Hello S-Newsers,
I've read through Pinheiro and Bates, searched the help files and s-news
archives, and even googled, all to no avail (this question has come up on
s-news, just no answers posted).
I think (and please correct me if I'm wrong!), I need to create a new
corStruct class. Does anyone have a primer (or advice) on how to define a
new corStruct class by specifying a constructor function, and methods for
the functions corMatrix and coef? Details of what I'm trying to do are
below...
It feels like what I'm wanting to do is straight-forward (which is
probably my first mistake). Samples were taken from four lakes, each
lake was visited on multiple days (between 8-12 days per year for 3
years during the summer), and on each visit, 3 samples were taken.
I want account for the correlation between samples taken on the same day
from a given lake and the correlation between samples taken from different
days of that lake.
I could easily do this with a symmetric correlation structure using Lake
as the only level (e.g., corSymm(~1|Lake)) and let the model sort out the
details. I'd rather test to see if a simpler structure would be as good
(e.g., within-day observations being compound symmetric and between day
observations of the same lake be either compound symmetric, symmetric, or
AR1). The corStrat() function will allow me estimate different
correlation structures (or values) within a hierarchy (e.g. each lake
having a different correlation), but that's not really what I want, yet.
Any thoughts would be greatly appreciated! I will post a summary of
replies to the list.
Thank you for your help!
Cheers,
Andy
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"What if the Hokey Pokey is all it really is about?" - Jimmy Buffett
Andrew B. Cooper, Ph.D.
Department of Natural Resources
Institute for the Study of Earth, Oceans and Space
Morse Hall 142
University of New Hampshire
Durham, NH 03824
andrew.cooper@unh.edu
603.862.4254, 603.862.0243 (FAX)
http://www.unh.edu/natural-resources/fac-cooper.html
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