R help - Feb 2011 - unequally spaced factor levels orthogonal polynomial contrasts coefficients trend analysis

Hello [R]-help

I am trying to find
> a package where you can do ANOVA based trend analysis on grouped data
> using orthogonal polynomial contrasts coefficients, for unequally
> spaced factor levels. The closest hit I've had is from this web site:
>(http://webcache.googleusercontent.com/search?q=cache:xN4K_KGuYGcJ:www.datavis.ca/sasmac/orpoly.html+Orthogonal+polynomial
>l
but I cannot find this package or anything like it.


      
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polynomial contrasts with the scores argument should do what you want.

?contr.poly

As an example:


contr.poly(4, c(1,2,4,8))
diff(contr.poly(4, c(1,2,4,8))[,1])



On Wed, Feb 2, 2011 at 2:40 PM, Asan Ramzan <asanramzan@yahoo.com> wrote:
> Hello [R]-help
>
> I am trying to find
> > a package where you can do ANOVA based trend analysis on grouped data
> > using orthogonal polynomial contrasts coefficients, for unequally
> > spaced factor levels. The closest hit I've had is from this web
site:
> >(
>
http://webcache.googleusercontent.com/search?q=cache:xN4K_KGuYGcJ:www.datavis.ca/sasmac/orpoly.html+Orthogonal+polynomial
> >l
>
> but I cannot find this package or anything like it.
>
>
>
>        [[alternative HTML version deleted]]
>
> ______________________________________________
> R-help@r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide
>
http://www.R-project.org/posting-guide.html<http://www.r-project.org/posting-guide.html>
> and provide commented, minimal, self-contained, reproducible code.
>
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If you know the spacing between the factor levels, then why not just treat it as
a numeric vector and use the poly function to create orthogonal polynomials of
the numeric variable.

If you have an unequally spaced ordered factor that does not lend itself to the
above, then I don't see that any type of polynomial contrasts makes sense
and would use something else that does (comparing neighboring pairs maybe).

-- 
Gregory (Greg) L. Snow Ph.D.
Statistical Data Center
Intermountain Healthcare
greg.snow at imail.org
801.408.8111

> -----Original Message-----
> From: r-help-bounces at r-project.org [mailto:r-help-bounces at r-
> project.org] On Behalf Of Asan Ramzan
> Sent: Wednesday, February 02, 2011 12:41 PM
> To: r-help at r-project.org
> Subject: [R] unequally spaced factor levels orthogonal polynomial
> contrasts coefficients trend analysis
> 
> Hello [R]-help
> 
> I am trying to find
> > a package where you can do ANOVA based trend analysis on grouped data
> > using orthogonal polynomial contrasts coefficients, for unequally
> > spaced factor levels. The closest hit I've had is from this web
site:
> >(http://webcache.googleusercontent.com/search?q=cache:xN4K_KGuYGcJ:www
> .datavis.ca/sasmac/orpoly.html+Orthogonal+polynomial
> >l
> 
> but I cannot find this package or anything like it.
> 
> 
> 
> 	[[alternative HTML version deleted]]
> 
> ______________________________________________
> R-help at r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide http://www.R-project.org/posting-
> guide.html
> and provide commented, minimal, self-contained, reproducible code.