[R] Regression trees with an ordinal response variable

[Torsten Hothorn]

On Fri, 2 Feb 2007, Henric Nilsson (Public) wrote:

> Den Fr, 2007-02-02, 06:03 skrev 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?
>
> The `ctree' function in the `party' package is able to handle ordered
> responses, but note that there are fundamental differences between the
> former and `rpart'. Reading the package vignette and the relevant
> references will help.
>

Hi Henric,

> However, at the moment there seems to be a problem related to the ordinal
> case (predicted probabilities > 1) and I've CC:ed the package's maintainer
> (Torsten Hothorn).
>

yep, you are right (as always)-- a bug introduced by a fix, grrr. Its a 
little bit more complicated, but I'll make correct predictions available 
again *asap*.

Thanks!

Torsten

>
> HTH,
> Henric
>
> - - - - -
>
> Torsten, consider the following:
>
>> ### ordinal regression
>> mammoct <- ctree(ME ~ ., data = mammoexp)
> Warning message:
> no admissible split found
>> ### estimated class probabilities
>> treeresponse(mammoct, newdata = mammoexp[1:5, ])
> [[1]]
> [1] 1.822115
>
> [[2]]
> [1] 1.265487
>
> [[3]]
> [1] 1.822115
>
> [[4]]
> [1] 1.560440
>
> [[5]]
> [1] 1.822115
>
>> sessionInfo()
> R version 2.4.1 Patched (2007-01-06 r40399)
> i386-pc-mingw32
>
> locale:
> LC_COLLATE=Swedish_Sweden.1252;LC_CTYPE=Swedish_Sweden.1252;LC_MONETARY=Swedish_Sweden.1252;LC_NUMERIC=C;LC_TIME=Swedish_Sweden.1252
>
> attached base packages:
> [1] "stats4"    "grid"      "splines"   "stats"     "graphics"  "grDevices"
> [7] "utils"     "datasets"  "methods"   "base"
>
> other attached packages:
>      party         vcd  colorspace        MASS strucchange    sandwich
>    "0.9-8"     "1.0-2"      "0.95"    "7.2-31"     "1.3-1"     "2.0-1"
>        zoo        coin     mvtnorm  modeltools    survival
>    "1.2-2"     "0.5-2"     "0.7-5"    "0.2-10"      "2.30"
>>
>
>
>
>
>
>
>>
>> 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
>>
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>>
>>
>
>