Hi Bill, have a look at the following artificial example:
## Loading the package 'drc' (on CRAN) library(drc) ## Generating dataset with four dose-response curves finneyx4 <- rbind(finney71, finney71, finney71, finney71) ## Generating artificial points (x,y) ## different pairs for each of the 4 curves in the above dataset finneyx4$x <- rep(1, 24) finneyx4$y <- rep(1:4, c(6, 6, 6, 6)) ## Fitting the two-parameter log-logistic model (logistic regression) m1 <- drm(affected/total ~ dose, as.factor(x):as.factor(y), weights = total, data = finneyx4, fct = LL.2(), type = "binomial") ## Calculating ED50/LD50 for each location (they are all the same for this dataset) ED(m1, 50) You could try the same approach for your data! Christian ______________________________________________ [email protected] 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.
