The short answer is that a Poisson distribution is a discrete distribution: if that is appropriate to your data the rpart function (in the package of that name) has a suitable option.
On Mon, 28 Aug 2006, Solomon Dobrowski wrote: > Hello all. I have heard over and over that CART and its various tree-like > brethren are "non-parametric" techniques. When I read the chapter in > Chambers and Hastie on tree-based models it states that tree-based models > can be generalized (GTMs) in a manner similar to GLMs by specifying a > different deviance function to distributions other than the gaussian error > distribution ( section 9.4.3). I have an application in which the response > variable is a continuous variable representing tree counts within a unit > area and thus would be best described by a poisson distribution. The error > distribution for this data is not gaussian. If this is the case, will the > gaussian error distribution used in most regression tree packages, be > appropriate? Are there ways to specify the error distribution in R or Should > I log transform the response variable? If the specification of error > distribution in regression trees is important, than are these techniques > truly " non-parametric". Thanks for your inputs. > > > Solomon Dobrowski > Tahoe Environmental Research Center (TERC) > John Muir Institute of the Environment > University of California, Davis > 530 754 9354 > > > [[alternative HTML version deleted]] > > ______________________________________________ > R-help@stat.math.ethz.ch 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. > -- Brian D. Ripley, [EMAIL PROTECTED] 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 272866 (PA) Oxford OX1 3TG, UK Fax: +44 1865 272595 ______________________________________________ R-help@stat.math.ethz.ch 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.