50 Chapter 3 In all models our effect of interest was the testosterone x time interaction. In all analyses the independent continuous predictors were centered and sum to zero contrasts were used. In line with recommendations for mixed models (Pek & Flora, 2018), we report unstandardized effect sizes (i.e. the estimates). In-session fear analyses For the analyses regarding fear levels, all peak SUD scores during the speech exposure session were modeled as the dependent variable. Testosterone (baseline or reactive) and Time (speech 1, 2 and 3, in the exposure session) were included as predictors (fixed factors). Participant was included as random slope and intercept and gender, age and initial symptom severity (i.e. baseline LSAS scores) were included as covariates. In addition to the in-session fear analyses, we conducted analyses to see whether testosterone levels were related to fear reduction across sessions (i.e. from speech 1 to speech 4 one week later), therefore the same analysis was repeated for fear levels with Time (Speech 1, Speech 4). Symptom severity analyses LSAS scores were the dependent variable; Testosterone (reactive or baseline) and Time (pre/post assessment) were included as predictors, Participant as random intercept, and Gender and Age as covariates. Results Sample characteristics As expected, testosterone levels were higher for males compared to females (all p-values <0.001) and showed a negative (though non-significant) relation with age (correlations for males ranged from -.17 to -.30 and for females from -.11 to -.22, all p-values >.050). Log-transformations were performed to handle the non-normality of testosterone data. To be able to combine data of females and males, baseline testosterone was standardized per gender (see also Tyborowska, Toni, Roelofs, Volman, & Smeekens (2016)). Means and standard deviations of the non-transformed data are presented in Table 3.1. Because we detected one multivariate outlier in the data for baseline as well as reactive testosterone, we repeated the analyses after winsorizing testosterone. For this procedure, extreme values were set to the second and 98th percentile of baseline and reactive testosterone to reduce the effect of spurious outliers. The results remained the same after this procedure (see chapter 3 – appendix 2 for details).
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