Dr. Zak developed a test to measure depression. He sampled 100 university students to take his five item test. The group of students was comprised of 30 men and 70 women. In this group, four persons were African American, six persons were Hispanic, and one person was Asian. Zak's Miraculous Test of Depression is printed below:
The mean on this test is 3.5 with a standard deviation of .5.
1. I feel depressed: Yes No
2. I have been sad for the last two weeks: Yes No
3. I have seen changes in my eating and sleeping: Yes No
4. I don't feel that life is going to get better: Yes No
5. I feel happy most of the day: Yes No
Yes = 1; No = 0
The mean on this test is 3.5 with a standard deviation of .5.
Follow-Up Questions
1. Sally scores 1.5 on this test. How many standard deviations is Sally from the mean? (Show your calculations)
2. Billy scores 5. What is his standard score?
3. What scale of measurement is Dr. Zak using? Do you think Dr. Zak's choice of scaling is appropriate? Why or why not? What are your suggestions?
4. Do you think Dr. Zak has a good sample on which to norm his test? Why or why not? What are your suggestions?
5. What other items do you think need to be included in Dr. Zak's domain sampling?
6. Suggest changes to this test to make it better. Justify your reason for each suggestion supporting each reason with psychometric principles from the text book or other materials used in your course.
7. Dr. Zak also gave his students the Beck Depression Inventory (BDI). The correlation between his test and the BDI was r =.14. Evaluate this correlation. What does this correlation tell you about the relationship between these two instruments?