drc (version 1.5-5)

acidiq: 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)

source

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

Details

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

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
acidiq.mfree <- drm(rgr~dose, pct, data=acidiq, fct = LL.4(),
pmodels = list(~factor(pct),~1,~1,~factor(pct) - 1), 
adjust = "bc1")

## Lack-of-fit test
anova(acidiq.mfree)
summary(acidiq.mfree)

## Plotting isobole structure
isobole(acidiq.mfree, exchange=0.1, xlim=c(0, 400), ylim=c(0,45))

## Fitting the concentration addition model
acidiq.mca <- mixture(rgr~dose, pct, data=acidiq, fct = LL.4(), 
collapse=~factor(pct), model="CA", boxcox=TRUE)

## Comparing to model with freely varying e parameter
anova(acidiq.mca, acidiq.mfree)  # rejected

## Plotting isobole based on concentration addition
isobole(acidiq.mfree, acidiq.mca, exchange=0.1, xlim=c(0, 420), ylim=c(0,45))  # poor fit

## Fitting the Hewlett model
acidiq.mhew <- mixture(rgr~dose, pct, data=acidiq, fct = LL.4(), 
collapse=~factor(pct), model="Hewlett", boxcox=TRUE)

## Comparing to model with freely varying e parameter
anova(acidiq.mfree, acidiq.mhew)  # accepted
summary(acidiq.mhew)

## Plotting isobole based on concentration addition
isobole(acidiq.mfree, acidiq.mhew, exchange=0.1, xlim=c(0, 400), ylim=c(0,45))  # good fit