Dear morphometricians, I'd like to have your precious advice about possible simple measures of shape variation for a sample in a multivariate space. I discussed about this with Prof. Rohlf about one year ago, and I know that it's hard to find a 'good analogue' of SD in univariate analyses. However, I liked the way Dr. Polly coped with this problem in his paper PALEOPHYLOGEOGRAPHY: THE TEMPO OF GEOGRAPHIC DIFFERENTIATION IN MARMOTS (MARMOTA) (J. Mammal., Volume 84, Number 2, 2003).
" Variation within samples was calculated as the mean of pairwise distances between individuals in a sample: ..... where dii was the multidimensional Euclidean distance between specimen i and i + 1 in sample x. This distance is analogous, but not equal to the sample standard deviation; dx is larger than the standard deviation." I wish to do something similar with average Procrustes distance (aPRD) in samples of marmot crania of different species (same landmark configuration in all samples, of course). I was wondering whether a ratio between aPRD in a species and aPRD in the pooled sample of all species could be used as an index of intraspecific variation compared to interspecific variation. Also, the same could be done to compare digitizing error (say, 10 digitizations of the same specimen) with biological variation in the sample under study (a marmot species or the pooled sample of all marmot species). Does it make any sense? If yes, are there any references on this topic? And, what are the caveats if aPRD is used as an approximate measure of variation in a sample? I thank you in advance all of you who may reply for your kind help. Please, let me know if you do not want that I redirect your answers to colleagues that may ask me to read them. All the best Andrea Andrea Cardini Istituto di Medicina Legale e delle Assicurazioni Universit degli Studi di Milano via Mangiagalli 37 Milano 20133, Italy tel. 0039 02 50315678/9 [EMAIL PROTECTED] and Division of Mammals, Department of Vertebrate Zoology NHB 390, MRC 108 National Museum of Natural History, Smithsonian Institution P.O. BOX 37012 Washington, DC 20013-7012, USA tel. 202 3571476 [EMAIL PROTECTED] ----------------------------------------------------- Salve, il messaggio che hai ricevuto stato inviato per mezzo del sistema di web mail interfree. Se anche tu vuoi una casella di posta free visita il sito http://club.interfree.it Ti aspettiamo! ----------------------------------------------------- == Replies will be sent to list. For more information see http://life.bio.sunysb.edu/morph/morphmet.html.
