Calculate a standardized effect size, Cohen’s d, for the data given in Exercise 3. Interpret this effect size using Cohen’s guidelines which are provided in your textbook.

Data from exercise 3

Willoughby, Porter, Belsito, and Yearsley (1999) investigated the effectiveness of special study strategies among elementary school children for the task of learning factual information about unfamiliar animals. Their study included three grade levels and three treatment conditions. Summary information for only the fourth and sixth graders in the keyword strategy condition is presented in this exercise. The mean memory test performance of the 15 fourth graders was 8.20, with SS equal to 102.06. The mean memory test performance of the 15 sixth graders was 10.73, with SS equal to 168.57. Was there a significant difference between the memory performance of the fourth and sixth graders? Follow the steps below to answer this question. Designate the fourth graders as group 1 and the sixth graders as group 2.