Suppose the investigator referred to in Exercise 15.9 decided that instead of running one group and comparing it against µ 0 = 5.8, she would run two groups (one with and one without lesions). She would still expect the same degree of difference, however.
(a) How many subjects does she now need (overall) if she is to have power equal 0.60?
(b) How many subjects does she now need (overall) if she is to have power equal 0.90?