Question: Researchers have always been interested in the neuromodulation of immune function. Irwin and colleagues (1987) published results of a study that investigated the relationship between stressful major life events and immune function. Subjects in the study were women who husbands were undergoing treatment for metastatic lung cancer, women whose husbands had died of lung cancer 1 to 6 months prior to the study, and women whose husbands were in good health. Scores on the Social Readjustment Rating Scale (SRRS) were recorded for each woman. According to their scores on the Social Readjustment Scale, the women were divided into three groups: those with low scores (≤ 54), those with moderate scores (55-99), and those with high scores (≥ 100). The researchers want to determine whether the mean level of natural killer cell activity differs between the groups.

a) State the null and alternative hypotheses. What assumptions are necessary to perform this test?

b) Perform the appropriate statistical test using a =. 05 and check the assumptions. Provide all outputs required to check assumption.

c) Perform pairwise comparisons of the groups means using the Bonferroni method.

d) Are you confident the assumptions hold? Explain. In light of your opinion, interpret the results.

e) The output below is from an appropriate non-parametric test to test whether the median cell activity levels differ? Do these results strengthen or weaken you convictions about the conclusion you drew in part d)? Explain.