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\name{drfit}
\alias{drfit}
\title{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{
  \item{data}{
    A data frame as returned from \code{\link{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
    \code{\link{drplot}} function, a factor called "dosefactor" also has to be
    present, containing the dose as a factor.
    }
  \item{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.}
  \item{lognorm}{
    A boolean defining if cumulative density curves of normal distributions
    are fitted to the data. Default ist TRUE.} 
  \item{logis}{
    A boolean defining if cumulative densitiy curves of logistic distributions
    are fitted to the data. Default is FALSE.} 
  \item{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.}
  \item{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{
  \item{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.}
    
} 
\examples{
\dontrun{data(antifoul)}
\dontrun{r <- drfit(antifoul)}
\dontrun{format(r,digits=2)}
}
\author{
  Johannes Ranke 
  \email{jranke@uni-bremen.de} 
  \url{http://www.uft.uni-bremen.de/chemie/ranke}
}
\keyword{models}
\keyword{regression}
\keyword{nonlinear}

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