A professor computes the mean difference in exam scores before and after a lecture as 9.0 ± 14.5 (M_D± S_D),and this difference was significant.What is the effect size for this result using estimated Cohen's d? A) d = 0.62 (medium effect) B) d = 1.61 (medium effect) C) d = 0.62 (large effect) D) d = 1.61 (large effect)

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Quizplus · Accepted Answer

Cohen's d is calculated as the mean difference divided by the standard deviation. Here, d = 9.0 / 14.5 = 0.62. According to Cohen's conventions, 0.2 to 0.5 is a small effect, around 0.5 is a medium effect, and 0.8 and above is a large effect. Therefore, 0.62 is considered a medium effect.

A Professor Computes the Mean Difference in Exam Scores Before