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

[Clare Embling]

Hi Simon,

Thanks for that!  Yes the circular variable is a predictor variable - great that it can be done using GAMs.
I actually would like to do a GAM-GEE model - do you know if I can do this within R yet?  I'm using GLM-GEEs because I can't do GAM-GEEs (I have data collected over the same survey route repeatedly over time, so want to take into account the fact that my data are not independent - I'm modelling my correlation structure using an ar-1 autoregressive correlation structure within a GEE). That way too, I can include my circular variables with circular smoothing functions as you suggested.

Best wishes & thanks,
Clare

________________________________________
From: Simon Wood [s.wood at bath.ac.uk]
Sent: 18 January 2011 17:58
To: r-help at r-project.org
Cc: Clare Embling
Subject: Re: [R] Circular variables within a GLM, GLM-GEE or GAM

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