A biopsychologist 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. She expects that the reduction in serotonin will result in an increase in aggressive behaviors. The data are presented below. Use a one-tailed test at the .05 level of significance.

Low Serotonin Control / Placebo

n1 = 4 n2 = 8

M1 = 22 M2 = 14

SS1 = 76 SS2 = 164

A - Which t statistic, (single-sample, independent-measures, or repeated-measures), should be used with this data?

B - State the H0 and H1 in symbols. [Hint: one-tailed test]

C - State the t-score value that defines the critical region(s).

D - Report the variance, estimated standard error and obtained t-statistic value.

E - State the decision that should be made based on these results.

F - Write the results / decision in apa symbols.

G - State the decision that would be made at the = .01 level of significance, one-tailed.