[R-sig-eco] angular statistics

[Holland, Jeffrey D]

Hello Pete,
   You could include the sine and cosine of the angles.  A good book on this kind of analysis:
Fisher, N.I. 1993. Statistical Analysis of Circular Data. Cambridge Univ. Press.
To make this closer to exposure, perhaps you could first "rotate" the compass so that 360' is facing the direction of maximum exposure, and back-transform later?  Just a thought.
Cheers,  Jeff

____________________
Jeffrey D. Holland                                  (765) 494-7739
Assoc. Prof. of Landscape Ecology & Biodiversity    jdhollan #at# purdue.edu
Dept. of Entomology, Purdue University              Smith Hall B17, 901 W. State St., West Lafayette, IN 47907


-----Original Message-----
From: r-sig-ecology-bounces at r-project.org [mailto:r-sig-ecology-bounces at r-project.org] On Behalf Of Peter Nelson
Sent: Tuesday, October 15, 2013 1:00 PM
To: r-sig-ecology at r-project.org
Subject: [R-sig-eco] angular statistics

I want to include the exposure (measured in degrees, for example, East-facing is 90) of various coastal sites in GLM and CCA analyses. Is there an appropriate transformation that I can apply to these measurements that will allow me to do this? I've found plenty of information on comparing headings, calculating means, etc, but nothing on how exposure might be used as a continuous independent variable. 

Treating exposure as a categorical variable (East, Southwest, etc) seems like a fallback option, but then there is just as much of a 'difference' between SE and E sites as there is between SE and NW sites!

Thanks, Pete
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