There is precedent in the ecological literature for using a cosine transformation IF you have reason to believe that your predictor varies continuously and symmetrically in its effects around a circle. For example, if due east were the "most" exposure, and due west the least, with due north and south being roughly equal, you could create a new predictor called "east.exposure" with (most basically)
east.exposure = cos(exposure - PI/2) Many more complicated extensions of this idea are possible, associated with nonlinear or asymmetrical gradients, but I will leave that to you or others on the list. On Oct 15, 2013, at 9:59 AM, Peter Nelson wrote: > 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 > _______________________________________________ > R-sig-ecology mailing list > R-sig-ecology@r-project.org > https://stat.ethz.ch/mailman/listinfo/r-sig-ecology Don McKenzie Affiliate Professor School of Environmental and Forest Sciences University of Washington d...@uw.edu [[alternative HTML version deleted]] _______________________________________________ R-sig-ecology mailing list R-sig-ecology@r-project.org https://stat.ethz.ch/mailman/listinfo/r-sig-ecology
