Mechlorprop and terbythylazine tested on Lemna minor

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

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

# NOT RUN {
library(drc)

## 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
# }