Researchers wanted to explore self-esteem in adolescent boys and adolescent girls. They used a 5-point Likert-type self-esteem inventory; a 1 = strongly disagree and 5 = strongly agree. Their results yielded the following t = 1.71 and d = 0.90.

What statistical test did the researchers use to determine if there was a statistically significant difference in levels of self-esteem between boys and girls? What was the purpose of calculating a Cohen's d? When is a Cohen's d calculated? Interpret d=0.90. What does it mean in this example? What if the researcher compared the adolescent boys before treatment and again after treating them for depression? What type of t-test would be appropriate in this case, and why?