-------- 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
