Quantifying the effects of the differential outcomes procedure in humans: A systematic review and a meta-analysis

We present a systematic review and a meta-analysis comparing the differential outcomes procedure to a nondifferential outcomes procedure among clinical and nonclinical populations. Sixty distinct experiments were included in the systematic review, 43 of which were included in the meta-analysis. We calculated pooled effect sizes for accuracy (overall accuracy, test accuracy, transfer accuracy) and acquisition outcomes (latency, errors, and trials to mastery). The meta-analysis revealed significant medium-to-large effect sizes for all three accuracy measures (pooled effect size range, 0.57 to 1.30). We found relatively greater effect sizes among clinical populations (effect size = 1.04). The single-subject experimental literature included in the systematic review was consistent with the findings from the group studies, demonstrating improvements in accuracy and speed of learning for the majority of participants. Moderator and subgroup analyses suggest that discrimination difficulty may induce relatively larger differential outcomes effects. The results indicate that the differential outcomes procedure can be a valuable addition to reinforcement-based interventions.