Results: Computation times

ADMBRE: 0.58 seconds.
nlme: 1.6 seconds under SPlus 6.1.



Model description
A growth curve model was fitted to the "orange tree" data by Pinheiro & Bates (2000, Ch.8.2)
as an illustration of the R (SPlus) routine nlme.
The logistic growth curve is given as
y = f_{1}
/(1 + exp[(tf_{2})/f_{3}])
] + e,
where y is the response and t is the age of the three.
The regression parameters to be estimated are: f_{1}, f_{2}
and f_{3}, and e is the residual error term. A random effect u is added to the parameter
f_{1}. A full description of the model can be found here:
orange.pdf.
Comparison with nlme
Parameter estimates are shown in the following table.

f_{1} 
f_{2} 
f_{3} 
SD(e) 
SD(u) 
ADMBRE 
192.1 
727.9 
348.1 
7.843 
31.65 
Std. dev. 
15.658 
35.249 
27.08 
1.013 
10.26 
nlme 
191.0 
722.6 
344.2 
7.846 
31.48 
The difference between the estimates obtained with ADMBRE and nlme
is small. The difference is caused by the fact that the two approaches 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).
