Consider the following two statements.

(i) “The level of aluminum in the brain is higher in patients with Alzheimer’s disease than in other people.”

(ii) “The ‘Alzheimer Severity Index,’ which measures the seriousness of Alzheimer’s disease, is related to the level of aluminum in the brain.”

a) Is the correlation coefficient a useful measure of the extent of the relationship in statement (i)? State your reasons clearly.

b) Is the correlation coefficient a useful measure of the extent of the relationship in statement (ii)? State your reasons clearly.

c) What assumption would you need to make before using the correlation coefficient in this way?