-------- Original Message --------
Subject: CVA in MorphoJ vs LDA in R
Date: Mon, 6 Jul 2009 08:34:07 -0700 (PDT)
From: Louis Boell <[email protected]>
To: <[email protected]>
Dear colleagues,
I encountered the following problem: in R, I performed least
discriminant analysis (lda) using as the argument Procrustes coordinates
calculated by procGPA . I then used the "predict" function to calculate
Mahalanobis distances between groups. I was, however, surprised to see
that the resulting Mahalanobis distances between groups do fundamentally
differ from those calculated using CVA in MorphoJ, based on the same set
of procrustes distances also calculated in R.
I had thought that LDA was close to being identical to CVA and had thus
expected very similar results. Did I omit an important step? As far as I
know, the procGPA coordinates have already been projected in the tangent
space, and first calculating a PCA and omitting the last four scores
should not much affect the results.
I have rechecked both my Procrustes coordinates and the grouping factor.
Everything seems fine.
Is there solmething fundamental I might be ignoring?
Thanks for advice, best wishes
Louis Boell
Louis Boell
MPI für Evolutionsbiologie
August-Thienemannstr.2
24306 Plön
[email protected]
[email protected]
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