... During the past decades, psychotherapy research has repeatedly supported the equivalent efficacy of diverse models of psychotherapy (Barber, Muran, McCarthy, & Keefe, 2013;Elliott, Greenberg, Watson, Timulak, & Freire, 2013;Lambert, 2013;Smith & Glass, 1977;Wampold et al., 1997;Wampold & Imel, 2015), the central importance of the therapeutic alliance (Flückiger, Del Re, Wampold, Symonds, & Horvath, 2012;Horvath, Del Re, Flückiger, & Symonds, 2011), and the existence of principles of change that span across specific treatment models (e.g., Goldfried, 2009). More recently, there has also been an increased focus on the differential effects of therapists, which are seemingly not attributable to the therapists' adherence to particular theoretical orientations (e.g., Blatt, Sanislow, Zuroff, & Pilkonis, 1996;Huppert et al., 2001;Kim, Wampold, & Bolt, 2006;Webb, DeRubeis, & Barber, 2010). ...