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 18 workers is obtained. Half (n = 9) attend the workshop and the other half (n = 9) 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:
|M = 17.5||M = 22.7|
|S2 = 290||S2 = 358|
(a) Use the sample data to make a point estimate of the mean difference in confidence between the control group and the workshop conditions.
(b) Make an interval estimate of the mean difference so that you are 80% confident that the population mean difference is in your interval
( , )