128 Normality checks The ANOVA assumptions of normality, independence, and homogeneity of the variances were checked. A non-significant ShapiroWilk test and histograms of standardized residuals indicated a normal distribution of the data. Within- and between-groups independence was established by randomization into groups. Homogeneity of variances was tested via a Levene's test, which indicated non-significant results, thereby confirming homogeneity of variance in the data. Nocebo hyperalgesia induction The mean magnitudes of reported nocebo hyperalgesia after induction are listed in Table 2. A 3x2 mixed model ANOVA was conducted to establish whether there was a significant difference in the magnitude of induced nocebo hyperalgesia between partial reinforcement, continuous reinforcement, and sham. The analysis revealed a significant group by trial interaction between the 3 induction groups and the magnitude of nocebo responses (F (2,119) = 20.75, P < 0.001, ηp 2 = 0.26). Figure 2 illustrates the differences in pain ratings for the first nocebo trial and the first control trial of the first evocation, across all three groups. Three 2x2 mixed model ANOVA planned analyses revealed a significant interaction between the partial reinforcement and sham group and the magnitude of nocebo responses (F (1,72) = 20.58, P < 0.001, ηp 2 = 0.22), between the continuous reinforcement and sham group and the magnitude of nocebo responses (F(1,71) = 45.22, P < 0.001, ηp 2 = 0.39), and between the partial reinforcement and continuous reinforcement groups and the magnitude of nocebo responses (F (1,95) = 7.28, P = 0.008, ηp 2 = 0.07). These results indicated that conditioning with partial reinforcement and with continuous reinforcement were both effective in inducing significant nocebo responses, with continuous reinforcement producing a significantly larger nocebo response as compared to partial reinforcement.
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