The Barnum Effect Over Time: A Longitudinal Study Among Chinese Female Participants

Abstract

The Barnum effect—the tendency to accept vague, generalized personality descriptions as uniquely accurate—is one of the most robust findings in psychology. However, nearly all existing studies have measured this effect immediately after feedback is given, and no study has separated the priming effect of completing a personality test from the temporal persistence of the Barnum Effect, leaving two critical question unanswered: (1) Does the Barnum effect persist over time? (2) Does completing a self-reflecting personality questionnaire enhance the Barnum Effect?  This study investigated these questions using a longitudinal independent measures design with three groups. Participants in the control group (n = 61) read the Barnum descriptions directly and rated their accuracy. Participants in the immediate-rating group (n = 79) completed a 15-item personality questionnaire (BFI-S) prior to reading and rating the descriptions. Participants in the delayed-rating group (n = 50) completed the same questionnaire and read the same descriptions, but rated their accuracy seven days later. All participants in the two experimental groups were female. Results showed that the immediate-rating group rated the descriptions as more accurate than the control group (M = 4.01 vs. 3.79, p = 0.086, d = 0.30), suggesting that self-reflective priming enhances the effect. Critically, the delayed-rating group (M = 4.16) rated the descriptions as numerically higher than the immediate-rating group (M = 4.01, p = 0.25, d = 0.21), indicating that the Barnum Effect not only persisted over the one-week interval but showed a small increase. A one-way ANOVA test confirmed no significant overall difference among the three groups, F(2, 187) = 2.01, p = 0.137, consistent with the interpretation that the effect remained stable over time. These findings provide evidence that the Barnum Effect is durable and can be enhanced by completing a personality test before rating, suggesting that generic personality feedback can shape self-perception beyond the immediate context in which it is received.