ED {drc}R Documentation

Estimating effective doses

Description

'ED' estimates effective doses given (ECp/EDp/ICp) for given reponse levels.

Usage

  ED(object, respLev, bound = TRUE, od = FALSE, ci = c("none", "delta", "fls", "tfls"), 
  level = ifelse(!(ci=="none"), 0.95, NULL), logBase = NULL,
  reference = c("control", "upper"), type = c("relative", "absolute"), 
  display = TRUE, ...)

Arguments

object an object of class 'drc'.
respLev a numeric vector containing the response levels.
bound logical. If TRUE only ED values between 0 and 100% are allowed. FALSE is useful for hormesis models.
od logical. If TRUE adjustment for over-dispersion is used.
ci character string specifying the type of confidence intervals to be supplied. The default is "none". Use "delta" for asymptotics-based confidence intervals (using the delta method and the t-distribution). Use "fls" for from logarithm scale based confidence intervals (in case the parameter in the model is log(ED50) as for the boltzmann) models.
level numeric. The level for the confidence intervals. The default is 0.95.
logBase numeric. The base of the logarithm in case logarithm transformed dose values are used.
reference character string. Is the upper limit or the control level the reference?
type character string. Whether the specified response levels are absolute or relative (default).
display logical. If TRUE results are displayed. Otherwise they are not (useful in simulations).
... additional arguments for the function doing the calculations.

Details

This function is only implemented for the built-in functions of class 'braincousens', 'gompertz', 'logistic' and 'mlogistic'.

For objects of class 'braincousens' or 'mlogistic' the additional argument may be the 'upper' argument or the 'interval' argument. The 'upper' argument specifies the upper limit of the bisection method. The upper limit needs to be larger than the EDx level to be calculated. The default limit is 1000, but this may need to be increased. The 'interval' argument should specify a rough interval in which the dose yielding the maximum hormetical response lies. The default interval is 'c(0.001, 1000)'. Notice that the lower limit should not be set to 0 (use something like 1e-3, 1e-6, ...).

Value

A matrix with two columns: one containing the estimates and one containing the corresponding estimated standard errors.

Author(s)

Christian Ritz

See Also

The related function SI.

Examples


### How to use 'ED'

## Fitting 4-parameter log-logistic model
ryegrass.m1<-drm(ryegrass, fct=LL.4())

## Calculating EC/ED values
ED(ryegrass.m1, c(10,50,90)) 
## first column: the estimates of ED10, ED50 and ED90
## second column: the estimated standard errors 

### How to use the argument 'ci'

## Also displaying 95
ED(ryegrass.m1, c(10,50,90), ci = "delta")

## Comparing delta method and back-transformed 
##  confidence intervals for ED values

## Fitting 4-parameter log-logistic 
##  in different parameterisation (using LL2.4)
ryegrass.m2 <- drm(ryegrass, fct=LL2.4())  

ED(ryegrass.m1, c(10,50,90), ci="fls")
ED(ryegrass.m2, c(10,50,90), ci="delta")

### How to use the argument 'bound'

## Fitting the Brain-Cousens model
lettuce.m1 <- multdrc(weight ~ conc, 
data = lettuce, fct = BC.4())

### Calculating ED[-10]

# It does not work
#ED(lettuce.m1, -10)  

## Now it does work
ED(lettuce.m1, -10, bound = FALSE)  # works
ED(lettuce.m1, -20, bound = FALSE)  # works

## It does not work for another reason: ED[-30] does not exist 
#ED(lettuce.m1, -30, bound = FALSE)  


[Package drc version 1.4-2 Index]