## Acifluorfen and diquat tested on Lemna minor.

### Description

Data from an experiment where the chemicals acifluorfen and diquat tested on Lemna minor. The dataset has 7 mixtures used in
8 dilutions with three replicates and 12 common controls, in total 180 observations.

### Usage

data(acidiq)

### Format

A data frame with 180 observations on the following 3 variables.

`dose`

a numeric vector of dose values

`pct`

a numeric vector denoting the grouping according to the mixtures percentages

`rgr`

a numeric vector of response values (relative growth rates)

### Details

The dataset is analysed in Soerensen et al (2007).
Hewlett's symmetric model seems appropriate for this dataset.

### Source

The dataset is kindly provided by Nina Cedergreen, Department of Agricultural Sciences,
Royal Veterinary and Agricultural University, Denmark.

### References

Soerensen, H. and Cedergreen, N. and Skovgaard, I. M. and Streibig, J. C. (2007)
An isobole-based statistical model and test for synergism/antagonism in binary mixture toxicity experiments,
*Environmental and Ecological Statistics*, **14**, 383–397.

### Examples

## Fitting the model with freely varying ED50 values
## Ooops: Box-Cox transformation is needed
acidiq.free <- drm(rgr ~ dose, pct, data = acidiq, fct = LL.4(),
pmodels = list(~factor(pct), ~1, ~1, ~factor(pct) - 1))
## Lack-of-fit test
modelFit(acidiq.free)
summary(acidiq.free)
## Plotting isobole structure
isobole(acidiq.free, xlim = c(0, 400), ylim = c(0, 450))
## Fitting the concentration addition model
acidiq.ca <- mixture(acidiq.free, model = "CA")
## Comparing to model with freely varying e parameter
anova(acidiq.ca, acidiq.free) # rejected
## Plotting isobole based on concentration addition -- poor fit
isobole(acidiq.free, acidiq.ca, xlim = c(0, 420), ylim = c(0, 450)) # poor fit
## Fitting the Hewlett model
acidiq.hew <- mixture(acidiq.free, model = "Hewlett")
## Comparing to model with freely varying e parameter
anova(acidiq.free, acidiq.hew) # accepted
summary(acidiq.hew)
## Plotting isobole based on the Hewlett model
isobole(acidiq.free, acidiq.hew, xlim = c(0, 400), ylim = c(0, 450)) # good fit