Use the data from Practice Problem 7 to solve this problem.

a. Test whether mean PLP1 gene expression differs among the schizophrenia, bipolar, and control groups.

b. What are your assumptions in part (a)?

c. Is the analysis in part (a) a random-effects or fixed-effects ANOVA? Explain.

d. What quantity would you use to describe the fraction of the variation in expression levels explained by group differences? Calculate this quantity for the data from Practice Problem 7.

e. What method would you use after ANOVA to determine which group means were different from each other?

Data from problem 7

Finding the causes of the major mental illnesses, schizophrenia and bipolar disorder, is a major activity in medical research. Tkachev et al. (2003) compared expression levels of several genes involved in the production and activity of myelin, a tissue important in nerve function, in the brains of 15 persons with schizophrenia, 15 with bipolar illness, and 15 control individuals. The results presented in the table at the bottom of this page summarize the expression levels of the proteolipid protein 1 gene (PLP1) in the 45 brains.