Why should we perform an effect size equation for our data? a. it does not include the n and so it gives a true idea of how large the difference is between the group means b. it does not include the n, and so it gives a true idea of how large the variance is between the group means c. it includes the n, and so it gives a true idea of how large the difference is between the group means d. it includes the n, and so it gives a true idea of how large the variance is between the group means