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.
A data frame with 180 observations on the following 3 variables.
a numeric vector of dose values
a numeric vector denoting the grouping according to the mixtures percentages
a numeric vector of response values (relative growth rates)
The dataset is analysed in Soerensen et al (2007). Hewlett's symmetric model seems appropriate 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 ## 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