A model from pharmacokinetics;  

Model descriptionPinheiro & Bates (2000, Ch. 6.4) fitted a socalled 'onecompartment open model' to a dataset known as the 'phenopharbital data'. A patient is given a dose D at time t_{d}, giving rise to a phenopharbital concentration c_{t} at a later time t:c_{t} = D/V
exp[Cl/V(tt_{d})], where V and Cl are parameters (the socalled 'Volume of concentration' and the 'Clearance', respectively). Doses given at different time points contribute additively to c_{t}. Pinheiro & Bates (2000) fitted a model with a linear predictor (and a loglink) for each of the paramere V and Cl. Each of the linear predictors contained one covariate Wt and one random effect. A full description of the model can be found here: pheno.pdf ResultsThe results produced by ADMBRE and nlme are rather similar. The small difference is caused by the fact that the two methods use different approximations to the likelihood function. (ADMBRE uses the Laplace approximation, and for nlme the reader is referred to ( Pinheiro & Bates, 2000, Ch. 7).) 