getn: Sample size calculator for CRM trials

In dfcrm: Dose-Finding by the Continual Reassessment Method

Description

Sample size calculator for a one-stage Bayesian CRM (see Details for design specification).

Usage

getn(apcs, target, nlevel, psi, correction = TRUE, detail = FALSE)

Arguments

apcs	The desired average probability of correction selection (PCS) under the logistic calibration set.
target	The target DLT rate.
nlevel	The number of test doses.
psi	Effect size, i.e., odds ratio of the logistic dose-toxicity curves.
correction	Continuity correction is applied in the sample size calculation if TRUE (default). Otherwise if FALSE.
detail	Print only essential results for trial planning if FALSE (default). Otherwise if TRUE.

Details

The sample size calculation is based on empirical approximation for the CRM using the power (or empiric) dose-toxicity function, F(d, β) = d^{\exp(β)}, where β has a normal prior with mean 0 and variance 1.34, and the starting dose is the median level. The “skeleton" is obtained by setting halfwidth at 0.25 \times target, and nu at the median level in the function getprior.

The calculation is intended to serve as an initial sample size for the CRM calibration process depicted in Figure 7.1 in Cheung (2011).

Value

An object of class “crmsize" is returned, consisting of the following components:

n	The calculated sample size.
astar	The desired average PCS.
target	The target DLT rate.
nlevel	The number of test doses.
psi	Odds ratio.
bstar	An intermediate value used to calculate the sample size. Shown only if detail=TRUE.
efficiency	Ratio of required sample sizes of the optimal benchmark and the CRM. Shown only if detail=TRUE.
correction	Whether continuity correction is applied. Shown only if detail=TRUE.
na	The CRM sample size before rounding up.
nb	The sample size lower bound before rounding up.
messages	String characters prompt warning messages and caveats regarding the sample size calculation.

References

Cheung, Y. K. (2011). Dose Finding by the Continual Reassessment Method. New York: Chapman & Hall/CRC Press.

See Also

getprior

Examples

apcs <- 0.6    
target <- 0.25
nlevel <- 5
psi <- 1.8     

# Sample size calculation with continuity correction
obj = getn(apcs, target, nlevel, psi, correction=TRUE)
obj

N = obj$n

Example output

 Target rate:			 0.25 
 Number of dose levels:		 5 
 Effect size (odds ratio):	 1.8 
 Required accuracy:		 0.6 
 Calculated sample size:	 32 

dfcrm documentation built on May 1, 2019, 10:18 p.m.