A random sample of 25 third graders scored an average of 3.4 on a standardized reading test. The standard deviation was 0.95. A test is conducted to determine if the mean score is significantly higher than 3. What is the effect size of this test?
A) 0.42
B) 2.11
C) 3.16
D) None of the above

Question

Quizplus · Accepted Answer

The effect size can be calculated using Cohen's d, which is the difference between the mean score and the hypothesized mean, divided by the standard deviation: $d = \frac{\bar{x} - \mu}{s} = \frac{3.4 - 3}{0.95} = \frac{0.4}{0.95} = 0.42$.

A Random Sample of 25 Third Graders Scored an Average