1. Describe the data that are collected for an independent-measures t test and the hypotheses that the test evaluates.

2. 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.

Control Low Serotonin

n = 10 n = 15

M = 14 M = 19

SS = 180.5 SS = 130.0

a. Does the drug have a significant effect on aggression? Use an alpha level of .05, two tails.

b. Compute Cohen's d to measure the size of the treatment effect.

4. The following data are from an independent-measures experiment comparing two treatment conditions. Treatment 1 Treatment 2

4 19

5 11

12 18

10 10

10 12

7 14

a. Do these data indicate a significant difference between the treatments at the .05 level of significance?

b. Compute r2 to measure the size of the treatment effect.

c. a sentence demonstrating how the outcome of the hypothesis test and the measure of effect size would appear in a research report.

5. A major company would like to assess the impact of using a professional trainer to conduct a confidence-building workshop with their salespeople. A sample of 16 workers is obtained. Half (n = 8) attend the workshop and the other half (n = 8) serves as a control group. Two weeks later, each of the participants is given a questionnaire measuring the level of self-confidence. The data are as follows:

Controls Workshop

M = 17.5 M = 22.7

SS = 100 SS = 124

Use the sample data to construct an 80% confidence interval for the mean difference in confidence between the control group and the workshop conditions.