A researcher conducts a t test for dependent means in which it is predicted that there will be a decrease in unemployment from before to after a particular job-skills training program. The cutoff "t" needed is -1.8333. The standard deviation of the distribution of means of change scores is 2.0 and the mean change score for the sample studied is an increase of 5.2.
What is considered a medium effect size for a t test for dependent means?
To determine what is considered a medium effect size for a t test for dependent means, we need to calculate Cohen's d. Cohen's d is a standard measure of effect size that helps quantify the magnitude of the difference between two groups.
The formula to calculate Cohen's d for a t test for dependent means is:
Cohen's d = mean difference / standard deviation of the difference scores
Given the information provided:
Mean difference = 5.2 (increase of 5.2)
Standard deviation of the difference scores = 2.0
Cohen's d = 5.2 / 2.0 = 2.6
Typically, in the context of a t test for dependent means, a medium effect size is considered to be around 0.5. Therefore, in this case, a Cohen's d value of 2.6 would be considered a large effect size, indicating a substantial difference between the groups.