49 Endogenous testosterone levels are predictive of symptom reduction with exposure therapy in social anxiety disorder The samples were stored at -20 °C until radio immune assays were performed by Dr. Clemens Kirschbaum’s laboratory in Dresden, Germany, for descriptions of specific methodology used by this laboratory, see: (Miller, Plessow, Kirschbaum, & Stalder, 2013; Reardon, Herzhoff, & Tackett, 2016). Procedures After informed consent, participants were screened for eligibility via questionnaires. All participants were telephoned afterwards for further screening (using the Mini-International Neuropsychiatric Interview (MINI; (Sheehan et al., 1998)) to assess for study inclusion and exclusion criteria), and were invited to participate in the study. After enrollment, participants were randomly assigned to a posture condition (power, submissive or no posture/rest). Saliva was collected at the mentioned time points in the Saliva Measures section and the posture manipulation protocol was performed. Afterwards, participants participated in the standardized exposure session. One week after the standardized exposure session, participants completed the same 5-min speech as during the exposure session to assess for post-treatment levels of speech fear. Fear levels were assessed at the beginning (initial) and immediately after all the speeches (end and peak SUDs). Participants completed the LSAS prior to the speech exposure session and at post-treatment. See Davis et al. (2017) for a detailed description of the study procedures. Statistical analyses To test the hypothesis that testosterone reactivity in preparation for a challenging encounter facilitates fear reduction, we focused on pre-exposure testosterone levels: Testosterone reactivity was calculated for each individual, based on the absolute difference in testosterone levels from the start (Sample 1) to the pre-exposure sample (Sample 3). The resulting subtraction-value was divided by the start (Sample 1) level to control for initial differences (for a similar method see Jiménez et al., 2012; Zilioli et al., 2014). We used sample 3 versus 1 to capture the full anticipatory period from arriving in the lab until the start of the first speech. In addition, we computed individual baseline testosterone levels by averaging both pre-power posing samples (1 and 2). For all statistical analyses, both reactive and baseline testosterone values were standardized per gender. To test effects of testosterone responses on exposure outcome (in-session fear and symptom levels), we conducted separate mixed model analyses, using the Lme4 package in R (Bates, Maechler, Bolker, & Walker, 2013). P-values were calculated using the Likelihood Ratio Tests using the mixed function in the Afex package (Singmann, 2013). We ran four separate models: namely for baseline and for reactive testosterone levels separately and with fear levels and symptom severity as dependent variables separately. 3
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