Hi, I'm the author of PAST. The EFA algorithm in PAST
is the one described in this paper:
Ferson, S.F., F.J. Rohlf & R.K. Koehn. 1985.
Measuring shape variation of two-dimensional outlines.
Systematic Zoology 34:59-68
I don't know Shape. However, one possible source for
the difference is the standardization procedure -
whether, and if so how, the program standardizes for
size, rotation and the starting position for digitization.
Did you tick the "Invariant to rotation and starting
position" box in PAST?
And as Dennis Slice said - check whether the PCA
standardizes for variance ("PCA on the correlation
matrix").
It would also be interesting if you could test
Rohlf's EFA program, which should give similar
results as PAST (?).
Regards,
Oyvind Hammer
Natural History Museum
University of Oslo
On Thu, 7 Jun 2007, 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]
>
>
>
> --
> Replies will be sent to the list.
> For more information visit http://www.morphometrics.org
>
>
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