The 2024 AI-dialogue paper's cross-topic belief spillover was a measured 8.2% drop on 15 unrelated conspiracies, not a claim about reasoning in general

conspiracy-beliefLLM-persuasionAI-epistemicsgeneralizationbelief-in-conspiracy-theories-index

Costello, Pennycook & Rand's 2024 study (Thomas Costello first author) measured belief on the 15-item Belief in Conspiracy Theories Index (BCTI) before and after a three-round AI dialogue that targeted only one, self-selected "focal" conspiracy per participant. The other 14, untouched items also moved [promotion wording; corrected 2026-10-16 against the capture-time archive (sha b5ff2aa1…) — there is no fixed "other 14." Each participant's focal conspiracy was elicited as free text and was "not necessarily one of the 15 rated earlier" (Study 1, archive l. 137–140), so how many BCTI items were untouched varies by participant. The paper computed three versions of the BCTI score (Methods, l. 643–656), and the spillover estimate is the non-focal one — "average belief across all non-focal conspiracies from the BCTI" (SM §2, l. 1057–58) — with items matching a participant's focal conspiracy dropped by a GPT-4 overlap-matching pass; Figure 4A's own caption reads "excluding the focal conspiracy, if it was one of those 15." The accurate description is "15 BCTI items, overlap-adjusted," not "the other 14." The 8.2% figure itself is unchanged]: "there was a 3.05-point decrease in general conspiracy beliefs in the active condition (95% CI [-3.90, -2.20], p < .001, 8.2% decrease...), compared to a 1.64-point increase in the control." The spillover was still detectable at the two-month follow-up.

This is the figure behind the qualitative description in claim-tailored-ai-dialogue-durably-reduced-conspiracy-belief ("generalized across a wide range of conspiracy theories") — an 8.2% average decrease on a fixed scale of unrelated items, not yet a characterization of what moved. A measured shift in a belief-score composite is compatible with several different underlying mechanisms (a change in how evidence is weighed; a mood or trust effect that happens to track a conspiracist-belief scale; a regression artifact) and does not by itself distinguish between them. It is the generalization half of the reversal of claim-conspiracy-belief-was-the-paradigm-case-of-evidence-immunity, stated at the precision the primary source actually supports.