In this problem we are trying to estimate the survival of liver transplant patients using information on the patients collected before the operation. The variables are:
CLOT: a measure of the clotting potential of the patient’s blood,
PROG: a subjective index of the patient’s prospect of recovery,
ENZ: a measure of a protein present in the body,
LIV: a measure relating to white blood cell count and the response, and
TIME: a measure of the survival time of the patient.
The data are given in Table 8.31.
(a) Perform a linear regression for estimating survival times. Plot residuals. Interpret and critique the model used.
(b) Because the distributions of survival times are often quite skewed, a logarithmic model is often used for such data. Perform the regression using such a model. Compare the results with those of part (a).