A systematic meta-analysis of the Stroop task in depression

Despite the extensive use of the Emotional Stroop task in depression, only qualitative reviews have been produced to date, and these reviews conclude that Stroop performance in depression is equivocal. The present meta-analysis addressed the need to summarize the data quantitatively. A thorough search of the literature was conducted and 47 published studies and unpublished doctoral dissertations were included in the analyses. The meta-analysis revealed large and robust depression-related Stroop effects (e.g., for clinically depressed versus control participants on negative stimuli, g=.98, and on positive stimuli, g=.87). Although the effects did not reflect a strong emotion-congruent bias, they did distinguish among levels of depressive experience, in that greater levels of depression severity were associated with larger between-groups effect sizes. Moreover, these effects have been obtained without priming procedures, or the presentation of self-relevant or disorder-congruent stimuli. These findings challenge schema-based theories of the Emotional Stroop effect and predictions based on previous qualitative reviews of the literature. The findings also suggest that further comparative behavioural research on the depression-related Stroop effect, at least among clinically depressed populations, is not necessary. Future research should address questions about underlying mechanisms and focus on a more direct measure of depression-related attentional bias.