A researcher reports that the mean difference in the body weight of rats following a pharmacological versus control treatment is 14 g,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

To calculate Cohen's d, we need to divide the mean difference by the square root of the pooled sample variance, which is the square root of 256 or 16. 
d = 14/16 
d = 0.875 
This indicates a large effect size according to Cohen's guidelines, which state that effect sizes of 0.2, 0.5, and 0.8 represent small, medium, and large effects, respectively. Therefore, the correct answer is C.

A Researcher Reports That the Mean Difference in the Body