[S] plot.gam applied to glm object

Mark Grant (markg@uic.edu)
Thu, 10 Sep 1998 16:40:32 -0500

After fitting a logistic model with glm, I am using plot.gam to display
parameter results for a factored variable representing quintiles of body
mass index--"bmig". The first category is referent in the model (treatment
contrasts with the referent category having an odds ratio of 1--parameter
set to 0). However, plot.gam displays not the k-1 levels in the fitted
model but k levels (with apparently a constant added to each parameter
estimate); the y-axis is labeled as "partial for bmig".

Could someone explain 1) how the constant is obtained and 2) what is the
interpretation of "partial for bmig" displayed in the plot.

Mark Grant

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