Re: [R] nlme problems

From: Spencer Graves <>
Date: Tue 20 Dec 2005 - 03:42:47 EST

          Are you familiar with Pinheiro and Bates (2000) Mixed-Effects Models in S and S-Plus (Springer)? I suspect that book, especially the latter half, might contain the information you seek.

          spencer graves
p.s. PLEASE do read the posting guide! "". Anecdotal evidence suggests that posts more consistent with that guide tend to receive quicker, more useful replies.

Ken Beath wrote:

> I meant fitting not maximising, it is a nonlinear mixed effects
> model, with both fixed and random effects. My assumption is that for
> the function I am using the approximation approach used in nlme is
> not quite close enough, and nothing much that I can do, except for
> looking at starting values. I was hoping that someone would have
> other suggestions, so I will keep attempting to understand the
> control parameters. I can add an extra parameter to the model and
> obtain a worse fit.
> Ken
> Dieter Menne writes:

>>>I'm maximising a reasonably complex function using nlme (version
>>>3.1-65, have also tried 3.1-66) and am having trouble with fixed
>>>parameter estimates slightly away from the maximum of the log
>>>likelihood. I have profiled the log likelihood and it is a parabola
>>>but with sum dips. Interestingly changing the parameterisation moves
>>>the dips around slightly. Unfortunately the PNLS step is finding a
>>>maximum at the dips rather than the mle. I have tried using starting
>>>values for the fixed parameters without change. Any ideas ?
>>you should not use nlme for "maximising a complex function",  
>>because it's a
>>rather specialized tool for mixed-model statistical analysis. Try  
>>to use optim
>>directly, which has quite a few methods to choose from, and one of  
>>them might
>>work for your problem.

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Spencer Graves, PhD
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Received on Tue Dec 20 03:50:54 2005

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