Cognitive bias modification (CBM) interventions are strongly advocated in research and clinical practice.

We aimed to examine the efficiency of CBM for clinically relevant outcomes, along with study quality, publication bias and potential moderators.

We conducted two meta-analyses of randomized controlled trials of CBM interventions for clinically relevant outcomes, one for patients with mental health problems and one for all populations. We included randomized controlled trials of CBM interventions, which reported clinically relevant outcomes assessed with standardized instruments. We examined the quality of the trials, as well as possible publication bias and possible moderators.

We identified 49 trials and grouped outcomes into anxiety and depression. ESs were small considering all the samples, and mostly non-significant for patient samples. ESs became non-significant when outliers were excluded and after adjustment for publication bias. The quality of the RCTs was sub-optimal. Publication year was consistently negatively associated with ESs. More sessions were associated with smaller ES, as were the absence of participant compensation and, respectively, the non-exclusively laboratory based delivery of the intervention. The quality of the RCTs was not optimal and quality was negatively associated to outcomes for depression and general anxiety.

Our results indicate that CBM may have small effects on mental health problems, but it is also very well possible that there are no significant effects. Research in this field is hampered by small and low-quality research, and by risk of publication bias, and much of the positive outcomes is driven by extreme outliers.