----- Forwarded message from Joseph Kunkel -----
Date: Thu, 27 Sep 2012 09:18:42 -0400
From: Joseph Kunkel
Reply-To: Joseph Kunkel
Subject: Re: PCA of landmark data on wings
To: [email protected]
Jason,
The reversal of the sign of principal components is meaningless. It is the
separation of the components that matters. You will find that if you drop
records in the male or female set randomly you will get reversals of the sign
for individual components and it is of no significance as far as I am aware.
Joe
-·. .· ·. .><((((º>·. .· ·. .><((((º>·. .· ·. .><((((º> .··.· >=-
=º}}}}}><
Joseph G. Kunkel, Emeritus Professor
Biology Department
University of Massachusetts Amherst
Amherst MA 01003
http://www.bio.umass.edu/biology/kunkel/
On Sep 26, 2012, at 4:48 PM, [email protected] wrote:
>
> ----- Forwarded message from Jason Mottern -----
>
> Date: Wed, 26 Sep 2012 12:50:47 -0400
> From: Jason Mottern
> Reply-To: Jason Mottern
> Subject: PCA of landmark data on wings
> To: [email protected]
>
> Hello,
> I am a new list member, as well as a novice with respect to geometric
> morphometric analysis. I am doing a morphometric analysis of landmark data on
> wasp wings, and I'm doing both PCA and CVA. I am analyzing males and females
> separately, and there are three species. When I run all four analyses (CVA
> and PCA for each sex), the directions along the principal component axes are
> reversed for the female PCA analysis only. In other words, the signs are all
> reversed on the PC scores relative to the other three analyses, so its graph
> is "mirrored" compared to the other three. I am most intrigued as to why this
> reversal occurs between the female PCA and female CVA. These two analysis are
> based on the exact same set of partial warp scores, though, of course,
> subsequent calculations are different. I don't understand how the directions
> of the vectors are determined, and why they might differ between a PCA and
> CVA analysis of the same data. The programs I'm using for the analyses are PC!
AGen and CVAGen (Sheets, 2002). I apologize if I'm not articulating the
phenomenon very well, but, like I said, I'm very new to this stuff. Any
thoughts would be greatly appreciated.
> Cheers,
> Jason Mottern
> [email protected]
>
>
>
>
>
>
> ----- End forwarded message -----
>
>
>
>
----- End forwarded message -----
