In their meta-analysis of the effects of intelligent tutoring systems (ITS) on students’ mathematical learning, Steenbergen-Hu and Cooper (2013) examined results in many different categories such as math subject, ITS duration, schooling level, and research design. To calculate effect sizes, the comparison group mean was subtracted from the ITS mean and the difference was divided by the average of the two groups’ standard deviations. With respect to research design, they found that the average effect size from 15 quasi-experimental studies was .09, 95% CI (.05, .14), and the average effect size from 11 true experiments was -.01, 95% CI (-.07, .05).

1. Using Cohen’s guidelines, how would you interpret the mean effect size from quasi-experimental studies?

2. Based on the 95% CI, what would we conclude regarding the statistical significance of the quasi-experimental mean effect size?

3. Using Cohen’s guidelines, how would you interpret the mean effect size from true experiments?

4. Based on the 95% CI, what would we conclude regarding the statistical significance of the true experiment mean effect size?