Computation of t-year survival probabilities and t-year
risks with right censored survival data. The Kaplan-Meier estimator
is used to provide estimates for data without competing risks and
the Aalen-Johansen estimator is used when there are competing risks.
Confidence intervals and p-values are obtained using either usual
Wald-type inference or empirical likelihood inference, as described
in Thomas and Grunkemeier (1975)