[R] Regression trees with an ordinal response variable

[Stacey Buckelew]

Hi,

I am working on a regression tree in Rpart that uses a continuous response
variable that is ordered.  I read a previous response by Pfr. Ripley to a
inquiry regarding the ability of rpart to handle ordinal responses in
2003.  At that time rpart was unable to implement an algorithm to handle
ordinal responses.  Has there been any effort to rectify this in recent
years?

Thanks!

Stacey



On Mon, 2 Jun 2003, Andreas Christmann wrote:
> >>> 1. RE: Ordinal data - Regression Trees & Proportional Odds
> (Liaw, Andy)
>
> > AFAIK there's no implementation (or description) of tree algorithm
> > that handles ordinal response.
> >
>
> Regression trees with an ordinal response variable can be computed with
> SPSS Answer Tree 3.0.
They *can* be handled by tree or rpart in R.
I think Andy's point was that there is no consensus as to the right way to
handle them: certainly using the codes of categories works and may often
be reasonable, and treating ordinal responses as categorical is also very
often perfectly adequate.
Note that rpart is user-extensible, so it would be reasonably easy to write
an extension for a proportional-odds logistic regression model, if that is
thought appropriate (and it seems strange to me to impose such strong
structure on the model with such a general `linear predictor': POLR
models are often in my experience a poor reflection of real problems).
-- 
Brian D. Ripley,                  ripley at stats.ox.ac.uk
Professor of Applied Statistics,  http://www.stats.ox.ac.uk/~ripley/
University of Oxford,             Tel:  +44 1865 272861 (self)
1 South Parks Road,                     +44 1865 272860 (secr)
Oxford OX1 3TG, UK                Fax:  +44 1865 272595