Submodel selection using dredge and gam (mgcv)
Hi Arnaud,
your question has in fact nothing to do with gam or model selection.
What you are asking is: what is the logical expression that yields True
when AB is False or both A and B are True. Now replace the words with
operators (!AB | (A & B)) and voil?.
See also:
help("Logic", "base")
fortunes::fortune(350)
best,
kamil
On 2014-11-10 21:26, Arnaud Mosnier wrote:
Hi, I want to use dredge to test several gam submodels including interactions. I tried to find a way in order to keep models with interaction only if the single variables occurring in the interaction are also included. i.e.: for y~s(x0)+s(x1)+ti(x0, x1) I want to keep y ~ s(x0) y ~ s(x1) y ~ s(x0) + s(x1) y ~ s(x0) + s(x1) + ti(x0,x1) and I want to remove y ~ s(x0) + ti(x0,x1) y ~ s(x1) + ti(x0,x1) y ~ ti(x0,x1) I know that I should use the "subset" option of the dredge function. However, I can not find the correct matrix / expression to obtain what I need ! Here a small example. ################ # Create some data (use mgcv example) library(mgcv) set.seed(2) dat <- gamSim(1,n=400,dist="normal",scale=2) # Create the global gam model # Here a model with interaction. Note the use of ti() bt <- gam(y~s(x0)+s(x1)+s(x2)+s(x3)+ti(x1,x2), data=dat,method="ML") # Use dredge to test sub-models library(MuMIn) print(modstab <- dredge(bt)) # Here the 11th model include the interaction but do not include the single variables x1 and x2 # ... I want to avoid that kind of model. get.models(modstab, subset = 11) ################ Any help would be appreciated ! Arnaud