[R] Circular variables within a GLM, GLM-GEE or GAM

Simon Wood s.wood at bath.ac.uk
Tue Jan 18 18:58:27 CET 2011

Is the variable to be used as a predictor? If so mgcv::gam has a couple of 
circular smoother built in... 

s(x,bs="cc") or s(x,bs="cp") 

(if the range of x is less than the full  [0, 360] then you can supply a 
`knots' argument to gam to force the x range to go from 0 to 360, otherwise  
s(min(x), bs="c*") will be identical to s(max(x),bs="c*"), which may not be 
matching in the right place).


On Tuesday 18 January 2011 12:07, Clare Embling wrote:
> Hi,
> I have a variable (current speed direction) which is circular (0=360
> degrees), and I'd like my GLM to include the variable as a circular
> variable.  Can I do this?  And what is the code?
> I'm actually doing a GLM-GEE using the 'geepack' package, so want to use it
> in that, but also interested in whether it can also be used in GLMs and
> GAMs (I use the 'mgcv' package for GAMs).
> Any help would be gratefully received,
> Thanks in advance,
> :o) Clare
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> Simon Wood, Mathematical Sciences, University of Bath, Bath, BA2 7AY UK
> +44 1225 386603  www.maths.bath.ac.uk/~sw283

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