A researcher computes the mean difference in locomotion in a sample of 12 rats before and 30 minutes after an injection of amphetamine. Rats were placed in a box with infrared beams. The number of times rats crossed the beams was used as a measure of locomotion. The mean difference in locomotion was
6.2 ± 8.4 (MD ± SD), and this difference was significant. What is the effect size for this result using estimated Cohen's d?
a. d = 0.74 (medium effect)
b. d = 1.36 (medium effect)
c. d = 0.74 (large effect)
d. d = 1.36 (large effect)
Answer: A
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