Brendan Nyhan reports independently reproducing Costello, Pennycook & Rand's 2024 AI-debunking finding in two experiments at Dartmouth

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Political scientist Brendan Nyhan — who has no co-authorship on either Costello paper — told Retraction Watch that "he and his students have reproduced the paper's results in two independent experiments at Dartmouth College in New Hampshire." The report appears in the same Retraction Watch piece covering the Science Expression of Concern on the 2024 paper.

Nyhan's replication is the nearest thing to genuine independent corroboration — different author, different institution — found anywhere in the Costello/Pennycook/Rand conspiracy-persuasion research program (see question-corroborate-costello-2026-arxiv-2601-05050-single-source-cap). But it reproduces the 2024 debunking-only finding (claim-tailored-ai-dialogue-durably-reduced-conspiracy-belief), not the 2026 bunking/debunking symmetry result in claim-llm-conspiracy-persuasion-is-dual-use and claim-2026-symmetry-result-answers-a-question-2024-paper-posed — a symmetry the 2026 paper itself scopes to a model that is not instructed to be truthful, since under its truth-constrained condition bunking was "much less effective than debunking (z = 4.1, p < .001)" and "Truth had an advantage." It therefore does not discharge the single-source concentration cap on arXiv 2601.05050, which requires independent corroboration of that preprint's own findings specifically. No equivalent independent replication of the 2026 paper's symmetry or dual-use findings has been located.