R: Glyphosate and metsulfuron-methyl tested on algae.

glymet {drc} | R Documentation

## Glyphosate and metsulfuron-methyl tested on algae.

### Description

The dataset has 7 mixtures, 8 dilutions, two replicates and 5 common control controls. Four observations are missing, giving a total of 113 observations.

### Usage

    data(glymet)

### Format

A data frame with 113 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 concentration addition model can be entertained 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
    glymet.free <- drm(rgr~dose, pct, data = glymet,
    fct = LL.3(), pmodels = list(~factor(pct) , ~1, ~factor(pct)))

    ## Lack-of-fit test
    modelFit(glymet.free)  # acceptable
    summary(glymet.free)

    ## Plotting isobole structure
    isobole(glymet.free, exchange=0.01)

    ## Fitting the concentration addition model
    glymet.ca <- mixture(glymet.free, model = "CA")

    ## Comparing to model with freely varying e parameter
    anova(glymet.ca, glymet.free)  # borderline accepted

    ## Plotting isobole based on concentration addition
    isobole(glymet.free, glymet.ca, exchange = 0.01)  # acceptable fit

    ## Fitting the Hewlett model
    glymet.hew <- mixture(glymet.free, model = "Hewlett")

    ### Comparing to model with freely varying e parameter
    anova(glymet.ca, glymet.hew)
    # borderline accepted
    # the Hewlett model offers no improvement over concentration addition

    ## Plotting isobole based on the Hewlett model
    isobole(glymet.free, glymet.hew, exchange = 0.01)
    # no improvement over concentration addition

[Package drc version 3.0-1 Index]