Neuroscientists studies the role of the brain chemical serotonin in aggression. One sample of rats serves as a control group and receives a placebo. 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 presented below.

a. Using a one-tailed test with = .01, decide if the drug have a significant effect on aggression.

b. Use Cohen's d to measure the effect size and interpret the size of the effect (e.g. small, medium, large).

Low Serotonin Control

n1 = 4 n2 = 8

M1 = 24 M2 = 14

SS1 = 76 SS2 = 164