hi all,

First, thank you all for your replies to my question about modeling
non-linear trends in abundance for declining populations.  I am a newcomer
to this list, but I will now follow it actively.  In response to your
suggestions, I have spent the day playing with various tools, from time
series to 'multivariate additive regression splines.'  I have learned a lot,
and narrowed in on what exactly it is that I want for my data.

Most of the analyses I am doing are about ecological correlates of
extirpation -- which I have not mentioned here because I already know what
to do.  When it comes to the population trends over time, I have found that
the best tool seems to be a fit derived from a general additive model (I am
using the "gam" package, though I know there are others out there; I don't
know which is best).  Which leaves me with one follow-up question that I'm
hoping someone can help with....

If I fit a general additive model using the gam package (or tell me to use a
different package), is there a way that I can extract or identify the
largest knot, in terms of the predictor variable.  All I want (modest
desire, I hope) is to drop a vertical line to the x-axis at the largest kink
in the line, which will visualize the year that a population started to go
down.  I can draw a line in R, the question is how to pull out the number
that is the kink.

(A follow-follow-up question might be... is there a way to say that some
kinks are more significant than others? )

thanks!
Matt


-- 
Matthew L Forister
Assistant Professor
Department of Biology / MS 314
1664 N. Virginia St.
University of Nevada, Reno
Reno, Nevada 89557
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E-mail: forister@gmail.com
Office phone: (775) 784 - 6770
Lab phone: (775) 784 - 7083
Fax: (775) 784 - 1302
Office: room 257 Fleischmann Agriculture Building
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Webpage:
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