The truth about the truth: a meta-analytic review of the truth effect.

Repetition has been shown to increase subjective truth ratings of trivia statements. This truth effect can be measured in two ways: (a) as the increase in subjective truth from the first to the second encounter (within-items criterion) and (b) as the difference in truth ratings between repeated and other new statements (between-items criterion). Qualitative differences are assumed between the processes underlying both criteria. A meta-analysis of the truth effect was conducted that compared the two criteria. In all, 51 studies of the repetition-induced truth effect were included in the analysis. Results indicate that the between-items effect is larger than the within-items effect. Moderator analyses reveal that several moderators affect both effects differentially. This lends support to the notion that different psychological comparison processes may underlie the two effects. The results are discussed within the processing fluency account of the truth effect.