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b12
2006 Nov 07
1
gamm(): nested tensor product smooths
...thers
y=f(x1)+f(x2) vs y=f(x1)+f(x2)+f(x1,x2)
(testing for additivity)
In mixed model representation, where X represents the unpenalized part of the spline functions and Z the "wiggly" parts, this would be:
y=X%*%beta+ Z_1%*%b_1+ Z_2%*%b_2
vs
y=X%*%beta+ Z_1%*%b_1+ Z_2%*%b_2 + Z_12 %*% b_12
where b are random effect vectors and the hypothesis to be tested is
H_0: Var(b_12)=0 (<=> b_12_i == 0 for all i)
the problem:
gamm() does not seem to support the use of nested tensor product splines,
does anybody know how to work around this?
example code: (you'll need to source the...