Hi,

I was hoping to get some advice on how to derive estimates of slopes from four parameter logistic models fit with SSfpl.

I fit the model using:

model<-nls(temp~SSfpl(time,a,b,c,d))
summary(model)

I am interested in the values of the lower and upper asymptotes (parameters a and b), but also in the gradient of the line at the inflection point (c) which I assume tells me my rate of increase when it is steepest (?).

However, I cannot work out how to derive a slope estimate. I'm guessing it has something to do with the scaling parameter d but having searched the internet for hours I have not made any progress, and it is probably quite simple. Any help would be hugely appreciated!

All the best

Sam

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