Re: MorphoJ: PLS vs Modularity hypothesis

[morphmet]

-------- Original Message --------
Subject:        Re: MorphoJ: PLS vs Modularity hypothesis
Date:   Thu, 05 Nov 2009 11:02:11 +0100
From:   carlo.mel...@unina.it
To:     morphmet <morphmet_modera...@morphometrics.org>
References:     <4aef15fb.5070...@morphometrics.org>



Dear Javier,

PLS does not allow you to test for modularity. It will maximise the
covariation between two block of variables that you can assume they
could be modules. But a strong correlation does not mean that they are
modules. The PLS will extract pairs of SA (which are vectors: Singular
Axis) that are associated with an SV (Singular Value) extracted from a
Singular Value Decomposition (basically the Singular Values describe the
amount of covariance explained by each pair of SA).

I strongly suggest you to read:  "/Rohlf F.J., Corti M. 2000. Use of
two-block partial least squares to study covariation in shape.
Systematic Biology 49: 740?753." where the tecnique is explained much
better than I did./

Probably you want to test for modularity through Morphoj and the
Escoufier index (RV, Escoufier 1973) that is different metric not
entirely correlated with PLS. Check

Klingenberg, C. P. 2009. Morphometric integration and modularity in
configurations of landmarks: Tools for evaluating a-priori hypotheses.
Evolution & Development 11:405?421.

where you can found more info on how to test for modularity.

Good luck and if you need the pdf just ask. The Klingenbergh pdf is
linked in MorphoJ help manual.

All the best

Carlo Meloro



Quoting morphmet <morphmet_modera...@morphometrics.org>:

 >
 >
 > -------- Original Message --------
 > Subject:         MorphoJ: PLS vs Modularity hypothesis
 > Date:         Sun, 1 Nov 2009 06:13:43 -0800 (PST)
 > From:         Javier Santos <javiersant...@hotmail.com>
 > To:         <morphmet@morphometrics.org>
 >
 >
 >
 > Hello everybody,
 >
 > I had a doubt considering how to correctly interpret the RV coefficient
 > given in MorphoJ when doing PLS and Modularity hypothesis analysis.
 > Should the RV coefficient given in PLS analysis be interpreted the same
 > as the RV coefficient in the Modularity hypothesis? So, should low RV
 > coefficients given in PLS analysis with significant p-values be
 > considered as support that blocks constitute seperate modules? Also, can
 > someone give any more info on how these two analysis differ when
 > studying morphological integration and modularity, apart from the fact
 > that in PLS modules are chosen a priori. Thank you.
 >
 >
 > All the best,
 > Javier Santos
 > jssan...@usal.es <mailto:jssan...@usal.es>
 > University of Salamanca
 >
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