[R] repeated measure test

Bert Gunter gunter.berton at gene.com
Fri Nov 12 16:27:03 CET 2010


Obviously, you would do better to consult a local statistician.
Presumably, you have none, so you would probably do better posting on
appropriate R SIGs -- e.g. R-sig-mixed-models, R-sig-ecology and the
liike. R-help is really not designed for this (although good souls
sometimes respond). In a similar vein, you might try seacrhing the net
for non-R statistical lists that might be helpful.

-- Bert

On Fri, Nov 12, 2010 at 5:40 AM,  <Steve_Friedman at nps.gov> wrote:
> Hi,
> This is a question regarding technique rather than an R specific issue.  I
> have been asked to evaluate a 30+ year long term continuous survey of bird
> presence/absence data that has an associated ocular estimate of the
> vegetation community percent coverage.  The data are organized by
> subpopulations (5), and by year ( 1991 - present).  We are interested in
> gaining understanding on whether bird presence is 1) related to vegetation
> community cover and 2) whether that relationship is variable over the
> period of record.  Ultimately I can associate management to this, but that
> data has not be pulled together yet for this survey.
> My first thought was to simply look to a clustering and nmds to examine
> which sites were more similar given the vegetation community.    Following
> this I had intended to repeat that analysis using year as a grouping
> variable to see if the clusters change.   This would then provide the basis
> for a trajectory analysis.
> Ok, so that might be rather very simple, I'm now considering a repeated
> measures approach, but do not have much experience here.  Since every site
> is the same in all years, what changes is the bird count and perhaps the
> vegetation community coverage estimates.
> Can someone let me know if this alternate approach is a better approach and
> how to conduct the analysis in R?
> Thanks very much.  If additional information is needed I can provide it,
> but I didn't want to fill mail boxes with unnecessary info at this time.
> Steve
> Steve Friedman Ph. D.
> Spatial Statistical Analyst
> Everglades and Dry Tortugas National Park
> 950 N Krome Ave (3rd Floor)
> Homestead, Florida 33034
> Steve_Friedman at nps.gov
> Office (305) 224 - 4282
> Fax     (305) 224 - 4147
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> and provide commented, minimal, self-contained, reproducible code.

Bert Gunter
Genentech Nonclinical Biostatistics

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