Dear Andrea,
In principle, I agree that one should avoid interpreting single landmarks or shape coordinates because - landmarks are not geometrically independent after GPA (loss of degrees of freedom) - landmark displacement vectors depend on the superimposition and, hence, the other landmark positions (Pinocchio effect) - often the shape features are not that local but involve a joint shift of multiple landmarks; in this case, the actual shape patterns cannot be inferred from looking at each landmark separately. Formal statistical analyses (e.g., regressions, significance tests) of each landmark or shape coordinate separately can hardly be interpreted and are subject to the multiple comparison problem. This is why we have multivariate stats and GMM. With proper visualizations, such as TPS deformation grids or series of reconstructed shapes, the Pinocchio effect does not apply and one can observe even complex shape or form differences. Of course, there can be exceptions and a biological signal can be local and be represented well by a single landmark or a single interlandmark distance. But one cannot know about this before analyzing all the landmarks jointly! Best, Philipp Mitteroecker On Tuesday, May 11, 2021 at 6:18:33 PM UTC+2 [email protected] wrote: > Dear Dr. Andrea, Fruciano, and Pietro, > > I asked a question on integration/modularity in geomorph google forum. I > benefit hugely from Mike's reply. > > That post is somewhat related to the current post. So I am here to let you > aware and please feel free to comment further there if you have interest. > > Link to my question: > https://groups.google.com/u/3/g/geomorph-r-package/c/VKpAxHnVW1U > > On Tuesday, May 11, 2021 at 7:52:05 PM UTC+8 Carmelo Fruciano wrote: > >> Dear Andrea, >> I've seen this from time to time, but I am not too sure there's been a >> recent increase in this. >> >> Some of the most striking cases in my own literature searches and >> reading involve genetic mapping of one coordinate at a time (post-GPA) - >> as if each coordinate were a separate trait, which is (IMHO) nonsensical. >> This is obviously biased because of my own research interests (i.e., I >> have seen more in this area because I've read a bit more in this area >> than in others, not because they are more frequent in genetic mapping >> than in other areas). But these papers are fairly spread over time and I >> didn't catch any particular increase in their frequency as of late. >> >> I understand this does not exactly address what you were asking but I >> still hope it helps, >> Carmelo >> >> >> -- >> ================== >> Carmelo Fruciano >> Italian National Research Council (CNR) >> IRBIM Messina >> http://www.fruciano.org/ >> ================== >> >> >> On 10 May 2021 14:49, andrea cardini <[email protected]> wrote: >> >> Dear All, >> I have the impression that studies analyzing one landmark at a time >> after a Procrustes superimposition (plus a possible sliding of >> semilandmarks) are beginning to pop up here and there in the biological >> literature. >> I wonder whether there's some revolutionary evidence, which was >> published and I missed, that contradicts a most basic principle of >> Procrustes shape analysis: never to analyze Procrustes shape variables >> one at a time, including especially the case of pairs or triplets of >> 2D-3D landmark Procrustes shape coordinates. This is nicely summarized >> by Paul in J. Anat. (2000) 197, pp. 103–120; exemplified in Fig. 9 of >> doi:10.1371/journal.pone.0025630; related to the problem of analyzing >> one PW at a time discussed by Jim (Syst. Biol. 47(1):147± 158, 1998); >> and most likely known since the early days of Procrustes GMM. >> I would be astonished to find that this is not longer true but I am >> happy to be surprised. >> >> Many thanks in advance for refs and feedback. >> Please, if you reply directly to me, let me know if I can share your >> answer. >> >> Cheers >> >> Andrea >> >> >> >> >> -- >> Dr. Andrea Cardini >> Researcher, Dipartimento di Scienze Chimiche e Geologiche, Università di >> Modena e Reggio Emilia, Via Campi, 103 - 41125 Modena - Italy >> tel. 0039 059 4223140 >> >> Adjunct Associate Professor, Centre for Forensic Anthropology, The >> University of Western Australia, 35 Stirling Highway, Crawley WA 6009, >> Australia >> >> E-mail address: [email protected], [email protected] >> WEBPAGE: https://sites.google.com/view/alcardini2/ >> or https://tinyurl.com/andreacardini >> >> FREE Yellow BOOK on Geometric Morphometrics: >> https://tinyurl.com/yellowmorphobook >> >> ESTIMATE YOUR GLOBAL FOOTPRINT: >> http://www.footprintnetwork.org/en/index.php/GFN/page/calculators/ >> SUPPORT: secondwarning.org >> >> -- >> You received this message because you are subscribed to the Google Groups >> "Morphmet" group. >> To unsubscribe from this group and stop receiving emails from it, send an >> email to [email protected]. >> To view this discussion on the web visit >> https://groups.google.com/d/msgid/morphmet2/7e5da2bd-3026-12df-522e-a17eed006d24%40gmail.com. >> >> >> >> >> -- You received this message because you are subscribed to the Google Groups "Morphmet" group. 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