A researcher conducts an independent-measures study examining how the brain chemical serotonin is related to aggression. One sample of rats serves as a control group and receives a placebo that does not affect normal levels of serotonin. A second sample of rats receives a drug that lowers brain levels of serotonin. Then the researcher tests the animals by recording the number of aggressive responses each of the rats display. The data are as follows.
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Control
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Low Serotonin
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n = 10
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n = 15
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xbar = 14
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xbar = 19
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SS = 180.5
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SS = 130
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a) Does the drug have a significant effect on aggression? Use Alpha = .05.
b) What is Cohen's d?