Great, thanks for your reply!

I've just tracked down a copy of Pinheiro & Bates (2000) so I'll look at
that, too.

Thanks again, Mark


On Fri, Aug 22, 2008 at 9:56 AM, Christoph Scherber <
Christoph.Scherber@agr.uni-goettingen.de> wrote:

> Dear Mark,
>
> I would include the repeated measure as the smallest stratum in the random
> effects specification:
>
> random=~1|sampleunit/year
>
> Setting up user-defined variance structures should be possible using for
> example:
>
> weights=varPower(form=~habitat)
>
> or also try out the available corStruct() classes (found in Pinheiro and
> Bates 2000)
>
> HTH
> Christoph
>
>
>
>
> Mark Na schrieb:
>
>> Hello,
>>
>> We are attempting to use nlme to fit a linear mixed model to explain bird
>> abundance as a function of habitat:
>>
>>
>> lme(abundance~habitat-1,data=data,method="ML",random=~1|sampleunit)
>>
>> The data consist of repeated counts of birds in sample units across
>> multiple
>> years, and we have two questions:
>>
>> 1) Is it necessary (and, if so, how) to specify the repeated measure
>> (years)? As written, the above code does not.
>>
>> 2) How can we specify a Toeplitz heterogeneous covariance structure for
>> this
>> model? We have searched the help file for lme, and the R-help archives,
>> but
>> cannot find any pertinent information. If that's not possible, can we
>> adapt
>> an existing covariance structure, and if so how?
>>
>> Thanks, Mark
>>
>>        [[alternative HTML version deleted]]
>>
>> ______________________________________________
>> R-help@r-project.org mailing list
>> https://stat.ethz.ch/mailman/listinfo/r-help
>> PLEASE do read the posting guide
>> http://www.R-project.org/posting-guide.html
>> and provide commented, minimal, self-contained, reproducible code.
>>
>> .
>>
>>
> --
> Dr. rer.nat. Christoph Scherber
> University of Goettingen
> DNPW, Agroecology
> Waldweg 26
> D-37073 Goettingen
> Germany
>
> phone +49 (0)551 39 8807
> fax   +49 (0)551 39 8806
>
> Homepage http://www.gwdg.de/~cscherb1 <http://www.gwdg.de/%7Ecscherb1>
>

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