I'm fairly new to this site. I'm currently doing some research work that involves the use of non-linear mixed effect model on longitudinal data (R). I'm presently using Pinheiro and Bates' book, Mixed-Effects Models in S and S-PLUS, with the nlme package. By non-linear, I mean non-linear functions of independent variables with normal responses.
I'm still a beginner with statistics and I'm finding the theoretical treatment of the subject in the above book quite daunting to understand. I was wondering if there are other "easier to digest" resources (including books) out there to try and get to grips with the theory. I understand how to use it in R but I still find that there are some fundamental concepts and gaps in my knowledge.