-------- 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]
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Atenciosamente,
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