-------- Original Message -------- Subject: RE: Sampe size reduction testing bootstrap Date: Wed, 27 May 2009 13:07:48 -0700 (PDT) From: Getulio Amaral <[email protected]> To: [email protected] References: <[email protected]> Dear Loius, The procedure that you want is subsamplig. See: "Politis and Romanos subsampling bootstrap takes samples without replacement of size b from the original sample of size n, generally with b < n (read b much less than n). Such samples are themselves samples of size b from the true unknown distribution F of the original sample." http://www.wepapers.com/Papers/8707/Subsampling_Bootstrap I can implement this procedure ir R but I do not use biological programs. The procedure can be easyly implemented. Best wishes, Getulio
-------- Original Message -------- Subject: RE: Sampe size reduction testing bootstrap Date: Wed, 27 May 2009 00:56:38 -0700 (PDT) From: Louis Boell <[email protected]> To: <[email protected]> References: <[email protected]> Dear Getulio, I have realized that "bootstrap" is indeed the inappropriate term for what I wish to do. I would simply like to randomly draw 15 specimens from my groups containing 30 specimens and to repeat this, say, 100 times in order to obtain a distribution of the Mahalanobis distances between groups containing only 15 specimens when using 15 Landmarks. Probably "permutation" fits this approach better. Concerning R, I am decided to learn it as soon as possible... Thanks for the advice, Best wishes, Louis Louis Boell MPI für Evolutionsbiologie August-Thienemannstr.2 24306 Plön [email protected] [email protected] > Date: Tue, 26 May 2009 15:23:03 -0400 > From: [email protected] > To: [email protected] > Subject: Re: Sampe size reduction testing bootstrap > > > > -------- Original Message -------- > Subject: Re: Sampe size reduction testing bootstrap > Date: Tue, 26 May 2009 11:37:03 -0700 (PDT) > From: Getulio Amaral <[email protected]> > To: [email protected] > References: <[email protected]> > > Dear Louis, > > The bootstrap uses a sample to a empirical distribution of the variable. > I do not think bootstrap is suitable in this case. > > Maybe you can use the Hotteling and Goodall tests on the tangent space > but the number of landmarks in each object must be the same. > > If you use R, there is the function shapes, where at the link > > http://cran.r-project.org/web/packages/shapes/index.html > > You can download the pdf file with all the instruction. > > Best regards, > Getulio J. A. Amaral > Departamento de Estatística > Centro de Ciências Exatas e da Natureza > Universidade Federal de Pernambuco > http://www.de.ufpe.br/~gjaa > > > -------- Original Message -------- > > Subject: Sampe size reduction testing bootstrap > > Date: Tue, 26 May 2009 07:40:35 -0700 (PDT) > > From: Louis Boell <[email protected]> > > To: <[email protected]> > > > > > > > > Dear colleagues, > > > > I would like to ask for your advice about the following problem: In a > > landmark-based GM context I am calculating Mahalanobis distances beween > > several groups. Now my material consists of museum material, thus I do > > have sample size problems. My samples consist of 15 to 30 Landmarks per > > group. I want to use 15 2D landmarks, which means that I need 30 > > specimens per group, which is not possible for some groups. In order to > > estimate the amount of deviation from the "true" Mahalanobis distances > > caused by having less than 30 specimens in a group, I randomly discarded > > 15 specimens from some groups for which I have 30 specimens and > > calculated the correlation between the Mahalanobis distances from the > > unreduced sample set and those from the reduced sample set, which gave > > me an rsq of about .8. > > Now I think that this calculation is in principle ok, but the choice of > > specimens to be discarded for the calculation of this correlation > > should be bootstrapped. I have been using MorphoJ so far, but this does > > not allow for implementig a self-written bootstrapping procedure (which > > I do also not yet have). What would you do in such a situation? > > Thanks in advance for any help with this, > > Best wishes, > > > > Louis Boell > > > > > > Louis Boell > > MPI für Evolutionsbiologie > > August-Thienemannstr.2 > > 24306 Plön > > [email protected] > > [email protected] > > > > > > > > ------------------------------------------------------------------------ > > Die virtuelle Festplatte im Netz - 25 GB für deine Bilder, Musikfiles > > und Dateien! Jetzt kostenlos sichern! > > <http://redirect.gimas.net/?n=M0905WLPhotos> > > > > -- > > Replies will be sent to the list. > > For more information visit http://www.morphometrics.org > > > > > Atenciosamente, > > > > > -- > Replies will be sent to the list. > For more information visit http://www.morphometrics.org > ------------------------------------------------------------------------ Kein Werbe-Blabla - hier klicken! <http://redirect.gimas.net/?n=M0905FTP_SpringCampaign1> -- Replies will be sent to the list. For more information visit http://www.morphometrics.org
Atenciosamente, Getulio J. A. Amaral Departamento de Estatística Centro de Ciências Exatas e da Natureza Universidade Federal de Pernambuco http://www.de.ufpe.br/~gjaa -- Replies will be sent to the list. For more information visit http://www.morphometrics.org
