Mechlorprop and terbythylazine tested on Lemna minor
Data consist of 5 mixture, 6 dilutions, three replicates, and 12 common controls; in total 102 onservations.
data(mecter)
A data frame with 102 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 asymmetric Voelund model is appropriate, whereas the symmetric Hewlett model is not.
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 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
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