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 the effect size?
To calculate the effect size for a t test for dependent means, we can use Cohen's d formula:
Effect size (d) = Mean difference / Standard deviation of the distribution of means
In this case, the mean difference is an increase of 5.2, and the standard deviation of the distribution of means is 2.0.
So, the effect size is calculated as:
d = 5.2 / 2.0
d ≈ 2.6
Therefore, the effect size for this t test is approximately 2.6.