morphmet
Thu, 12 Nov 2009 06:47:13 -0800
-------- Original Message -------- Subject: Re: permutation test for shape trajectory between sexes Date: Wed, 11 Nov 2009 00:30:19 -0800 (PST) From: Dean Adams <dcad...@iastate.edu> To: morphmet@morphometrics.org References: <4af9a02c.6090...@morphometrics.org> Stefan, Yes, assessing the angle between vectors is the way to go. A general approach for determining whether phenotypic trajectories differ is to first run a factorial MANOVA, with population and sex as main effects, along with a pop*sex interaction term. A significant interaction term implies that the sexual dimorphism vectors are not consistent between populations. However, be aware that for multivariate data, a significant interaction term could mean a number of things. For instance, it could be that the direction of sexual dimorphism is consistent between populations, but the amount (magnitude) of sexual dimorphism is greater in one population than it is in the other. Alternatively, the two populations could have similar magnitudes of sexual dimorphism, but be oriented in different directions. Finally, both the magnitude and direction of sexual dimorphism could differ. As such you need to run several additional analyses to investigate these possibilities. We recently developed an analytical approach for assessing such patterns in multivariate vectors and trajectories. Our approach quantifies attributes of phenotypic trajectories (magnitude, orientation, etc.) and statistically assesses them using residual randomization. The paper describing the general approach is: Adams, D.C., and M.L. Collyer. 2009. A general framework for the analysis of phenotypic trajectories in evolutionary studies. /Evolution/. 63:1143-1154. and earlier papers: Collyer, M. L., and D. C. Adams. 2007. Analysis of two-state multivariate phenotypic change in ecological studies. /Ecology/. 88:683-692. Adams, D. C., and M.L. Collyer. 2007. Analysis of character divergence along environmental gradients and other covariates. /Evolution/. 61:510-515. All of these papers are available on my web page. Additionally, there is some R code associated with the 2009 paper for implementing the approach. Hope this helps. Dean Dr. Dean C. Adams Associate Professor Department of Ecology, Evolution, and Organismal Biology Department of Statistics Iowa State University Ames, Iowa 50011 At 06:17 PM 11/10/2009, you wrote:
-------- Original Message -------- Subject: permutation test for shape trajectory between sexes Date: Tue, 10 Nov 2009 05:39:12 -0800 (PST) From: Stefan Schlager <stefan.schla...@uniklinik-freiburg.de> To: morphmet@morphometrics.org References: <4af5219d.1070...@morphometrics.org> Dear all, I am currently working on mandibles of two populations and I want to prove,that there is no common trajectory explaining sexual dimorphism in both populations. Analyzing the PCs of the pooled data implied the ladder- or at least that there is no common separator between sexes along the axis of the PC coordinate system. I now wonder, if I could prove this hypothesis by a permutation test on the angle of the residual vectors (in the PC coord. syst) between the sexes means of the two populations. What I thought was: if the trajectory was about the same, it means that the residual vector between the sexes' means should point roughly into the same "direction". -and if this angle is larger for the actual populations compared to those of randomly assigned populations, this would proof my hypothesis. Am I completely misleaded, or could this work? Many thanks Stefan -- Stefan Schlager M.A. Medizinische Fakultät - Anthropologie Hebelstr. 29 79104 Freiburg Tel: +49(0)761/203-5522 Fax: +49(0)761/203-6898 -- Replies will be sent to the list.For more information visit http://www.morphometrics.org <http://www.morphometrics.org/>
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