The Architecture Was Doing the Work: Why NLI Debiasing Results Do Not Generalise

Prabhjot Singh


Abstract
NLI debiasing research evaluates interventions on single architectures and datasets, leaving a critical assumption untested: do improvements reflect method quality or model capacity? We run 44 controlled experiments: eleven debiasing strategies across two architecturally distinct models (ELECTRA-small, RoBERTa-base) and two corpora (SNLI, MNLI), under identical conditions with Wilson 95% confidence intervals throughout. On ELECTRA-small, which achieves 87.4% in-domain accuracy, debiasing fails completely: all ten debiasing interventions fall within the baseline confidence interval on HANS (CoV = 0.75%). On RoBERTa-base, methods show genuine sensitivity (CoV = 10.76%, approximately 14x higher), yet the median intervention trends toward degrading OOD accuracy on SNLI, short of conventional significance (Wilcoxon p = 0.065), and method rankings across corpora are anti-correlated for ELECTRA (Spearman ρ = -0.42) but stable for RoBERTa (ρ = 0.75). Contrastive augmentation swings 5.6 pp across corpora (+3.59 pp MNLI, -2.02 pp SNLI). The positive robustness-accuracy correlation on RoBERTa (r = 0.848) inverts the assumed tradeoff: methods that improve HANS also preserve in-domain accuracy, while aggressive debiasers collapse both. The ELECTRA failure is not a pipeline artefact; the same codebase produces real gains on RoBERTa. It is a capacity failure: debiasing presupposes representational capacity that small architectures lack, a precondition the literature neither states nor tests.
Anthology ID:
2026.insights-1.10
Volume:
Proceedings of the Seventh Workshop on Insights from Negative Results in NLP
Month:
October
Year:
2026
Address:
Budapest, Hungary
Editors:
João Sedoc, Raphael Shu, Aleksandr Drozd, Arjun Akula, Anna Rogers, Salvatore Giorgi, Adrian Benton
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insights | WS
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Publisher:
Association for Computational Linguistics
Note:
Pages:
84–89
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URL:
https://aclanthology.org/2026.insights-1.10/
DOI:
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Cite (ACL):
Prabhjot Singh. 2026. The Architecture Was Doing the Work: Why NLI Debiasing Results Do Not Generalise. In Proceedings of the Seventh Workshop on Insights from Negative Results in NLP, pages 84–89, Budapest, Hungary. Association for Computational Linguistics.
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The Architecture Was Doing the Work: Why NLI Debiasing Results Do Not Generalise (Singh, insights 2026)
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