2.3. Assessment

The German version of the Obsessive–Compulsive Inventory-Revised (OCI-R; ^{Foa et al., 2002; Gönner, Leonhart, & Ecker, 2008}) was used to assess the severity of participants’ OCD. Studies have shown the inventory has good to excellent psychometric properties (^{Foa et al., 2002; Huppert et al., 2007}), and its administration via the Internet has been shown to be equivalent to paper-and-pencil administration (^{Coles, Cook, & Blake, 2007}). In addition to the total score, six subscales may be calculated: washing (items 5, 11, and 17), obsessing (items 6, 12, and 18), checking (items 2, 8, and 14), neutralizing (items 4, 10, and 16), hoarding (items 1, 7, and 13), and ordering (items 3, 9, and 15). Clinical benchmarks and norm values have recently been published for the English version of the OCI-R, with 0–15 points indicating mild, 16–27 points moderate, and 28–72 points severe OCD (^{Abramovitch, Abramowitz, Riemann, & McKay, 2020}).

To assess severity of depression, we used the German version of the Patient Health Questionnaire (PHQ-9, ^{Löwe, Kroenke, Herzog, & Gräfe, 2004}). The PHQ-9 represents the depression module of the PHQ-D and uses 9 items rated on a 4-point Likert-scale (response options rated over the last two weeks: 0 = not at all, 1 = several days, 2 = more than half the days, 3 = nearly every day). Accordingly, scores range from 0 to 27. For the English version, ^{Kroenke, Spitzer, and Williams (2001)} have suggested that total scores of 5, 10, 15, and 20 points refer to mild, moderate, moderately severe, and severe depression, respectively. The questionnaire has good validity and reliability (^{Löwe et al., 2004; Martin, Rief, Klaiberg, & Braehler, 2006})