Martijn van Teffelen

Interpretation bias modification for hostility 125 6 INTRODUCTION Hostility is a trait constellation consisting of a tendency to hold a hostile attributional style, experience angry affect, and behave aggressively, and is considered a trans-diagnostic clinical phenomenon (Cassiello-Robbins & Barlow, 2016). Clear prevalence estimates in clinical samples are currently missing, however one observational study in 3800 outpatients indicated that 43.60% reported moderate to severe anger and 21.20% reported moderate to severe aggressive behavior in the preceding week (Genovese et al., 2017). Next to a profound impact on negative interpersonal functioning (Henrichs et al., 2014), hostility is associated with increased psychopathological severity (Cassiello-Robbins & Barlow, 2016) and suicidality (Ammerman et al., 2015). Treatment options for hostility exist. However, effects appear less pronounced than those for other psychopathologies (e.g., panic disorder, and body dysmorphic disorder), as 34% of patients do not profit from treatment (Hofmann et al., 2012). Moreover, premature treatment discontinuation in patients with psychopathology is significant (Arntz et al., 2015; Cassiello- Robbins et al., 2015; Putt et al., 2001) and few high-quality treatment effects studies on hostility have been conducted (Del Vecchio & O’Leary, 2004). Furthermore, patients with increased levels of hostility are often described by therapists as ‘challenging’ (von der Lippe et al., 2008). One potential promising novel way of reducing hostility is offered by cognitive bias modification for interpretation bias (CBM-I). CBM-I is a computerized procedure that targets an important aspect of hostility, i.e. hostile interpretation bias (HIB), referring to a tendency to interpret emotionally ambiguous scenarios in a hostile way. This is achieved by presenting patients with many (unfamiliar) emotionally ambiguous scenarios on a computer followed by a reinforcement of benign instead of hostile interpretations (Mathews & Mackintosh, 2000). In the present work, we aim to investigate the effects of CBM-I on HIB in one randomized sham-controlled feasibility trial and one randomized sham-controlled clinical trial. Initially, meta-analytic evidence supported the efficacy of CBM-I on anxiety- and depression- related biases with a pooled effect size of g = .81 (Hallion & Ruscio, 2011). More recently, a meta- analysis on the efficacy of CBM-I on anxiety and depressive symptomatology revealed only small standardized mean differences (SMD) of SMD = -.30 for anxiety symptoms and SMD = -.26 for depressive symptoms (Fodor et al., 2020). However, inconsistency of findings (specifically for depression trials), heterogeneity, and risk of bias potentially impede reliable interpretation of these findings. Thus, at present it is unclear whether CBM-I is efficacious at all, and how large the effect is. Moreover, these meta-analytic studies on the effects of CBM-I in anxiety and depression did not include HIB as an outcome. Preliminary evidence supporting the efficacy of CBM-I on HIB is provided by five studies. A first study showed that HIB can be experimentally