Martijn van Teffelen

Chapter 4 82 Procedure The Ethical Review Committee Psychology and Neuroscience at Maastricht University provided ethical approval to carry out the study (ERCPN-185_07_11_2017_A1). The study was preregistered at https://osf.io/j9ngp. 1 Data was gathered from November 2018 to February 2020. Respondents were screened for eligibility by e-mail using the PID-5. Respondents who were eligible for the study were randomly assigned to the conditions (I-CR, CR, AC) using permutated block randomization, stratified by gender. Randomization was carried out by an independent technician from another department at Maastricht University. The participants were blind to the condition. When participants arrived at the lab the study’s procedure was explained, and written informed consent was obtained. The study consisted of two sessions one week apart from each other. The first session took approximately 90 minutes, the second session approximately 30 minutes. The first session started with a baseline assessment (M0). Then participants received psycho-education, after which they completed M1. After the imagery transformation/thought diary completion, right before engaging in the allocated intervention, participants received M2. The intervention continued following protocol and after the intervention, M3 took place. The second session started with a baseline measurement 4 (M4). Then participants briefly recalled their autobiographical memory. After this, all participants engaged in the imagery-interview (i.e., the emotional stressor) which was preceded with M5 and followed by M6. For a graphical overview of the procedure, see Appendix A. At the end of the second session, we conducted an exit-interview in which we asked participants to rate on a VAS from 0 (not at all) to 100 (very much) how exhausting the intervention was, how emotional it was for them, and (if participants were in the I-CR condition) how vividly they could see the mental images and what percentage of the time they saw the mental image when they had their eyes closed. Last, participants were debriefed and received a financial compensation of €15 or course credits. Statistical analyses SPSS version 24 was used for all analyses. First, means and standard deviations were computed to examine the baseline characteristics of all study variables. Second, independent samples t -tests were run to test for baseline differences. Third, multilevel mixed effects regression were run to test the hypotheses that I-CR is more efficacious in reducing hostile beliefs (H1), aggressive tendencies (H2), anger (H3), and hostility traits (H4) compared to traditional CR and the AC conditions. Whenwe analyzed whether both interventions, I-CR and CR, were more efficacious than the AC condition, the AC condition was selected as reference category. To test the difference between I-CR and CR, CRwas selected as reference category. Hostile beliefs, aggressive tendencies, anger, and hostility 1 In the pre-registration hostile beliefs are referred to as ‘threat appraisals’. Also, the present paper did not include the pre-registered analysis of physiological measures; these were intended to be published elsewhere.