R: Acifluorfen and diquat tested on Lemna minor.

acidiq {drc} | R Documentation

## 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

[Package drc version 3.0-1 Index]