Rat treatment data from Mantel et al. Three rats were chosen from each of 100 litters, one of which was treated with a drug, and then all followed for tumor incidence.
rats data(cancer, package="survival")
|litter:||litter number from 1 to 100|
|time:||time to tumor or last follow-up|
|status:||event status, 1=tumor and 0=censored|
|sex:||male or female|
E. W. Lee, L. J. Wei, and D. Amato, Cox-type regression analysis for large number of small groups of correlated failure time observations, in "Survival Analysis, State of the Art", Kluwer, 1992.