The graphs show standard error, not standard deviation. Standard error is standard deviation divided by the square root of the sample size. It’s included on graphs to show which differences are statistically significant—it does not give a sense of the variability within a group.
Cohen’s d counts standard deviations (d=.18 means that the two means are .18 standard deviations apart), so there is actually a lot of overlap between the groups.
The graphs show standard error, not standard deviation. Standard error is standard deviation divided by the square root of the sample size. It’s included on graphs to show which differences are statistically significant—it does not give a sense of the variability within a group.
Cohen’s d counts standard deviations (d=.18 means that the two means are .18 standard deviations apart), so there is actually a lot of overlap between the groups.