Instructions: The rats data set in the survival package in R can be loaded by typing data(rats).

Instructions: The rats data set in the survival package in R can be loaded by typing

"data(rats)". It contains data on 300 rats—3 selected from each of 100 litters—that were followed for tumor incidence. The variable time is the

follow-up times and the variable status is the event indicator.

Questions:Calculate a log-transformed 95% confidence interval for λ.

1. Use the function survreg to fit an exponential distribution and calcu- late the 95% confidence interval for λ. Does it agree with the Wald or log-transformed confidence intervals?
2. Fit a Weibull distribution and get point estimates and 95% confidence intervals for the rate and shape parameters. Is the exponential distribution a good model for this data?