simsurvdata {blapsr}R Documentation

Simulation of right censored survival times for the Cox model.

Description

Generates right censored time-to-event data. Latent event times are drawn from a Weibull distribution, while censoring times are generated from an exponential distribution.

Usage

simsurvdata(a, b, n, betas, censperc, tmax = NULL)

Arguments

a, b

The shape parameter 'a>0' and scale parameter 'b>0' of the Weibull.

n

Sample size.

betas

A numeric vector of regression coefficients. Allowed components of 'betas' are in the interval [-1 ,1] and the total number of components cannot exceed 5.

censperc

A numeric value in [0,100] corresponding to the targeted percentage of censoring.

tmax

A maximum upper bound for the generated latent event times. Especially useful for a simulation study in which the observed event times are constrained to be generated in a fixed range.

Details

The Weibull baseline hazard is parameterized as follows (see Hamada et al. 2008 pp. 408-409) :

h_0(t) = (a/(b^a)) t^(a-1), t > 0.

The ith latent event time is denoted by T_i and is generated following Bender et al. (2005) as follows:

T_i = b (-log(U_i) exp(-\beta^T x_i))^(1/a),

where U_i is a uniform random variable obtained with 'runif(1)' , x_i is the ith row of a covariate matrix X of dimension 'c(n, length(betas))' where each component is generated from a standard Gaussian distribution and \beta is the vector of regression coefficients given by 'betas'.

Value

An object of class 'simsurvdata' which is a list with the following components:

sample.size

Sample size.

censoring

Censoring scheme. Either No censoring or Exponential.

num.events

Number of events.

censoring.percentage

The effective censoring percentage.

survdata

A data frame containing the simulated data.

regcoeffs

The true regression coefficients used to simulate the data.

S0

The baseline survival function under the chosen Weibull parameterization.

h0

The baseline hazard function under the chosen Weibull parameterization.

Weibull.mean

The mean of the Weibull used to generate latent event times.

Weibull.variance

The variance of the Weibull used to generate latent event times.

The 'print' method summarizes the generated right censored data and the 'plot' method produces a graph with time on the x axis and horizontal bars on the y axis corresponding either to an event or a right censored observation. If 'n > 25', only the 25 first observations are plotted.

Author(s)

Oswaldo Gressani oswaldo_gressani@hotmail.fr.

References

Bender, R., Augustin, T. and Blettner, M. (2005). Generating survival times to simulate Cox proportional hazards models, Statistics in Medicine 24(11): 1713-1723.

Hamada, M. S., Wilson, A., Reese, C. S. and Martz, H. (2008). Bayesian Reliability. Springer Science and Business Media.

Examples

set.seed(10)
sim <- simsurvdata(a = 2, b = 1, n = 300, betas = c(0.8, -0.6), censperc = 25)
sim
plot(sim)


[Package blapsr version 0.6.1 Index]