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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, startlogED50 = NA, chooseone = TRUE, probit = TRUE, logit = FALSE,
  weibull = FALSE, linlogit = FALSE, conf = FALSE, linlogitWrong = NA,
  allWrong = NA, s0 = 0.5, b0 = 2, f0 = 0)
}
\arguments{
  \item{data}{
    A data frame containing dose-response data. The data frame has to contain
    at least a factor called \dQuote{substance}, a numeric vector \dQuote{dose}
    with the dose values, a vector called \dQuote{unit} containing the unit
    used for the dose and a numeric vector \dQuote{response} with the response
    values of the test system normalized between 0 and 1. Such a data frame can
    be easily obtained if a compliant RODBC data source is available for use in
    conjunction with the function \code{\link{drdata}}.

    If there is a column called \dQuote{ok} and it is set to \dQuote{no fit} in
    a specific line, then the corresponding data point will be excluded from
    the fitting procedure, although it will be plotted.}
  \item{startlogED50}{
    Especially for the linlogit model, a suitable log10 of the ED50 has to be
    given by the user, since it is not correctly estimated for data showing
    hormesis with the default estimation method.}
  \item{probit}{
    A boolean defining if cumulative density curves of normal distributions
    \code{\link{pnorm}} are fitted against the decadic logarithm of the dose.
    Default ist TRUE.} 
  \item{logit}{
    A boolean defining if cumulative density curves of logistic distributions
    \code{\link{plogis}} are fitted to the decadic logarithm of the dose.
    Default is FALSE.} 
  \item{weibull}{
    A boolean defining if the cumulative density curves of weibull distributions
    (\code{\link{pweibull}} with additionall location parameter and scale=1)
    are fitted to the decadic logarithm of the dose. Default is FALSE.}
  \item{linlogit}{
    A boolean defining if the linear-logistic function
    \code{\link{linlogitf}} as defined by van Ewijk and Hoekstra 1993 is
    fitted to the data. Default is FALSE.}
  \item{conf}{
    A boolean defining if a confidence interval of the log ED50 is to be
    listed for alpha = 5 \% (two-sided). If FALSE (default), the standard
    deviation is listed in the output of drfit.}
  \item{linlogitWrong}{
    An optional vector containing the names of the substances for which the
    linlogit function produces a wrong fit.}
  \item{allWrong}{
    An optional vector containing the names of the substances for which all
    functions produce a wrong fit.}
  \item{chooseone}{
    If TRUE (default), the models are tried in the order linlogit, probit,
    logit, weibull, and the first model that produces a valid fit is used.
    If FALSE, all models that are set to TRUE and that can be fitted will be
    reported.}
  \item{s0}{
    If the weibull model is fitted, s0 gives the possibility to adjust the
    starting value for the shape parameter of \code{\link{pweibull}}.}
  \item{b0,f0}{
    If the linearlogistic model is fitted, b0 and f0 give the possibility to
    adjust 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 \dQuote{inactive}. If the mean response at the lowest
    dose is smaller than 0.5, the modeltype is set to \dQuote{active}. In
    both cases, no fitting procedure is carried out.  Every successful fit is
    reported in one line. Parameters of the fitted curves are only reported
    if the fitted ED50 is not higher than the highest dose. 

    \code{ndl} is the number of dose levels in the raw data, \code{n} is the
    total number of data points in the raw data used for the fit
    \code{lld} is the decadic logarithm of the lowest dose and
    \code{lhd} is the decadic logarithm of the highest dose.  For the
    \dQuote{linlogit}, \dQuote{logit} and \dQuote{probit} models, the
    parameter \code{a} that is reported coincides with the logED50, i.e the
    logED50 is one of the model parameters that is being fitted, and
    therefore, depending on the argument \code{conf}, a standard deviation
    \code{std} or a confidence interval \code{conf} is reported for the
    logED50. In the case of the \dQuote{weibull} model, \code{a} is a
    location parameter.  Parameter \code{b} in the case of the
    \dQuote{linlogit} fit is the variable b from the \code{\link{linlogitf}}
    function. In the case of \dQuote{probit} fit it is the standard deviation
    of the fitted normal distribution, in the case of the \dQuote{logit} fit
    it is the \code{scale} parameter in the \code{\link{plogis}} function,
    and in the \dQuote{weibull} fit it is the \code{shape} parameter of the
    fitted \code{\link{pweibull}} function. Only the \dQuote{linlogit} fit
    produces a third parameter \code{c} which is the variable f from the
    \code{\link{linlogitf}} function.}
}
\examples{
data(antifoul)
r <- drfit(antifoul)
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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