Dear R Community, I am using the package DRC ( to fit a boltzman model to my data. I can fit the model and extract the lower limit, upper limit, and ED50 (aka V50), but I cannot figure out how to get the slope of the curve at ED50. Is there a simple way to do this? I've searched the mailing list and looked through the package documentation, but could not find anything. I am new to r, and especially the DRC package, so any help would be appreciated.
This gets me 3/4 of what I need: DATA: Dose,Response 0.85,0.0085 0.90,0.0096 0.95,0.0155 1.00,0.2725 1.05,0.3634 1.10,0.3508 1.15,0.5002 1.20,0.8826 1.25,0.7023 1.30,1.7934 1.35,0.7389 CODE: library( drc ) mydata <- read.csv( file="test.csv", header=T ) drc.preTBS <- drm( response ~ dose, data = mydata, fct= LL.4( names = c( "Slope", "Lower Limit", "Upper Limit", "ED50") ) ) For the data above, I would expect a slope at ED50 to be about 0.0714 (according to GraphPad). How can I determine the slope at ED50 for a Boltzmann fit using DRC or related packages? Thanks much! -Bob (Veterans Administration) ______________________________________________ R-help@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.