation stage instead' is
full rationale
The learned-aggregation core result is genuinely out-of-sample: the MLP and logistic regression were trained on the 160 non-clean items and evaluated on the 94 clean items, so their Brier/accuracy/AUC advantage over individuals and classical aggregators is not circular. The linear-vs-nonlinear comparison is likewise based on the same temporal-transfer evaluation. The symbolic-regression analysis, however, contains a partial in-sample evaluation: the SR-target MLP was retrained on the full 208-item dataset, which includes 48 of the 94 clean items, and the recovered formula is then scored on those same clean items. For those 48 items, the formula's clean-subset Brier is inherited from the MLP's training fit to ground truth. This weakens the '0.243 on clean subset' quantification and the diversity-mechanism support drawn from it. The mechanism claim retains independent support from the logistic-regression weight analysis, which correlates weights trained on 160 non-clean items with error-decorrelation measured on the 94 clean items, and from the SR selection-frequency pattern (though that pattern is itself based on the full contaminated dataset). Self-citations to Douven et al. [15,16] are methodological or interpretational and not load-bearing; no uniqueness theorem or ansatz is smuggled in via citation. Net: one partially constructed 'prediction' in a supporting analysis; the central aggregation result is independent.
Axiom & Free-Parameter Ledger
free parameters (5)
- Logistic regression L2 penalty λ =
0.01
- MLP hyperparameters (hidden units 64/32, dropout 0.2, learning rate 5e-3, epochs 25, batch size 16) =
64/32, 0.2, 5e-3, 25, 16
- Minimum trader threshold for market selection =
75
- Clean subset cutoff date =
2025-09-01
- Symbolic regression complexity penalty / Pareto-frontier selection =
unspecified
axioms (4)
- domain assumption Training cutoff dates from official documentation are accurate at month granularity.
- domain assumption Manifold Markets play-money probabilities are well-calibrated and comparable to real-money markets.
- domain assumption Mean pairwise correlation of squared errors is a valid operationalization of error-pattern diversity.
- domain assumption The temporal-transfer design (training on 160 contaminated items, evaluating on 94 clean items) is a fair test of learned aggregation.
Cite this review
Pith. "Pith review of Wisdom of LLM Crowds: Aggregation and Contamination in Language Model Ensembles." pith.science (2026). https://pith.science/paper/QXY54JEB
@misc{pith2026260718269,
author = {Pith},
title = {Pith review of: Wisdom of LLM Crowds: Aggregation and Contamination in Language Model Ensembles},
year = {2026},
howpublished = {\url{https://pith.science/paper/QXY54JEB}},
note = {Machine review of arXiv:2607.18269}
}
read the original abstract
The wisdom of crowds -- the finding that aggregating judgments across individuals often outperforms the best individual -- has been extensively studied with human forecasters. Whether the same phenomenon emerges when the ``crowd'' consists of large language models (LLMs) is an open question with both theoretical and practical implications. We elicited probability estimates from 15 LLMs on 254 binary prediction market questions and evaluated classical and learned aggregation methods. Learned aggregators -- a multilayer perceptron and a logistic regression -- outperformed all individual models and classical methods. The logistic regression was found to match the neural network, suggesting that the benefit of learned aggregation derives from learning a linear combination of diverse model outputs rather than from nonlinear interactions. Symbolic regression applied to the neural network's learned mapping recovered a pure model-disagreement signal as the lowest-complexity useful formula on the Pareto frontier, further supporting this interpretation. Training cutoff contamination proved a pervasive confound: the apparent capability gap between frontier cloud models and smaller local models collapsed from 35.8% to 8.9% on a clean subset of questions resolving after all models' training cutoffs, and individual model rankings showed only moderate stability. Even when the prediction market is evaluated at each model's training cutoff, LLMs remained substantially less accurate, indicating a genuine gap in collective information aggregation. These findings suggest that LLM crowds can exhibit wisdom-of-crowds effects, but that contamination-free evaluation is essential for reliable assessment.
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This paper was first reviewed by deepseek-v4-flash on August 2, 2026.
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