nevents.cure: Calculates the expected number of events for cure rate...
In raredd/desmon: Functions for design and monitoring of clinical trials

nevents.cure

R Documentation

Calculates the expected number of events for cure rate failure models

Description

Given a uniform accrual period, specified accrual rate and follow-up period, and specified parameters for the exponential cure rate failure model, computes the expected number of failures

Usage

nevents.cure(
  acc.rate,
  acc.per,
  add.fu,
  cure.rate,
  haz = NULL,
  med = NULL,
  haz.ratio = 1
)

Arguments

`acc.rate`	The accrual rate in patients per time unit
`acc.per`	Duration of accrual
`add.fu`	Duration of follow-up from end of accrual to analysis
`cure.rate`	Proportion cured
`haz`	Exponential hazard rate for failure times for those not cured. Not needed if `med` is specified.
`med`	Median failure time for those not cured. Not needed if `haz` is specified.
`haz.ratio`	Proportional hazards shift from the exponential cure rate model

Details

The exponential cure rate model has survivor function S(t) equal to p+(1-p)*exp(-l*t), where p = cure.rate and l = haz. haz and med are related through haz=log(2)/med. Optionally, a proportional hazards shift from the cure rate model with survivor function given by (p+(1-p)*exp(-l*t))^a, where a = haz.ratio, can be used by specifying a value for haz.ratio. The calculations assume that n=acc.rate*acc.per patients are entered uniformly over the period [0,acc.per], with follow-up continuing for an addition add.fu time units, so censoring will be uniform on [add.fu,add.fu+acc.per]. The failure probability under the specified failure distribution is then computed, as is the expected number of failures, n*fail.prob.

Caution: consistent time units must be used for all quantities.

Value

A vector of length 3 giving the expected number of failures nevents, the failure probability fail.prob and the total sample size n.

Examples

acc.per <- 2.2
add.fu <- 3.2
nevents.cure(240,acc.per,add.fu,cure.rate=.38,med=1.7)
nevents.cure(240,acc.per,add.fu,cure.rate=.38,med=1.7,haz.ratio=.667)

raredd/desmon documentation built on May 7, 2024, 3:46 p.m.