[R-sig-ME] Modeling polar coordinates

[David Duffy]

On Tue, 24 Aug 2010, Titus von der Malsburg wrote:

> Your [Luca's] suggestion about using sin and cos combinations sounds
> interesting, but your description is a bit too terse for me.
>
>  mer.cos <- lmer(cos(x) ~ 1 + factor + (1|subject), my.data.frame)
>  mer.sin <- lmer(sin(x) ~ 1 + factor + (1|subject), my.data.frame)
>
> This is of course modulo some transformation that makes the residuals
> being normally distributed.  (Which would that be?)

I can't see it being that simple. AFAICT (Song, Correlated Data Analysis), 
the Fisher and Lee model uses a tan(z/2) link function for the mean, *and* 
1/2 sec^2(z/2) for the dispersion.  You might be able to directly maximize 
the wrapped normal likelihood (from the circular package) for your model.

Just 2c, David Duffy.

-- 
| David Duffy (MBBS PhD)                                         ,-_|\
| email: davidD at qimr.edu.au  ph: INT+61+7+3362-0217 fax: -0101  /     *
| Epidemiology Unit, Queensland Institute of Medical Research   \_,-._/
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