R: Mechlorprop and terbythylazine tested on Lemna minor

mecter {drc} | R Documentation

## 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

[Package drc version 3.0-1 Index]