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.
How many rats had tumors? What was the total rat-time contributed by all the animals? What was the incidence rate for tumors?
Calculate a Wald 95% confidence interval for the true incidence rate λ