----- Forwarded message from [email protected] ----- Date: Sun, 25 Nov 2012 16:56:58 -0800 From: [email protected] Reply-To: [email protected] Subject: Re: Do you need to know size for Procrustes superimposition? To: [email protected]
----- Forwarded message from al cardini ----- Date: Sun, 25 Nov 2012 06:23:46 -0500 From: al cardini Reply-To: al cardini Subject: Re: Do you need to know size for Procrustes superimposition? To: [email protected] Hi Patrick, if you're only interested in shape, scale should not matter. The GPA will standardized everything to unit centroid size regardless of the original units and all shape data will then be all in the same units of Procrustes shape distance. However, I would say that most of the time one may want to analyse both size and shape and for size you'll need to set the right scale factor for each picture (if taken with different magnifications) in TPSDig. If you knew already the scale factor, there might be tricks to rescale raw coordinates without setting the factor in each picture. I'd also consider that without measuring size, you might not be able to do much with allometry, which might or might not be interesting for your specific study. Be careful if you use shape coordinates in a standard statistical software. It might get the df of parametric tests wrong. If instead you use PCs with non-zero variance (eigenvalues), you'll have the same information on shape but can be confident about df being correct. If you then do pairwise tests of shape differences (for the same reason why you would do post-hoc tests in an ANOVA) using Procrustes shape distances and permutations (in MorphoJ, PAST etc.), there df will not matter, because it's not a parametric test. However, since you'll running multiple tests, you will have to take that into consideration when you interpret your P values. Good luck. Cheers Andrea On 24 November 2012 07:39, <[email protected]> wrote: > [email protected] -- NO DOCX, XLSX AND PPTX, PLEASE!!! COAUTHORS AND CONTRIBUTORS, PLEASE, FOR SHARING FILES, CONVERT THEM IN DOC, XLS (UNLESS LONGER THAN 256 COLUMNS) AND PPT Dr. Andrea Cardini Researcher in Animal Biology Dipartimento di Scienze Chimiche e Geologiche, Università di Modena e Reggio Emilia, l.go S. Eufemia 19, 41121 Modena, Italy Honorary Fellow Functional Morphology and Evolution Unit, Hull York Medical School University of Hull, Cottingham Road, Hull, HU6 7RX, UK University of York, Heslington, York YO10 5DD, UK Adjunct Associate Professor Centre for Forensic Science , The University of Western Australia 35 Stirling Highway, Crawley WA 6009, Australia E-mail address: [email protected], [email protected], [email protected], [email protected] Webpage: http://sites.google.com/site/hymsfme/drandreacardini Datasets: http://ads.ahds.ac.uk/catalogue/archive/cerco_lt_2007/overview.cfm#metadata Editorial board for: Zoomorphology: http://www.springer.com/life+sciences/animal+sciences/journal/435 Journal of Zoological Systematics and Evolutionary Research: http://www.wiley.com/bw/journal.asp?ref=0947-5745&site=1 Hystrix, the Italian Journal of Mammalogy: http://www.italian-journal-of-mammalogy.it/ ----- End forwarded message ----- ----- End forwarded message -----
