-------- Original Message -------- Subject: Re: Comparing Segments of Developmental Trajectories Date: Tue, 13 Mar 2012 04:42:44 -0400 From: Carmelo Fruciano <[email protected]> To: [email protected] morphmet <[email protected]> ha scritto:
-------- Original Message -------- Subject: Comparing Segments of Developmental Trajectories Date: Mon, 12 Mar 2012 18:15:09 -0400 From: Michelle Singleton <[email protected]> To: [email protected] Dear Colleagues, As part of a study of ontogenetic shape change in a group of related species, I wish to compare patterns of shape change between successive developmental stages. My intention was to compare angular differences between species vectors obtained from multivariate regression of Procrustes residuals on my developmental variable. When I apply this approach to the full developmental series (juvenile to adult) I get interspecies angles comparable to those obtained by myself and others in prior studies, but when I look at individual segments (e.g., Stage 1 to Stage 2) the resulting angles are very large, apparently because the amount of variation between stages is too small to allow accurate vector estimates, although the smaller sample sizes probably contribute as well. The large angles do, nevertheless, return the same qualitative result (in terms of relative vector similarity) as the angles for the full ontogenetic series. My questions are: 1) have I correctly identified the source of the discrepancy in angle magnitudes? 2) can permutation significance tests based on these angles be meaningful; or, 3) is this the wrong approach and is there perhaps a more appropriate method for this comparison?
Dear Michelle, maybe I'm wrong and I didn't properly understand the question but couldn't it be that the real trajectories are non linear and that's why you obtain different results when you apply a single regression (a single line) and when you compute separate vectors between stages? Just my two cents... Carmelo -- Carmelo Fruciano Post-doc - University of Konstanz - Konstanz, Germany Honorary Fellow - University of Catania - Catania, Italy e-mail [email protected] http://www.fruciano.it/research/ ---------------------------------------------------------------- Universita' di Catania - A.P.Se.Ma. Servizio di Posta Elettronica
