8.51 Effect size and English-language tests for international students: In the two previous exercises, we considered the IELTS listening module, for which the population of all IELTS takers in a year had a mean score of 6.00 with a standard deviation of 1.30 (2013). A sample of 63 international students at the University of Melbourne had mean IELTS listening scores of 7.087 with a standard deviation of 0.754 (O’Loughlin & Arkoudis, 2009).

a. Calculate the appropriate measure of effect size for this sample.

b. Based on Cohen’s conventions, is this a small, medium, or large effect?

c. Why is it useful to have this information in addition to the results of a hypothesis test?