R help - Jan 2011 - Circular variables within a GLM, GLM-GEE or GAM

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

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).

Simon

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