## Mechlorprop and terbythylazine tested on Lemna minor

### Description

Data consist of 5 mixture, 6 dilutions, three replicates, and 12 common controls; in total 102 onservations.

### Usage

data(mecter)

### Format

A data frame with 102 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).
The asymmetric Voelund model is appropriate, whereas the symmetric Hewlett model is not.

### 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
mecter.free <- drm(rgr ~ dose, pct, data = mecter,
fct = LL.4(), pmodels = list(~1, ~1, ~1, ~factor(pct) - 1))
## Lack-of-fit test
modelFit(mecter.free) # not really acceptable
summary(mecter.free)
## Plotting isobole structure
isobole(mecter.free, exchange = 0.02)
## Fitting the concentration addition model
mecter.ca <- mixture(mecter.free, model = "CA")
## Comparing to model with freely varying e parameter
anova(mecter.ca, mecter.free) # rejected
## Plotting isobole based on concentration addition
isobole(mecter.free, mecter.ca, exchange = 0.02) # poor fit
## Fitting the Hewlett model
mecter.hew <- mixture(mecter.free, model = "Hewlett")
## Comparing to model with freely varying e parameter
anova(mecter.hew, mecter.free) # rejected
## Plotting isobole based on the Hewlett model
isobole(mecter.free, mecter.hew, exchange = 0.02) # poor fit
## Fitting the Voelund model
mecter.voe<-mixture(mecter.free, model = "Voelund")
## Comparing to model with freely varying e parameter
anova(mecter.voe, mecter.free) # accepted
## Plotting isobole based on the Voelund model
isobole(mecter.free, mecter.voe, exchange = 0.02) # good fit