Re: [R] GAM Chi-Square Difference Test

2012-07-16 Thread Simon Wood
Hi Will, Your edf interpretation is not quite right. The smooths are subject to a centring constraint for identifiability reasons, and this removes a degree of freedom, so EDF=1 corresponds to a straight line fit. On your second point and third points. anova(gamb1.1,gamb1.2, test="Chisq") co

[R] GAM Chi-Square Difference Test

2012-07-15 Thread wshadish
We are using GAM in mgcv (Wood), relatively new users, and wonder if anyone can advise us on a problem we are encountering as we analyze many short time series datasets. For each dataset, we have four models, each with intercept, predictor x (trend), z (treatment), and int (interaction between x an