One thing to check in such cases is whether a particular program is using the covariance or correlation matrix for the PCA.
I usually have students discuss PCA with me for ten minutes or so before I direct them (if they don't figure it out) to the fact that their stats software defaults to using the correlation matrix (reasonable for mixed variables) while the GM programs (dealing with commensurate vars) use the covariance mx. - hence, the different results. -dslice morphmet wrote: > Dear morphometricians, > > I'm doing some research on headshape dimorphism in European Eel using > elliptic Fourier analysis. > I've used the programs TPSUtil and TPSDig to get the coordinates of the > contours of the heads and then used the program PAST to analyze these > (with PCA). > I've also used the program Shape on the same specimens, but the results > were different. > > When I used Shape the first principal component explained about 48% of > the variance, but when I used PAST the first PC explained 66% of the > variance. > > Is there anyone who can explain this difference and maybe tell me which > method is the best to do a Fourier-analysis? > > Thank you in advance > Celine Ide > > > Ghent University > Evolutionary Morphology of Vertebrates > KL Ledeganckstraat 35 > B- 9000 Ghent > Belgium > +32 92645220 > [EMAIL PROTECTED] > > > -- Dennis E. Slice Department of Anthropology University of Vienna ======================================================== -- Replies will be sent to the list. For more information visit http://www.morphometrics.org
