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Category: Analysis

Description: To evaluate the required sample size for the current project, we performed a power analysis, for which we randomly sampled n = 8 participants (ΔTime from lockdown relief: M = 23.13 days, SD = 11.34, range = [9, 46] ; ΔTime between scans: M = 247 days, SD = 144 days, range = [137, 543]), and n = 8 control participants who also performed two T1w scans, but both were prior to the lockdown period (ΔTime between scans: M = 155 days, SD = 130 days, range = [80, 474]). We performed a Voxel-Based Morphometry (VBM) analysis for the T1w MPRAGE scans of each participant, using the ‘Computational Analysis Toolbox 12’ (CAT12; www.neuro.uni-jena.de/cat/). Voxel-based data were aggregated across structural brain atlas (Hammers et al., 2003) for each participant. We focused on the interaction effect of a linear mixed model, contrasting the differences of the two time-points between the Control and test group (Time X Group interaction; i.e. is the difference in VBM stronger for the test group than the control group?). To model this interaction effect, we calculated for each region the within-subject difference in grey matter regional volume between the two time-points and contrasted the mean difference between the groups in a two-sample t-test. A power analysis was performed for each anatomical ROI using the effect sizes observed in our data with 80% power to detect a significant interaction effect with α = .05, using R ‘pwr’ package (Champely et al., 2018). To decide on the appropriate sample size, we examined the anatomical ROIs which showed both a significant change effect for the experiment group (n = 8), and a significant interaction effect between the two groups, with a loose statistical threshold of p = 0.25. We selected to use n = 37 per group as our target sample size, which would provide sufficient power to detect our effect of interest both in the left and right amygdala. In this OSF section we include the preprocessed data and the analysis codes used to decide the minimal sample size for this project (n = 37 per each group, total N = 74).