Most major corporations have psychologists available to help employees who suffer from stress. One problem that is difficult to diagnose is post-traumatic stress disorder (PTSD). Researchers studying PTSD often use as subjects former prisoners of war (POWs).

Psychological Assessment (Mar. 1995) published the results of a study of World War I1 aviators who were captured by German forces after they were shot down.

Having located a total of 239 World War I1 aviator POW survivors, the researchers asked each veteran to participate in the study; 33 responded to the letter of invitation. Each of the 33 POW survivors was administered the Minnesota Multiphasic Personality Inventory, one component of which measures level of PTSD.

[Note: The higher the score, the higher the level of PTSD.] The aviators produced a mean PTSD score of -

x = 9.00 and a standard deviation of s = 9.32.

a. Set up the null and alternative hypotheses for determining whether the true mean PTSD score of all World War I1 aviator POWs is less than 16. [Note:

The value, 16, represents the mean PTSD score established for Vietnam POWs.]

b. Conduct the test, part

a, using a = .lo. What are the practical implications of thc test?

c. Discuss the representativeness of the sample used in the study and its ramifications.