PCA of landmark data on wings

[morphmet_moderator]

----- 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: morphmet@morphometrics.org

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

jmott...@ucr.edu 

----- End forwarded message -----