Dear Nathalia, if I remember well, PAST can give either distances between any pair of landmarks you are interested in or the matrix of distances between all possible pairs of landmarks (EDMA matrix). You can find PAST in the SUNY morphometric website. Also Morpheus can compute distances between pairs of landmarks.
Dear Asta, I totally agree with Prof. Rohlf about possible issues if you're using only a few PCs for doing a CVA. However, I would tend to think that if you're using enough PCs as to leave the relative positions of your specimens in the multivariate space virtually unchanged, you may be able to use a smaller number of PCs without losing important information. I haven't got the paper nearby and I might be doing a wrong citation (my apologies, if this is the case). However, it seems to me that Marco Corti and Carlo Fadda had a clever way to decide how many PCs to retain in the analysis not to change the spatial relationships of specimens. This was published in a paper in the 11th issue of Hystrix (2000). More or less, again if I remember well, they computed a matrix correlation between the Procrustes distance matrix and the matrix of Euclidean distances obtained using the first PCs. This was repeated many times progressively increasing the number of PCs used to compute the ED matrix (say that they started with 3, then 5, 10, 15, 20 etc.). Finally they plotted r against the number of PCs and used the plot to decide how many PCs had enough information as you would do in a scree plot. Of course, you may still end up with a number of PCs which is too large to be used in a CVA. Good luck. Cheers Andrea Dr. Andrea Cardini Lecturer in Biology Museo di Paleobiologia e dell'Orto Botanico Universitá di Modena e Reggio Emilia via Università 4, 41100, Modena, Italy tel: 0039 059 2056520 fax: 0039 059 2056535 & Hull York Medical School The University of York, Heslington, York YO10 5DD, UK E-mail address: [EMAIL PROTECTED], [EMAIL PROTECTED], [EMAIL PROTECTED] http://www.york.ac.uk/res/fme/people/andrea.htm -- Replies will be sent to the list. For more information visit http://www.morphometrics.org
