+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.