All factors (whether they're continuous or categorical) are included in the linear predictor.

See page 14 of Chapter 16, which says:

"X is the design matrix of factors" and also says that the linear predictor is:\[\eta =X\beta +\xi \]Notice that the Core Reading uses the word 'factor' as a generic term to cover both categorical and continuous variables (at the top of page 14 again). This illustrates Padasala's answer to your original question. (Thanks Padasala for your excellent response.)

Last edited: Jun 29, 2020