Subthreshold depression (sD) is defined as the presence of elevated symptoms of depression without fulfilling full criteria for Major Depressive Disorder (MDD) (Volz et al., 2022). Subthreshold depression is highly prevalent (Cuijpers et al., 2004), associated with poorer quality of life (Rucci et al., 2003), higher functional impairment (Backenstrass et al., 2006; Karsten et al., 2013) and a higher risk of developing MDD (Cuijpers and Smit, 2004; Lee et al., 2019), calling for intervention options (Volz et al., 2022). Meta-analytic evidence shows that psychological interventions can reduce the incidence of depression by 20% (Relative Risk = 0.81; 95% CI: 0.72–0.91) (Cuijpers et al., 2021) and reduce depressive symptom severity (Cuijpers et al., 2014). Similarly, low-threshold preventive internet interventions have shown potential to reduce the risk of depression onset in individuals with sD (Hazard Ratio = 0.72; 95% CI: 0.58–0.89) and reduce symptom severity (Reins et al., 2021). However, to further increase the effectiveness of preventive IMIs for depression, it is important to investigate factors that are associated with treatment outcome. Outcome expectancy - that is, paticipant’s belief of whether treatment will lead to an improvement in health status (Constantino et al., 2011; Thiruchselvam et al., 2019) – is discussed as a common factor that influences psychotherapy outcome (Cuijpers et al., 2019; Greenberg et al., 2006). This has been shown across different therapeutic approaches, including cognitive behavioral therapy (CBT) and different formats like individual (Constantino et al., 2011), group (Abouguendia et al., 2004; Safren et al., 1997), and couple therapy (Tambling, 2012). The effects of outcome expectations have been shown to be at least partly mediated by the therapeutic alliance (Abouguendia et al., 2004; Constantino et al., 2018; Vîslă et al., 2018) and influenced by patient’s age, degree of standardization in therapy and measurement instrument for outcome expectancy (Constantino et al., 2018). A recent meta-analysis summarized being female, of older age, therapy experienced, generally hopeful and psychologically minded as well as having less severe baseline symptoms were positively associated with initial outcome expectancies (Constantino et al., 2018). Visla and colleagues (2019) added having experienced previous depressive episodes and reporting lower well being as predictors of low initial outcome expectancies. Besides its positive influence on treatment outcome, low or pessimistic treatment expectancy could pose a warning mechanism for possible negative treatment effects (Locher et al., 2019; Petrie and Rief, 2019). In the field internet interventions, outcome expectancy has primarily been studied in terms of acceptability and uptake of diverse internet health services (Beatty and Binnion, 2016; Musiat et al., 2014; Philippi et al., 2021), but less in its persisting effects on the desired outcome. The few studies investigating the effect of participants’ expectancies on depression treatment outcomes remain inconclusive, with three studies supporting outcome expectancy as being predictive for treatment outcome (El Alaoui et al., 2016; de Graaf et al., 2009; Pearson et al., 2019) whereas three other studies did not find such an association (Cavanagh et al., 2009; Høifødt et al., 2015; Lüdtke et al., 2018) and one study reports an association fully mediated by therapeutic alliance (Zagorscak et al., 2020). For preventive intervention, evidence from studies investigating preventive IMIs for Generalized Anxiety Disorder and Obsessive Compulsive Disorders are also inconclusive, with outcome expectancy being correlated with reduction in anxiety symptoms (Kenardy et al., 2003) but not associated with post-treatment OCD symptoms (Boisseau et al., 2017). However, to our best knowledge, no study has investigated outcome expectancy for preventive interventions for depression. Therefore, the aim of this study is to explore the predictive role of outcome expectancy in an IMI for sD in terms of depressive symptom severity and depression onset. References Abouguendia, M., Joyce, A.S., Piper, W.E., Ogrodniczuk, J.S., 2004. Alliance as a Mediator of Expectancy Effects in Short-Term Group Psychotherapy. Gr. Dyn. 8, 3–12. https://doi.org/10.1037/1089-2699.8.1.3 Alaoui, S. El, Ljótsson, B., Hedman, E., Svanborg, C., Kaldo, V., Lindefors, N., 2016. 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