computeLogrankZ: Helper function to computes the logrank statistic for 'Surv'...

In safestats: Safe Anytime-Valid Inference

Helper function to computes the logrank statistic for 'Surv' objects of type "right" and "counting" with the hypergeometric variance.

Description

This function was created to complement survdiff from the 'survival' package, which is restricted to 'Surv' objects of type "right". Most likely survdiff is much faster

Usage

computeLogrankZ(
  survObj,
  group,
  computeZ = TRUE,
  computeExactE = FALSE,
  theta0 = 1,
  thetaS = NULL,
  ...
)

Arguments

survObj	a Surv object that is either of type
group	a grouping factor with 2 levels
computeZ	logical. If TRUE computes the logrank z-statistic. Default is TRUE.
computeExactE	logical. If TRUE computes one-sided exact logrank e-value. Default is FALSE.
theta0	numeric > 0 used only for the e-value, i.e., if computeExactE is TRUE. Default is 1.
thetaS	numeric > 0 used only for the e-value, i.e., if computeExactE is TRUE. Default is NULL.
...	further arguments to be passed to or from methods.

Value

Returns a list containing at least the following components:

nEvents

the number of events.

z

the observed logrank statistic.

oMinEVector

vector of observed minus expected.

varVector

vector of hypergeometric variances.

stopTimeVector

vector at which the events occurred.

References

Grünwald, P. D., de Heide, R., & Koolen, W. (2024). Safe testing. Journal of the Royal Statistical Society. Series B (Methodological), 86(5), 1091-1128. (With discussions), https://doi.org/10.1093/jrsssb/qkae011. ter Schure, J., Pérez-Ortiz, M. F., Ly, A., & Grünwald, P. D. (2024). The Safe Logrank Test: Error control under continuous monitoring with unlimited horizon. The New England Journal of Statistics in Data Science, 2(2), 190-214, https://doi.org/10.51387/24-NEJSDS65. Schoenfeld, D. (1981). The asymptotic properties of nonparametric tests for comparing survival distributions. Biometrika, 68(1), 316-319, https://doi.org/10.2307/2335833.

Examples

data <- generateSurvData(nP = 5,
                         nT = 5,
                         lambdaP = 0.03943723,
                         lambdaT = 0.5*0.03943723,
                         endTime = 40,
                         seed = 2006)

survObj <- survival::Surv(data$time, data$status)

survObj <- survival::Surv(data$time, data$status)

result <- computeLogrankZ(survObj, data$group)
result$z
sqrt(survival::survdiff(survObj~data$group)$chisq)

safestats documentation built on Sept. 6, 2026, 1:06 a.m.