Okay. I did use example 6.12 to set up the analysis, but I got an error message that I need to specify type=random if I want to include random effects for the time-varying covariate. I had it specified as type=mixture. If I change it to type=random, then I get an error message that I have to use type=mixture if I want to specify a latent class variable. Any suggestions for what I can do differently?