That is not
surprising as the sign to attach to a PCA or CVA axis is arbitrary. Often
software reflects axes so that most of the loadings are positive but that is
again arbitrary. If you are running separate analyses but want the directions of
the axes to agree then you can simply reflect them so they match.
---------------------- F. James Rohlf,
John S. Toll Professor, Stony Brook University The
much revised 4th editions of Biometry and Statistical Tables are now
available: http://www.whfreeman.com/Catalog/product/biometry-fourthedition-sokal http://www.whfreeman.com/Catalog/product/statisticaltables-fourthedition-rohlf P Please consider the
environment before printing this email From:
[email protected]
[mailto:[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 PCAGen
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
----- Forwarded message from "F.
James Rohlf"
Date: Thu, 27 Sep
2012 17:59:01 -0400
From: "F. James Rohlf"
Reply-To: [email protected]
Subject: RE: PCA of landmark data on wings
To:
[email protected]
Sent: Wednesday,
September 26, 2012 4:49 PM
To:
[email protected]
Subject: PCA of landmark data on
wings
----- 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]
-----
End forwarded message -----
----- End
forwarded message
-----
- PCA of landmark data on wings morphmet_moderator
- RE: PCA of landmark data on wings morphmet_moderator
- RE: PCA of landmark data on wings morphmet_moderator
- Re: PCA of landmark data on wings morphmet_moderator
- RE: PCA of landmark data on wings morphmet_moderator
