Dave, Thanks for the advice. I'll take a look at MANOVABOARD
Craig >>> [EMAIL PROTECTED] 04/19/05 7:31 AM >>> Dear Craig- It sounds to me like you need to do a MANCOVA, and analyze the dependence of shape on both a grouping variable and a size variable. This will let you know if there is a dependence of size on shape, of size on group membership and if there is an interaction of group x size (meaning different dependencies of shape on size in the two groups). Fred Bookstein outlined a resampling approach to this issue in a morphmet posting a while back. You may get some other responses on morphmet related to that approach. I wrote a piece of software (called Manovaboard, I'm afraid) that carries out resampling based MANOVA and MANCOVA of shape data, using one covariate and one or two group variables. This piece of software attempts to use the approach outlined by Bookstein. I haven't published any results based on it yet , but if you are interested, go ahead and use it. To the best of my knowledge it is working correctly. It is part of my IMP series software which may be found at http://www2.canisius.edu/~sheets/morphsoft.html and/or http://www2.canisius.edu/~sheets/moremorph.html You may need several pieces of IMP software in addition to Manovaboard, including CoordGen, which allows you to change file formats. You can also do the Mancova based on partial warp scores using Jim Rohlf's tpsRegress program. tpsRegress is a very nice piece of software, we just found it a bit daunting to do complex Mancova analyses with it, your question is relatively straightforward. Best wishes- Dave Sheets ---- Original message ---- >Date: Mon, 18 Apr 2005 14:58:15 -0700 >From: "Craig Busack" <[EMAIL PROTECTED]> >Subject: Thin Plate Splines and Size >To: <[email protected]> > >Morphometricians, > >I'm looking for shape differences between two groups of fish. My plan was to do a MANOVA of partial warp scores, and then canonical variate analysis to explore the shape differences. I have just learned, however, that my groups of fish differ in size (about 0.5 SD), so now am wondering how to evaluate how much of the shape difference I see (and based on preliminary analysis, it is enough to classify fish by CVA with about 95% accuracy) is actually due to size differences. I realize this may be an elementary question, but what's the best way to get at this problem? The guidance I have so far says that multivariate regression of partial warps on centroid is the best way to begin. > >Thanks > >Craig Busack >Washington Department fo Fish and Wildlife > > H. David Sheets, PhD Dept of Physics, Canisius College 2001 Main St Buffalo NY 14208
