Dear List I am trying to use gam function in mgcv 17.26. I have a big data set of about 40,000 data points. Every time that I run it ,it results in GCV score of "0" Family: gaussian Link function: identity Formula: D ~ s(Ghazl_res) + s(Depth) Estimated degrees of freedom: 3.77 2.91 total = 7.68 GCV score: 0 Plotting the curves of the predictor variables also gives a straight horizontal line along the zero value of the y axis. I really couldn't interpret whats going wrong. Appreciate it if anyone can comment Husam El Alqamy, B.Sc, M.Phil. Sr. Biodiversity GIS Analyst, Enivronmental Information Sector Environment Agency - Abu Dhabi [[alternative HTML version deleted]]