A researcher reports that the mean difference in the body weight of rats following a pharmacological versus control treatment is 14 grams,with a pooled sample variance equal to 256.What is the effect size for this test using estimated Cohen's d?
A)d = 0.06;small effect size
B)d = 0.08;small effect size
C)d = 0.88;large effect size
D)There is not enough information to answer this question.

Question

Quizplus · Accepted Answer

Cohen's d can be calculated using the formula: d = (mean difference) / (pooled standard deviation). 
In this case, the mean difference is 14 grams and the pooled standard deviation is the square root of the pooled sample variance, which is 16. 
Therefore, d = 14 / 16 = 0.88. 
According to Cohen's guidelines for effect size, a d of 0.2 is considered a small effect, 0.5 is considered a medium effect and 0.8 or higher is considered a large effect. As the calculated d is 0.88, this would be considered a large effect size.

A Researcher Reports That the Mean Difference in the Body