R-helpers,
I recently submitted a help request for the predict.drm function found in the
drc package. I am still having issues with the function and I am submitting
reproducible code hoping that somebody can help me figure out what is going on.
--------
library(drc)
# Fit a 4 parameter logistic model to ryegrass dataset
fit <- drm(rootl ~ conc, data = ryegrass, fct = LL.4())
summary(fit)
# Generate a fake dataset for prediction
newdt <- data.frame( matrix(c(seq(0.2, 9, 0.01), rep(NA,881)), ncol=2))
colnames(newdt) <- c('rootl', 'conc')
# Generate prediction intervals and confidence intervals
prd.p <- predict(fit, newdata=newdt, interval='prediction')
prd.c <- predict(fit, newdata=newdt, interval='confidence')
# Check output
> head(prd.p)
Prediction Lower Upper
[1,] 7.790812 NA NA
[2,] 7.790476 NA NA
[3,] 7.790106 NA NA
[4,] 7.789702 NA NA
[5,] 7.789262 NA NA
[6,] 7.788784 NA NA
> head(prd.c)
Prediction Lower Upper
[1,] 7.790812 NA NA
[2,] 7.790476 NA NA
[3,] 7.790106 NA NA
[4,] 7.789702 NA NA
[5,] 7.789262 NA NA
[6,] 7.788784 NA NA
--------
There appears to be a problem with the predict.drc function. This code
previous generated confidence and prediction intervals in columns 2 and 3 of
the prediction matrices but now fails for reasons unknown to me. Anyone have
an idea of what is going on and how I can remedy the situation?
Brant Inman
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