A professor wants to compare the test scores of his two psychology classes (Class A and Class B). Each class has 20 students. The professor calculates a t value of 2.3 and concludes that Class B has a mean test score that is significantly higher than Class A. What is the effect size associated with this statistical test?
A) .12
B) .24
C) .35
D) .48

Question

Quizplus · Accepted Answer

To calculate effect size, we need the standardized mean difference (d) which can be calculated using the formula: 
d = t / sqrt(n1+n2 / n1*n2 + (t^2 / df))
where n1 and n2 are the sample sizes of Class A and Class B, and df is the degrees of freedom (n1 + n2 - 2). 
Substituting the values given, we get: 
d = 2.3 / sqrt(20+20 / 20*20 + (2.3^2 / 38)) = 0.35. 
Therefore, the effect size associated with this statistical test is 0.35, which corresponds to choice C.

A Professor Wants to Compare the Test Scores of His