But in that paper they refer to another (http://www.bepress.com/cgi/viewcontent.cgi?article=1053&context=ucbbiostat) where they say that "permutation distribution produces an asymptotically correct null distribution if (i) the sample sizes are equal...". Best regards, João
________________________________ De: Achim Zeileis [mailto:[EMAIL PROTECTED] Enviada: qua 09-04-2008 0:26 Para: João Fadista Cc: ONKELINX, Thierry; r-help@r-project.org Assunto: Re: [R] permutation test assumption? On Wed, 9 Apr 2008, João Fadista wrote: > Dear Thierry, > > Thanks for the reply. But as you may read in the paper > http://bioinformatics.oxfordjournals.org/cgi/content/abstract/22/18/2244 > when the sample sizes are not the same there may be an increase in the > Type I error rate. No, this is false and not what the reference above says. Please read more carefully. > Comments will be appreciated. The basic assumption for permutation tests is exchangeability of the observations (regardless of sample sizes). The reference above describes a situation when this assumption is violated. Z > Best regards, > João Fadista > > > ________________________________ > > De: ONKELINX, Thierry [mailto:[EMAIL PROTECTED] > Enviada: ter 08-04-2008 15:27 > Para: João Fadista; r-help@r-project.org > Assunto: RE: [R] permutation test assumption? > > > > Dear João, > > You can do permutation tests on an unbalanced design. > > HTH, > > Thierry > > > ---------------------------------------------------------------------------- > ir. Thierry Onkelinx > Instituut voor natuur- en bosonderzoek / Research Institute for Nature and > Forest > Cel biometrie, methodologie en kwaliteitszorg / Section biometrics, > methodology and quality assurance > Gaverstraat 4 > 9500 Geraardsbergen > Belgium > tel. + 32 54/436 185 > [EMAIL PROTECTED] > www.inbo.be > > To call in the statistician after the experiment is done may be no more than > asking him to perform a post-mortem examination: he may be able to say what > the experiment died of. > ~ Sir Ronald Aylmer Fisher > > The plural of anecdote is not data. > ~ Roger Brinner > > The combination of some data and an aching desire for an answer does not > ensure that a reasonable answer can be extracted from a given body of data. > ~ John Tukey > > -----Oorspronkelijk bericht----- > Van: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] Namens João Fadista > Verzonden: dinsdag 8 april 2008 15:18 > Aan: r-help@r-project.org > Onderwerp: [R] permutation test assumption? > > Dear all, > > Can I do a permutation test if the number of individuals in one group is much > bigger than in the other group? I searched the literature but I didin´t find > any assumption that refers to this subject for permutation tests. > > > Best regards > > João Fadista > Ph.d. student > > > > UNIVERSITY OF AARHUS > Faculty of Agricultural Sciences > Dept. of Genetics and Biotechnology > Blichers Allé 20, P.O. BOX 50 > DK-8830 Tjele > > Phone: +45 8999 1900 > Direct: +45 8999 1900 > E-mail: [EMAIL PROTECTED] <mailto:[EMAIL PROTECTED]> > Web: www.agrsci.org <http://www.agrsci.org/> > ________________________________ > > DJF now offers new degree programmes > <http://www.agrsci.org/content/view/full/34133> . > > News and news media <http://www.agrsci.org/navigation/nyheder_og_presse> . > > This email may contain information that is confidential. Any use or > publication of this email without written permission from Faculty of > Agricultural Sciences is not allowed. If you are not the intended recipient, > please notify Faculty of Agricultural Sciences immediately and delete this > email. > > > > > [[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 > and provide commented, minimal, self-contained, reproducible code. > > ______________________________________________ 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.
