cohere {titecrm}R Documentation

Coherence of Two-stage CRM

Description

Returns a message on the coherence status of a two-stage CRM design.

Usage

cohere(prior, target, n, x0, method="bayes", scale=sqrt(1.34), detail=TRUE)

Arguments

prior A vector of initial estimates of toxicity probabilities associated the doses.
target The target DLT rate.
n Sample size of the trial.
x0 A vector of treatment sequence according to the initial design. Must be of length n.
method A character string to specify the method for parameter estimation. The default method ``bayes'' estimates the model parameter by the posterior mean. Estimation using ``mle'' is to be made available.
scale Standard deviation of the normal prior of the model parameter. Default is sqrt(1.34).
detail If TRUE, details about incoherent escalations will be displayed.

Details

Dose-toxicity relationship is assumed as an empiric power model $a_i^{exp(β)}$ where $a_i$ is the initial estimate of toxicity probability of dose level i and the model parameter $β$ has a normal prior with mean 0 and scale to be provided by users.

A two-stage CRM is defined by two components. First, an initial design sequence (x0) for dose assignments before any DLT is seen. When a DLT is seen, dose assignment decisions are switched to the CRM. See Cheung (2005) in the reference section.

Value

A string character giving a message on the coherence status of a two-stage CRM design.

References

Cheung, Y. K. and Chappell, R. (2000). Sequential designs for phase I clinical trials with late-onset toxicities. Biometrics 56:1177-1182.

Cheung, Y. K. (2005). Coherence principles in dose-finding studies. Biometrika 92:863-873.

Examples

# Create a simple data set
prior <- c(0.05,0.10,0.20,0.35,0.50,0.70)
target <- 0.2
n <- 24
x0 <- c(rep(1,3),rep(2,3),rep(3,3),rep(4,3),rep(5,3),rep(6,9))
# The above design is coherent
foo <- cohere(prior,target,n,x0)
print(foo)

# The design is incoherent if a larger target DLT rate is used.
target2 <- 0.3
foo2 <- cohere(prior,target2,n,x0)

[Package titecrm version 0.1-1 Index]