Truth by repetition reliably differs between people over time

Repetition increases the believability of information. Despite the assumedly widespread (harmful) implications of this truth-by-repetition effect (TBRE), little is known about if and how repetition influences people differently. Across two longitudinal experiments (N1 = 113, Belgium; N2 = 430, UK), each consisting of five sessions over 33 days, we collected 108,600 truth judgments. Analyses showed that people differ in their TBRE across time, suggesting a trait-like disposition, which covaried with their Preference for Fluency. Notably, many participants showed stable TBREs that were small or close to zero, whereas relatively few showed large TBREs. We found no evidence for negative TBREs whereby repetition meaningfully decreases believability. The results highlight the value of multiple assessments and challenge the idea of a universal TBRE; repetition increases the believability of information – but not for everyone, and more so for some than others.