Dear morphometricians, I greatly enjoyed the discussion on MDS, which reminded me about a similar discussion on MANOVA/MANCOVA, DA and related techniques that we had in MORPHMET about one year and half ago. In that case also the discussion was about how appropriate (or inappropriate) is to use multivariate methods, which have been routinely employed in traditional morphometrics, in the analyses of geometric morphometric data. That issue (use of MANOVA etc. for GMM analyses) has been recently discussed by Klingenberg & Monteiro (2005, Syst. Biol., 54: 678-688). Not everybody will agree with them, probably, but I found their explanations extremely clear and very helpful. I haven't got anything particularly interesting to add to the discussion on MDS. Personally, I used it a few times when my only purpose was to find the ordination which best summarized similarity relationships among specimens to visualize them in a 2D or 3D scatterplot. At least sometimes, the matrix correlation between the matrix of Procrustes distances and the matrix of Euclidean distances computed using the MDS axes seems to be slightly higher than the correlation between the PRD matrix and the matrix of Euclidean distances computed using the first (2 or 3) PCs. Whether this improvement is negligible and PCA should be preferred anyway, given the issues with MDS discussed by Prof. Bookstein, I cannot say. I strongly hope to have soon more papers like Klingenberg & Monteiro (2005), or Rohlf (1998, Syst. Biol., 47:147-158), that may provide us with clear explanations on otherwise rather difficult issues and that may act as guidelines in a form accessible not only to statisticians. It seems to me that GMM has indeed been a revolution (Rohlf & Marcus, 1993, TREE, 8:129-132), but after more than 10 years from that paper there are still some (or several) issues that needs to be discussed and clarified, hopefully in a way that everybody with a basic knowledge of statistics can understand. That there are still topics open to discussion was recently suggested to me also by reading in Fink et al. (2005, Proc. R. Soc. B, 272: 1995-2001) that a regression was done using the first five pairs of PWS, contrary to the common view, expressed also by Prof. Bookstein, that PWS should be used as a joint set and not as separate variables. However, there might be exceptions to this commonly accepted 'rule', which I do not understand but I'd like to. I wonder whether it might be time to try to organize a morphometric workshop on these and similar issues. Thanks in advance for your comments and advice. Cheers
Andrea Dr. Andrea Cardini Hull York Medical School The University of York, Heslington, York YO10 5DD, UK & The University of Hull,Cottingham Road, Hull HU6 7RX, UK tel. 01904 321752 fax 01904 321696 E-mail: [EMAIL PROTECTED] http://www.york.ac.uk/res/fme/people/andrea.htm ------------------------------------------------------------------------- Visita http://domini.interfree.it, il sito di Interfree dove trovare soluzioni semplici e complete che soddisfano le tue esigenze in Internet, ecco due esempi di offerte: - Registrazione Dominio: un dominio con 1 MB di spazio disco + 2 caselle email a soli 18,59 euro - MioDominio: un dominio con 20 MB di spazio disco + 5 caselle email a soli 51,13 euro Vieni a trovarci! Lo Staff di Interfree ------------------------------------------------------------------------- -- Replies will be sent to the list. For more information visit http://www.morphometrics.org
