Dear List,
The formula expression in a glmm call is typically linear, which I
believe is a requirement in order to preserve the assumption of odds
proportionality. Is glmm capable of fitting a non-linear function of a
covariate? In medical research a popular nonlinear function is the Emax
model. For instance dose effect could be linear up to a point but would
plateau at higher levels. Although a polynomial in dose may be a good
compromise, but occasionally results are unsatisfactory. Use of Emax
models in a glmm problem has been successfully dealt with using the
package NONMEM and recently WinBugs and SAS. I am curious if the
non-linearity poses a theoretical challenge, a computational one or
both?
Thanks
Farkad Ezzet Ph. D.
Pharsight Corporation
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