getn {dfcrm}

Sample size calculator for CRM trials

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, \beta) = d^{\exp(\beta)}, where \beta 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