For the general GAM in Equation 1, an additive dependence of the form
This implies that concurvity is highly dependent on the particular GAM being considered.
An exact concurvity relation causes the GAM to be unidentifiable (Ramsay et al.
Furthermore, the S-Plus gam function does not provide any diagnostic tests for assessing the presence of concurvity.
In theory, for any GAM in which the back-fitting algorithm converges, there exists a matrix R such that the fitted values [mu] are given by the relation [mu] = Rz, where z = g(y) is the vector of observations transformed by the link function.
The second stage employed a spatial GAM to relate mortality to air pollution by modeling the log-relative risks as the sum of a nonparametric function of location and a linear function of (average) airborne sulfate particle concentration.
2001) used the gam function in S-Plus to fit a smooth function f and a linear parameter [beta] = 0.