Thank you all for your good advices and codes. I know really that I have huge deficits in statistics knowledge and I am really working on it, but its not done in five minutes.
Anyway thank you very match for your help. Greets Birgit Am 07.02.2008 um 17:34 schrieb Gavin Simpson: > On Thu, 2008-02-07 at 11:16 -0400, tyler wrote: >> On Thu, Feb 07, 2008 at 02:36:58PM +0000, Gavin Simpson wrote: >>> >>> But I'm not sure this matters much. If you use the formula >>> interface to >>> lda(), factors get expanded to the dummy variables Tyler is talking >>> about. But of course, a factor with two levels 0/1 doesn't need much >>> manipulation as you only need a single dummy variable to >>> represent its >>> two states: >>> >> >> Thanks, Gavin! >> >> R's formula interface if very powerful, and I'm just starting to >> understand how to take full advantage of it. >> >>> You might want to standardise your exp variables to zero mean and >>> unit >>> variance prior to doing the lda so that all variables carry the same >>> weight, if you have mixtures of numeric (continuous) variables and >>> binary ones. >> >> This is the part I was unsure of. If you have a categorical >> explanatory variable with five levels, you can turn it into four >> dummy >> variables, which you then standardize. Does the original variable end >> up getting four times the weight of a single numerical variable? > > I have no idea Tyler. I would take great heed in the warning about > using > only continuous variables in lda() - the author(s) of that function > certainly know what they are talking about! One is probably violating > some of the underlying assumptions of the method using > binary/categorical data. > > There are better classification tools available than LDA for mixed > data > like this, such as a classification tree, which is easy to interpret > (always good for ecologists ;-) or some of the bagging, boosting or > random forest algorithms also spring to mind. There has been quite > a lot > on these techniques in the ecological literature in the past 3-4 > years. > > HTH > > G > >> >> Cheers, >> >> Tyler >> > -- > %~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~% > Dr. Gavin Simpson [t] +44 (0)20 7679 0522 > ECRC, UCL Geography, [f] +44 (0)20 7679 0565 > Pearson Building, [e] gavin.simpsonATNOSPAMucl.ac.uk > Gower Street, London [w] http://www.ucl.ac.uk/~ucfagls/ > UK. WC1E 6BT. [w] http://www.freshwaters.org.uk > %~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~% > > ______________________________________________ > 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 > and provide commented, minimal, self-contained, reproducible code. Birgit Lemcke Institut für Systematische Botanik Zollikerstrasse 107 CH-8008 Zürich Switzerland Ph: +41 (0)44 634 8351 [EMAIL PROTECTED] 175 Jahre UZH «staunen.erleben.begreifen. Naturwissenschaft zum Anfassen.» MNF-Jubiläumsevent für gross und klein. 19. April 2008, 10.00 Uhr bis 02.00 Uhr Campus Irchel, Winterthurerstrasse 190, 8057 Zürich Weitere Informationen www.175jahre.uzh.ch ______________________________________________ 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 and provide commented, minimal, self-contained, reproducible code.
