REVIEW 3 major objections 6 minor 27 references
Is External Information Useful for Stance Detection with LLMs?
T0 review · 3 major / 6 minor · reviewed 2026-08-06 · deepseek-v4-flash
Pith's one-line read External information from Wikipedia or the web usually hurts LLM stance detection, cutting macro F1 by up to 27.9 percent.
desk verdict A wide, honest empirical study whose headline 'external info hurts' is entangled with a prompt-structure difference; fixable and worth sending to review. read the letter →
The pith
A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.
The reading
What carries the argument
The analytic instruments are the net adoption rate (NAR) and the harmful adoption rate (HAR), defined in Equation 1. NAR measures whether a model is more likely to produce a prediction matching the stance or sentiment it perceives in the external information when that information is present than when it is absent, and HAR measures whether such adoptions turn correct predictions into incorrect ones more often than the reverse. These rates convert the intuition that the model is swayed by the supplied text into a measurable quantity, giving a causal account of the performance drops observed in the main comparison.
What would settle it
A random-text control condition would settle the claim: present the same prompt with length-matched but stance-free filler text instead of Wikipedia or web-search excerpts, keeping the instruction sentence present in every condition. If macro F1 falls as much with filler as with real external information, then the degradation is a prompt-structure artifact, not evidence that external information biases LLM predictions.
Extended reading notes
Core claim
The central discovery is that external information from Wikipedia or web search degrades stance detection performance of LLMs in most cases rather than helping it. The paper shows this through a systematic comparison of eight LLMs on three datasets with 12 targets, where macro F1 drops by up to 27.9% relative to the no-information baseline. The degradation is explained by the models' tendency to adopt the stance and sentiment they perceive in the supplied information: net adoption rates are positive for nearly all model–dataset combinations, and the adoptions are more often harmful than helpful. The paper further shows that chain-of-thought prompting does not eliminate the degradation and that fine-tuning only narrows it, in contrast to a BERT-based baseline that benefits from the same external information.
Load-bearing premise
The load-bearing assumption is that the measured degradation comes from the content of the external information and not from the extra instruction sentence that is added only when external information is present; if the added sentence alone causes the drop, the central claim is not established.
Editorial extensions
If this is right
- In zero-shot use, Wikipedia and web-search excerpts should not be assumed to help LLM stance classifiers; in most model–dataset pairs they lower macro F1, so systems should be evaluated with and without them.
- The bias mechanism predicts that source reliability matters: a neutral or counter-stanced excerpt will push predictions in its direction even when the text itself says otherwise.
- Chain-of-thought prompting does not cure the bias, so instruction-based warnings not to adopt the information's stance are not an adequate safeguard.
- Fine-tuning with external information shrinks but does not eliminate the degradation, so mitigation requires more than continued training on the same prompt distribution.
- The contrast with the BERT-based baseline indicates that the degradation is not a property of the task or datasets but of how LLMs attend to supplied context.
Reading between the lines
- The same stance-adoption mechanism likely applies beyond three-way stance classification: any retrieved passage that carries a stance may shift an LLM's answer toward that stance.
- A concrete extension would be to score each retrieved passage's stance and re-weight or filter passages before prompting; the paper does not test such a mitigation.
- Taken further, a stance-tilted web source is not just a performance nuisance but a potential poisoning channel for deployed stance classifiers that consume external text.
Editorial analysis
A structured set of objections, weighed in public.
Referee Report
Summary. The paper asks whether adding external information (Wikipedia excerpts or web search results) to LLM prompts improves stance detection. Across eight LLMs, three datasets, and twelve targets, the authors report that external information degrades performance in most configurations, with macro-F1 drops up to 27.9%, in contrast to a fine-tuned BERT baseline (WS-BERT) that generally improves. They propose net adoption rate (NAR) and harmful adoption rate (HAR) metrics to show that models align predictions with the stance or sentiment of the provided information, and they test chain-of-thought prompting and LoRA fine-tuning as mitigations. The paper concludes that external information often harms LLM stance detection and should be used with caution.
Significance. If the central claim is secure, this is a useful cautionary result for the growing practice of augmenting LLM prompts with retrieved text: it would show that knowledge injection, which helps fine-tuned BERT-style models, can backfire for prompted LLMs. The study's strengths are its breadth (eight models, three datasets, multiple information sources, CoT variations, and fine-tuning), the release of code, and the introduction of NAR/HAR as interpretable diagnostics. However, the headline conclusion is not yet fully supported because the no-information baseline differs from the information condition in prompt structure, and because single-run results lack uncertainty quantification. With additional control experiments and statistical rigor, this could be a strong contribution to LLM robustness and stance detection research.
major comments (3)
- [Appendix B / Section 4.1] The central comparison is confounded. In the non-CoT prompt, the information condition adds the sentence "The following information can be helpful: {wiki}." and the no-information condition omits this sentence entirely. In the zero-shot and few-shot CoT prompts, the information condition adds "Integrate the following external information and do NOT automatically adopt the stance of it: {wiki}.", and again this whole sentence is absent in the no-information baseline. Every performance difference in Table 1 therefore conflates the semantic content of the external information with a prompt-structure change: an extra instruction sentence, an explicit directive about stance adoption, and greater prompt length. The abstract and Section 4.1 attribute the degradation to "such information" / "external information," which is a causal claim about content. This cannot be sustained without a control condition that matches the prompt structure while varying only the content—for example, inserting a random or irrelevant text of similar length, or explicitly stating "No additional information is provided." The length-correlation analysis in Figure 2 does not resolve this, since all points in that figure already have the extra sentence present; length is not presence. This issue must be fixed or the claims rephrased as "adding an instruction sentence together with external information degrades performance."
- [Section 3.1 / Table 1] The paper reports single runs with no variance estimates or significance tests. Section 3.1 justifies single runs by temperature zero producing "negligible variation in performance," but this does not eliminate sampling variability in the test set or sensitivity to prompt and decoding details, and API models can be nondeterministic. Many of the reported changes are small (e.g., -0.2% accuracy for Llama-3.1-8B on COVID-19-Stance with Wikipedia, Table 1), so without standard errors or bootstrap confidence intervals the sign of the change is not reliable. The aggregate claim "external information decreases performance in most cases" is literally a count of negative cells in Table 1, so the absence of uncertainty quantification is load-bearing. Please provide repeated runs or resampling-based confidence intervals, at least for the main no-info-vs-Wikipedia comparison, and report how many individual differences are statistically distinguishable from zero.
- [Section 4.2, Eq. (1), and Figure 2] The NAR/HAR analysis and the length correlation inherit the confound described in the first major comment. The definition of NAR compares M(x|t,T) with M(x|∅,T), where the latter omits the entire instruction sentence; the observed positive net adoption could therefore reflect the model reacting to the added sentence rather than to the stance or sentiment of the information content. Figure 2 correlates length with prediction rates and relative performance only within information-present conditions, so it does not test whether the presence of the extra sentence is the cause. Additionally, s = M(t|∅,T) is the model's stance or sentiment of the information obtained through a separate, simpler prompt (Appendix B), which is a different task from stance detection of the tweet; the paper does not validate that this isolated perception matches how the model internally represents the information when it is embedded in the detection prompt. Please either add the missing control or explicitly limit the NAR/HAR claims to "under this prompt structure," and consider validating the perceived-stance prompt against a fixed external sentiment model.
minor comments (6)
- [Appendix B] The omitted sentences are marked in red, which is not visible in a grayscale printout; please use a clearer notation such as brackets or a footnote indicator.
- [Section 3.1] The claim of "negligible variation in performance" should be quantified; if possible, report the observed variance from a few pilot runs or a range rather than an informal assertion.
- [Figure 2] The p-values are reported without multiple-comparison correction; with four correlations, the one significant result (p=0.004) should be interpreted cautiously, and the text should note this.
- [Section 4.4 / Table A2] The fine-tuning analysis reports counts of instances with negative relative performance but does not distinguish large negative changes from small ones near zero; adding a magnitude summary (as in Table A3) in the main text would help the reader judge the practical relevance.
- [Section 3.2] The external information for SemEval 2016 Task 6 was collected by the authors via the Wikipedia API; a brief description of the extraction process and any manual quality checks would improve reproducibility.
- [Section 6] The Limitations section does not mention the prompt-structure difference between the no-info and info conditions; even if the control experiments are added, this limitation should be discussed explicitly.
Circularity Check
No significant circularity: the central degradation finding is an empirical comparison against a no-information baseline, not a result forced by the paper's definitions or by self-citation.
full rationale
This paper is an empirical evaluation and contains no mathematical derivation chain whose conclusion is equivalent to its inputs by construction. The central claim that external information degrades LLM stance detection is supported by direct measurements of macro F1 and accuracy with and without external information (Table 1), where the no-information baseline is an independent condition rather than a fitted parameter or a model output reused as the prediction. The NAR/HAR metrics are self-referential in that s is defined as the model's own perceived stance or sentiment of the information (Equation 1: 's = M(t|∅,T) is the stance or sentiment ... M detects for t'), but this does not force the degradation conclusion; NAR merely quantifies how often predictions move toward the model's perception, and HAR separately measures whether such moves are harmful or helpful. The explanation that models adopt information stance is thus an interpretive statistic, not a tautology that determines the headline result. There are no load-bearing self-citations: the papers cited for external information and BERT baselines (He et al., 2022; Li et al., 2021; Mohammad et al., 2016) are prior work by other authors, and no uniqueness theorem or prior result by the present authors is invoked to rule out alternatives. The reviewer's concern that the no-information prompt omits the entire instruction sentence introducing the external information is a potential confound about causal attribution, but it is not circularity: the comparison is still an empirical measurement, and the confound does not make the reported degradation equivalent to the paper's own assumptions by definition. For these reasons, the appropriate finding is no significant circularity.
Assumptions & free parameters
assumptions (3)
- domain assumption LLM outputs are deterministic at temperature 0, so single runs are representative.
- domain assumption The no-information baseline is a valid control, despite the prompt sentence being omitted.
- domain assumption Wikipedia excerpts (from He et al., 2022) and web-search summaries are typical external information for stance detection.
Cite this review
Pith. "Pith review of Is External Information Useful for Stance Detection with LLMs?." pith.science (2026). https://pith.science/paper/V5DBESZD
@misc{pith2026250701543,
author = {Pith},
title = {Pith review of: Is External Information Useful for Stance Detection with LLMs?},
year = {2026},
howpublished = {\url{https://pith.science/paper/V5DBESZD}},
note = {Machine review of arXiv:2507.01543}
}
read the original abstract
In the stance detection task, a text is classified as either favorable, opposing, or neutral towards a target. Prior work suggests that the use of external information, e.g., excerpts from Wikipedia, improves stance detection performance. However, whether or not such information can benefit large language models (LLMs) remains an unanswered question, despite their wide adoption in many reasoning tasks. In this study, we conduct a systematic evaluation on how Wikipedia and web search external information can affect stance detection across eight LLMs and in three datasets with 12 targets. Surprisingly, we find that such information degrades performance in most cases, with macro F1 scores dropping by up to 27.9\%. We explain this through experiments showing LLMs' tendency to align their predictions with the stance and sentiment of the provided information rather than the ground truth stance of the given text. We also find that performance degradation persists with chain-of-thought prompting, while fine-tuning mitigates but does not fully eliminate it. Our findings, in contrast to previous literature on BERT-based systems which suggests that external information enhances performance, highlight the risks of information biases in LLM-based stance classifiers. Code is available at https://github.com/ngqm/acl2025-stance-detection.
Figures
Reference graph
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Reviewed August 6, 2026 · model on record in the stance chip above.
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