162 In an exploratory manner, we further analyzed whether the magnitude of nocebo hyperalgesia at the end of extinction differed between groups, for High-pain vs. Control and High-threat vs. Control. To compare each of the fear groups to the control group, two 2x2 mixed model ANOVAs were conducted, with group as the between-subjects factor and trial type as within-subjects factor (last nocebo, last control extinction trials). Mediation analyses For the High-pain group, we expected that any effects of higher pain stimulation on the magnitude or reduction of nocebo hyperalgesia would be mediated by pain-related fear. Only when ANOVA results were significant, mediation analyses were conducted, to assess if fear mediated the relationship between pain level and the magnitude of nocebo hyperalgesia. Calculation of indirect effects and bootstrapping tests of mediation were performed, using the PROCESS macro for SPSS 43,44, with 5000 bootstrap samples. Separate mediation analyses were conducted for the self-report and startle response fear measures (mediator variables). Group (High-pain, Control) was the dichotomous predictor variable. Mediation analyses were not planned for the Highfear group, as an increase in fear is inherent to the threat manipulation. Manipulation checks for fear levels We examined whether increased pain levels and the threat manipulation led to higher fear levels. Mixed-model ANOVAs were performed, separately for reported fear and for startle responses, one for High-pain group vs. Control and one for High-threat group vs. Control. Group was the between-subjects factor and trial type was the within-subjects factor (nocebo, control).
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