-------- Original Message -------- Subject: RE: MorphoJ problem: erroneous canonical coefficients? Date: Mon, 5 Mar 2012 14:42:13 -0500 From: F. James Rohlf <ro...@life.bio.sunysb.edu> Reply-To: <ro...@life.bio.sunysb.edu> Organization: Stony Brook University To: <morphmet@morphometrics.org> However, isnt the goal the visualization of the group mean differences? The CV vectors are not expected to be biologically meaningful in themselves - just as the individual PCs are not of interest in themselves. - - - - - - - - - - - - - - - - - - - - - - - - - - - - - F. James Rohlf, John S. Toll Professor Stony Brook University
-----Original Message----- From: morphmet [mailto:morphmet_modera...@morphometrics.org] Sent: Monday, March 05, 2012 5:14 AM To: morphmet Subject: Re: MorphoJ problem: erroneous canonical coefficients? -------- Original Message -------- Subject: Re: MorphoJ problem: erroneous canonical coefficients? Date: Mon, 5 Mar 2012 06:01:43 -0500 From: Philipp Mitteröcker <mitte...@univie.ac.at> To: morphmet@morphometrics.org This is an interesting issue raised by Chris. In a recent paper, we
explained
why shape changes corresponding to CVs should be visualized based on the CV coefficients, just as for PCA. They are vectors in tangent space. For
two
groups, the regression approach advocated by Chris leads to a
visualization of
the group mean difference vector, not the CV. I am aware that this is a controversial topic and I am happy to discuss
it!
Mitteroecker P, Bookstein FL (2011) Classification, linear discrimination,
and
the visualization of selection gradients in modern morphometrics. Evolutionary Biology 38, 100-114 Best wishes, Philipp Am 04.03.2012 um 15:56 schrieb morphmet: > > > -------- Original Message -------- > Subject: Re: MorphoJ problem: erroneous canonical coefficients? > Date: Wed, 29 Feb 2012 06:38:43 -0500 > From: Chris Klingenberg <c...@manchester.ac.uk> > Reply-To: c...@manchester.ac.uk > Organization: University of Manchester > To: morphmet@morphometrics.org > > Dear Louis > > There is nothing erroneous with the canonical coefficients provided by > MorphoJ, as far as I know. > > The way you phrase your query suggests that you expect that the shape > changes associated with canonical variates (CVs) are just a scaled > version of the CV coefficients, as it holds for principal components. > This expectation is mistaken, because it misses the crucial difference > that CVs are not computed in shape (tangent) space itself, but in a > transformed space. > > This problem has been extensively discussed in geometric morphometrics. > The computations of shape changes associated with CVs that are used in > MorphoJ are based on the solution proposed by Rohlf et al. (1996): > Rohlf, F. J., A. Loy, and M. Corti. 1996. Morphometric analysis of Old > World Talpidae (Mammalia, Insectivora) unsing partial-warp scores. Syst. > Biol. 45:344362. > > More discussion on transformed spaces and discriminant/canonical > variate analysis can be found here: > Klingenberg, C. P., and L. R. Monteiro. 2005. Distances and directions > in multidimensional shape spaces: implications for morphometric > applications. Syst. Biol. 54:678688. > > I hope this is useful. > > Best wishes, > Chris > > > > On 2/27/2012 5:23 PM, morphmet wrote: >> >> >> -------- Original Message -------- >> Subject: MorphoJ problem: erroneous canonical coefficients? >> Date: Thu, 23 Feb 2012 08:18:03 -0500 >> From: Louis Boell <lbo...@evolbio.mpg.de> >> To: morphmet@morphometrics.org >> >> Dear colleagues, >> >> I am encountering a peculiar problem in MorphoJ: after performing >> CVA, the Canonical Coefficients given in the results do not >> correspond at all to the vector lengths in the lollipop shape change >> graphs. Either the graphs or the Coefficients appear to be erroneous, >> because they contradict each other. This only happens with CVA, not >> with PCA, for which the results are nicely congruent. Did anyone else encounter this? >> Any explanation? >> Thanks for any help >> Best regards, >> >> Louis >> >> > > -- > ********************************************************** ***** > Christian Peter Klingenberg > Faculty of Life Sciences > The University of Manchester > Michael Smith Building > Oxford Road > Manchester M13 9PT > United Kingdom > > Telephone: +44 161 275 3899 > Fax: +44 161 275 5082 > E-mail: c...@manchester.ac.uk > Web: http://www.flywings.org.uk > Skype: chris_klingenberg > ********************************************************** ***** > > ___________________________________ Dr. Philipp Mitteroecker Department of Theoretical Biology University of Vienna Althanstrasse 14 A-1090 Vienna, Austria Tel: +43 1 4277 56705 Fax: +43 1 4277 9544 email: philipp.mitteroec...@univie.ac.at homepage: http://theoretical.univie.ac.at/people/mitteroecker
