Dear Simone, you can use the package 'drc' to fit a logistic model, that is a non-linear regression model based on the equation c+(d-c)/(1+exp(b(x-e))), to your data (below named 'simone'):
## Fitting a 4-parameter logistic model (also called Boltzmann model) simone.m1 <- drm(size~x, data=simone, fct=B.4()) ## Plotting the data together with the fitted curve plot(simone.m1, log="") The fit is not great due to the bend. Christian ______________________________________________ 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.
