[R-sig-dyn-mod] Venezuelan census models

Thomas Petzoldt Thomas.Petzoldt at TU-Dresden.de
Sat Jan 5 13:26:29 CET 2013


Hello,

just a few thoughts:

1) Consideration of growth directly instead of (or in addition to) 
population abundance seems to be a good idea. Thanks for this idea.

2) I agree with Hans, that the purpose of the model counts, i.e. 
description of data, statistical testing, mechanistic systems 
understanding or prediction.

3) For a statistical model comparison, the sum of squares alone is not 
enough and model complexity (number of parameters) needs to be taken 
into account.

Re-fitting the two-compartment models with 3 resp. 5 parameters with 
nlsLM from package minpack.lm, we get:


 > AIC(res3, res5)
      df      AIC
res3  4 385.5084
res5  6 384.0203

We see that res5, the model with 5 parameters performs (indeed and only) 
a little bit better.

However, validity of all the autonomous models applied so far is rather 
limited and estimated saturation levels remain pure speculation. 
Therefore, non-autonomous models are required that consider external 
(i.e. "environmental") factors.

Thomas P.


PS: Code can be provided in case of interest.



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