drfit(drfit)R Documentation

Fit dose-response models

Description

Fit dose-response relationships to dose-response data and calculate biometric results for (eco)toxicity evaluation

Usage

  drfit(data, startlogEC50 = NA, lognorm = TRUE, logis = FALSE, 
    linearlogis = FALSE, b0 = 2, f0 = 0)

Arguments

data A data frame as returned from drdata. The data frame has to contain at least a factor called "substance", a vector called "unit" containing the unit used for the dose, a column "response" with the response values of the test system normalized between 0 and 1 and a column "dose" with the numeric dose values. For later use of the drplot function, a factor called "dosefactor" also has to be present, containing the dose as a factor.
startlogEC50 Especially for the linearlogis model, a suitable log10 of the EC50 has to be given by the user, since it is not correctly estimated for data showing hormesis with the default estimation method.
lognorm A boolean defining if cumulative density curves of normal distributions are fitted to the data. Default ist TRUE.
logis A boolean defining if cumulative densitiy curves of logistic distributions are fitted to the data. Default is FALSE.
linearlogis A boolean defining if the linear-logistic function as defined by van Ewijk and Hoekstra 1993 is fitted to the data. Default is FALSE.
b0,f0 If the linearlogistic model is fitted, b0 and f0 give the possibility to adapt the starting values for the parameters b and f.

Value

results A data frame containing at least one line for each substance. If the data did not show a mean response < 0.5 at the highest dose level, the modeltype is set to "none". Every successful fit is reported in one line. Parameters of the fitted curves are only reported if the fitted EC50 is not higher than the highest dose.

Author(s)

Johannes Ranke jranke@uni-bremen.de http://www.uft.uni-bremen.de/chemie/ranke

Examples

data(antifoul)
r <- drfit(antifoul)
format(r,digits=2)
[Package Contents]