-------- Original Message --------
Subject: MorphoJ and CVA
Date: Wed, 25 Apr 2012 13:46:30 -0400
From: Robert Ward <r.w...@bangor.ac.uk>
To: morphmet@morphometrics.org
Please forgive me if I'm making an obvious error. I'm trying to
reconcile different outputs relating to CVA results in MorphoJ.
The analysis is looking for sex differences in a 6-landmark shape and
the output from MorphoJ is shown below (I left out the Procrustes tests
and canonical coefficients). The MorphoJ output seems to suggest that
CVA was not able to find a set of shape features to make a highly
reliable discrimination, p=.06, not terrible but not great.
On the other hand, if I export the CV1 scores from that analysis, and
compare the male and female scores, then I get highly significant
differences with either a two-sample t-test, t(85)=3.8, p=.0002, or a
two-sample permutation test, Z=3.55, p=.0004.
So I reckon I am misunderstanding something somewhere. If CVA is finding
a vector through shape space that best discriminates the two groups, and
the CV1 score reflects position on this vector, then shouldn't it be
fine to test for a sex difference by a two-sample test of some kind? If
so, then I wonder why the big discrepancy between the MorphoJ results,
and tests using the CV1 scores?
Thanks for your help,
Rob
Canonical Variate Analysis: CVA x6 ... Sex
Dataset: mouthx6
Classification criterion: Sex
Groups Observations
1. F 40
2. M 48
Variation among groups, scaled by the inverse of the within-group variation
Eigenvalues % Variance Cumulative %
1. 0.16891938 100.000 100.000
Mahalanobis distances among groups:
F
M 0.8160
P-values from permutation tests (10000 permutation rounds) for
Mahalanobis distances among groups:
F
M 0.0621
