Glyphosate and metsulfuron-methyl tested on algae.
The dataset has 7 mixtures, 8 dilutions, two replicates and 5 common control controls. Four observations are missing, giving a total of 113 observations.
data(glymet)
A data frame with 113 observations on the following 3 variables.
dosea numeric vector of dose values
pcta numeric vector denoting the grouping according to the mixtures percentages
rgra numeric vector of response values (relative growth rates)
The dataset is analysed in Soerensen et al (2007). The concentration addition model can be entertained for this dataset.
The dataset is kindly provided by Nina Cedergreen, Department of Agricultural Sciences, Royal Veterinary and Agricultural University, Denmark.
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.
## 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
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