timeEL (version 0.9.1)

TwoSampleKaplanMeier: Risk difference and risk ratio using the Kaplan-Meier method

Description

Computes a risk difference, risk ratio or survival ratio with right-censored data, together with a confidence interval and a p-value (to test for a difference between two groups). Pointwise estimates are computed via the Kaplan-Meier estimator. Computation of confidence intervals and p-values are based on either Empirical Likelihood (EL) inference or Wald-type inference. Both are non-parametric approaches, which are asymptotically equivalent. See Thomas & Grunkemeier (1975) for details about the Empirical Likelihood method. For the Wald-type approach, the asymptotic normal approximation is used on the log scale for the risk ratio or survival ratio. No transformation is used for the risk or survival difference.

Usage

TwoSampleKaplanMeier(
  time,
  status,
  group,
  t,
  SR.H0 = 1,
  RR.H0 = 1,
  Diff.H0 = 0,
  level = 0.95,
  contr = list(tol = 1e-05, algo = 2, k = 3, Trace = FALSE, method = "both")
)

Value

an object of class 'TwoSampleKaplanMeier'

Arguments

time

vector of times (possibly censored)

status

vector of usual survival status indicators (0 for censored observations, 1 otherwise)

group

vector of binary group indicator. The reference group should be coded 0, the other 1.

t

the time point of interest (e.g. 1 to compute 1-year risk ratio)

SR.H0

the survival ratio under the null hypothesis, to compute a p-value. Default is 1.

RR.H0

the risk ratio under the null hypothesis, to compute a p-value. Default is 1.

Diff.H0

the risk difference under the null hypothesis, to compute a p-value. Default is 0.

level

confidence level for the confidence intervals. Default is 0.95.

contr

list of control parameters. tol=tolerance for numerical computation, default is 1e-5. method="EL", "Wald" or "both" indicates wether 95% CI and the p-value should be computed based on Empirical Likelihood inference, Wald-type inference or both. algo=2 is currently the only option that is implemented.

Author

Paul Blanche

References

Thomas & Grunkemeier (1975). Confidence interval estimation of survival probabilities for censored data. Journal of the American Statistical Association, 70(352), 865-871.

Examples

# This example reproduces some results presented in Table 4 of Thomas and Grunkemeier (1975)
Res2SKM95 <- TwoSampleKaplanMeier(time=Freireich$time,
                                  status=Freireich$status,
                                  group=Freireich$group,
                                  t=10)
Res2SKM95