getPars: Calculate location and scale parameters

In MCPMod: Design and Analysis of Dose-Finding Studies

Description

Given the baseline, the maximum effect and the standardized model parameters this function calculates the location and scale parameters in the model function using the maximum approach, see Pinheiro et al. (2006) for the basic idea.

Usage

getPars(model, doses, initEstim, base, maxEff,
        off = 0.1 * max(doses), scal = 1.2 * max(doses))

Arguments

model	A character string with the model name. Built-in models have their full parameterization derived internally. For user-defined models, it is assumed that a function named as "Par" appended to end of model name exists (e.g., for model = "cubic", it is assumed that there is function "cubicPar" that calculates the necessary parameters; this function is assumed to have arguments "doses", "initEstim", "base", and "maxEff", in that order (see below for an example).
doses	Doses to be used in design
initEstim	Vector of guesstimates
base	Expected baseline effect
maxEff	Expected maximum change from baseline
off	Offset parameter for the linear in log model (default 1).
scal	Scale parameter for the beta model (default: 20 perc. larger than maximum dose).

Value

Vector containing all model parameters.

References

Pinheiro, J. C., Bornkamp, B. and Bretz, F. (2006). Design and analysis of dose finding studies combining multiple comparisons and modeling procedures, Journal of Biopharmaceutical Statistics, 16, 639–656

See Also

fullMod

Examples

doses <- c(0, 10, 25, 50, 100, 150)                                        
getPars("emax", doses, 25, 0, 0.4)                                         
getPars("logistic", doses, c(50, 10.88111), 0, 0.4) # compare JBS 16, p.650
getPars("betaMod", doses, initEstim = c(0.33, 2.31), base = 0,             
        maxEff = 0.4)                                                      
#example for user model                                                    
userMod <- function(dose, e0, eMax, ed50, h){                             
  e0 + eMax * ( dose^h / (ed50^h + dose^h) )                               
}                                                                          
# function to return location and scale parameters                         
userModPar <- function(dose, initEstim, base, maxEff){                    
  # function to get linear parameters                                      
  # ed50 parameter assumed to be first in initEstim                        
  ed50 <- initEstim[1]                                                     
  h <- initEstim[2]                                                        
  dmax <- max(dose)                                                        
  emax <- maxEff*(ed50^h+dmax^h)/dmax^h                                    
  c(base, emax, initEstim)                                                 
}                                                                          
getPars("userMod", doses, initEstim = c(50,2), base = 0, maxEff = 1) 

MCPMod documentation built on March 26, 2020, 7:28 p.m.