64. The article “Increases in Steroid Binding Globulins Induced by Tamoxifen in Patients with Carcinoma of the Breast”

(J. Endocrinology, 1978: 219–226) reports data on the effects of the drug tamoxifen on change in the level of cortisolbinding globulin (CBG) of patients during treatment. With age
x and CBG
y, summary values are n
26,
xi

1613,
(xi  x

)2
3756.96,
yi
281.9,
(yi  y

)2

465.34, and
xi yi
16,731.

a. Compute a 90% CI for the true correlation coefficient .

b. Test H0: 
.5 versus Ha:   .5 at level .05.

c. In a regression analysis of y on x, what proportion of variation in change of cortisol-binding globulin level could be explained by variation in patient age within the sample?

d. If you decide to perform a regression analysis with age as the dependent variable, what proportion of variation in age is explainable by variation in CBG?