logistic {drc}R Documentation

The logistic model

Description

The general asymmetric five-parameter logistic model for describing dose-response relationships.

Usage

  logistic(fixed = c(NA, NA, NA, NA, NA), names = c("b", "c", "d", "e", "f"), fctName, fctText) 

  L.3(fixed = c(NA, NA, NA), names = c("b", "d", "e"))
  L.4(fixed = c(NA, NA, NA, NA), names = c("b", "c", "d", "e"))
  L.5(fixed = c(NA, NA, NA, NA, NA), names = c("b", "c", "d", "e", "f"))  

  boltzmann(fixed = c(NA, NA, NA, NA, NA), names = c("b", "c", "d", "e", "f"), fctName, fctText)

  B.3(fixed = c(NA, NA, NA), names = c("b", "d", "e"))
  B.4(fixed = c(NA, NA, NA, NA), names = c("b", "c", "d", "e"))
  B.5(fixed = c(NA, NA, NA, NA, NA), names = c("b", "c", "d", "e", "f"))  

Arguments

fixed numeric vector. Specifies which parameters are fixed and at what value they are fixed. NAs for parameter that are not fixed.
names a vector of character strings giving the names of the parameters (should not contain ":"). The order of the parameters is: b, c, d, e, f (see under 'Details').
fctName optional character string used internally by convenience functions.
fctText optional character string used internally by convenience functions.

Details

The default arguments yields the five-parameter logistic mean function given by the expression

f(x) = c + frac{d-c}{(1+exp(b(x - e)))^f}

The model is different from the log-logistic models llogistic and llogistic2 where the term

log(x)

is used instead of

x

.

The model is sometimes referred to as the Boltzmann model.

Value

The value returned is a list containing the nonlinear function, the self starter function and the parameter names.

Author(s)

Christian Ritz

Examples


## Fitting the four-parameter logistic model
ryegrass.m1 <- drm(rootl ~ conc, data = ryegrass, fct = L.4())
summary(ryegrass.m1)

## Fitting an asymmetric logistic model
##  requires installing the package 'NISTnls'
# Ratkowsky3.m1 <- drm(y~x, data = Ratkowsky3, 
# fct = L.5(fixed = c(NA, 0, NA, NA, NA)))
# plot(Ratkowsky3.m1)
# summary(Ratkowsky3.m1)  
## okay agreement with NIST values
##  for the two parameters that are the same


[Package drc version 1.6-1 Index]