Glass's Delta is a statistical measure used in the field of psychology and education to assess the effectiveness of interventions or treatments. It quantifies the difference in performance between two groups, typically a treatment group and a control group, by calculating the effect size. This helps researchers understand how significant the impact of an intervention is compared to no intervention. The formula for Glass's Delta involves dividing the difference in means of the two groups by the standard deviation of the control group. This approach is particularly useful when the control group is more stable, providing a clearer picture of the treatment's effectiveness.