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Today's Topics:
1. Warning with betareg (leanne heisler)
----------------------------------------------------------------------
Message: 1
Date: Tue, 30 Oct 2012 12:59:09 -0500
From: leanne heisler <leanneheis...@hotmail.com>
To: <r-sig-ecology@r-project.org>
Subject: [R-sig-eco] Warning with betareg
Message-ID: <col120-w73ff7f07d1f61c5a4dc17ae...@phx.gbl>
Content-Type: text/plain; charset="iso-8859-1"
Dear List,
I am looking for weather patterns affecting the composition of rodent communities. I have the proportions of species (DM,MV,SBV,OBPM,HM,NGM) and shrews (SHREW) from 2004 to 2011 and am using the betareg package and AIC model selection to identify which weather variables of the current year (PREC,GDD,SNOW) and/or previous year (PREC_T,, GDD_T,,SNOW_T)) are the best predictors of change in the relative abundance (% community) of each species.
I am not sure about the cause of the error....but you shouldn't do a
regression type analysis with so few observations. General
recommendation is to have 15-25 observations per covariate. Eight
observations doesn't bring you that far. And certainly not 3 covariates
with 8 observations!
Alain
ab
X DM MV SBV SHREW OBPM HM NGM PREC GDD
SNOW PREC_T1 GDD_T1 SNOW_T1
1 2004 0.2583 0.1301 0.5685 0.0215 0.00291 0.00101 0.01761 301.53 1572.14 4.67
258.06 1747.26 10.00
2 2005 0.2539 0.1258 0.5448 0.0478 0.00541 0.00461 0.01771 373.70 1564.48 18.33
301.53 1572.14 4.67
3 2006 0.3595 0.1131 0.4088 0.0474 0.02551 0.01091 0.03471 235.60 1884.40 11.33
373.70 1564.48 18.33
4 2007 0.4839 0.3441 0.0968 0.0753 0.00001 0.00001 0.00001 290.44 1753.85 34.00
235.60 1884.40 11.33
5 2008 0.4632 0.2436 0.2309 0.0326 0.00001 0.00851 0.02121 294.70 1631.28 23.00
290.44 1753.85 34.00
6 2009 0.2600 0.3102 0.3744 0.0482 0.00211 0.00051 0.00471 257.45 1697.45 38.67
294.70 1631.28 23.00
7 2010 0.7219 0.0888 0.0947 0.0592 0.00001 0.00591 0.02961 386.45 1459.83 33.00
257.45 1697.45 38.67
8 2011 0.3204 0.4611 0.1222 0.0463 0.04811 0.00191 0.00001 214.30 1662.87 72.00
386.45 1459.83 33.00
I have successfully modeled all species up to OBPM, but have run into a warning
message that I haven't been able to decipher (below).
library(betareg)
betareg <- betareg(OBPM ~ GDD_T,, data=ab)
Error in while (testhalf & stepFactor < ))) { :
missing value where TRUE/FALSE needed
In addition: Warning message:
In sqrt(wpp) : NaNs produced
I'm sure this is something simple, but if anyone could help me with this it
would be greatly appreciated.
Thank you in advance,
---------------
Leanne Heisler
Graduate Student
Department of Biology
University of Regina
Canada
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End of R-sig-ecology Digest, Vol 55, Issue 12
*********************************************
--
Dr. Alain F. Zuur
First author of:
1. Analysing Ecological Data (2007).
Zuur, AF, Ieno, EN and Smith, GM. Springer. 680 p.
URL: www.springer.com/0-387-45967-7
2. Mixed effects models and extensions in ecology with R. (2009).
Zuur, AF, Ieno, EN, Walker, N, Saveliev, AA, and Smith, GM. Springer.
http://www.springer.com/life+sci/ecology/book/978-0-387-87457-9
3. A Beginner's Guide to R (2009).
Zuur, AF, Ieno, EN, Meesters, EHWG. Springer
http://www.springer.com/statistics/computational/book/978-0-387-93836-3
4. Zero Inflated Models and Generalized Linear Mixed Models with R. (2012)
Zuur, Saveliev, Ieno.
http://www.highstat.com/book4.htm
Other books: http://www.highstat.com/books.htm
Statistical consultancy, courses, data analysis and software
Highland Statistics Ltd.
6 Laverock road
UK - AB41 6FN Newburgh
Tel: 0044 1358 788177
Email: highs...@highstat.com
URL: www.highstat.com
URL: www.brodgar.com
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