“…Frequently researched therapist variables are the therapists’ theoretical background/orientation (Anderson, Ogles, Patterson, Lambert, & Vermeersch, 2009 ; Berglar et al, 2016 ; Okiishi et al, 2006 ), professional interpersonal skills or self-rated professional characteristics (Heinonen & Nissen-Lie, 2019 ), therapists’ alliance-building behaviours (Jungbluth & Shirk, 2009 ; Ovenstad, Ormhaug, Shirk, & Jensen, 2020 ), professional experience (e.g. years of experience doing therapy; Huppert et al, 2001 ; Turner, Nicholson, & Sanders, 2011 ), age (Anderson et al, 2009 ; Schauenburg, Dinger, & Strack, 2005 ) and gender (Shiner, Westgate, Harik, Watts, & Schnurr, 2017 ; Zorzella, Muller, & Cribbie, 2015 ). However, these studies have investigated very heterogeneous samples and the results regarding the impact of the therapist variables on outcome are highly contradictory.…”