Looking at that data, it looks like the two species respond differently to GDD. "Fitting a curve" means first defining and then fitting a model that, once fit, has fitted values that will give you the curve that you wold like to draw.
The simplest would be a series regression with interaction terms: weight_i = a + b1(gdd) + b2(species) + b3(gddxspecies) + b4(gdd^2) + b5(gdd^2 x species) .. more polynomials.. + e_i Better might be a "generalized additive model" where the continuous variables (both GDD and the GDD-species interaction) are replaced by smooth terms that are estimated nonparametricaly. The package here is 'mgcv', and the routine is 'gam'. The problems here are two: 1. GAMs are complicated stats. Learning how to do them right is an investment. 2. I don't think that the gam package yet gives functionality to put two smooth fits onto one plot, as you have. If you go this route and figure out how to plot more than one GAM fit on a plot, please let me know how you did it. -- View this message in context: http://r.789695.n4.nabble.com/Best-fitted-curve-tp4647692p4647703.html Sent from the R help mailing list archive at Nabble.com. ______________________________________________ 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.
