Chapter 4 – Experimental learning 121 control trial, during first evocation. The reduction of induced nocebo hyperalgesia after attenuation was measured as the change in reported pain for the first nocebo trials between the first and second evocation. The first trials of each testing phase were selected since previous studies indicate the effect to be clearest in those trials 15,31. Difference scores between nocebo and control trials as mentioned above were only used for manipulation checks and descriptive purposes (Tables 1 and 2). To conduct mixed model analysis of variance (ANOVA), the assumptions of normality, independence and homogeneity of the variances were checked. Unless otherwise stated, the threshold for significance was set at P < 0.05. As an effect size measure, partial eta-squared (ηp 2) was calculated for analyses of primary and secondary outcomes, with ηp 2 of 0.01 considered small, 0.06 considered medium, and 0.14 large 32,33. Nocebo hyperalgesia induction First, to examine whether a significant nocebo response was present after nocebo induction, a 3x2 mixed model ANOVA was used, treating induction group as the between-subjects factor with 3 levels (partial reinforcement, continuous reinforcement, or sham) and magnitude of the nocebo response as a within-subjects factor with 2 levels (first nocebo trial, first control trial). A conservative Bonferroni correction was applied and the threshold for significance was set at P < 0.01. Where a significant interaction is detected, planned contrasts are analysed (2x2 mixed ANOVAs) between each of the pairs of experimental groups. Nocebo hyperalgesia attenuation In order to test the hypothesis that counterconditioning would be more effective than extinction in attenuating nocebo hyperalgesia, a 2x2 mixed
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