Biology Reference
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TABLE 7.1 Variance Explained By Each PC Axis of the Human Dentition Data Set, With a Description of
the Pattern Implied By the Axis
PCA
Axis
Percent of Variance
Pattern Implied By the Axis
1
Mandible: 54.0
Maxillary: 39.8
Arch width-positive scores indicate a relatively wide arch, negative scores
indicate a relatively narrow arch, in both maxillary and mandible
2
Mandible: 8.8
Maxillary: 12.6
Positive scores indicate a labial displacement of both central incisors, relative to a
lingual displacement of both lateral incisors, with a slight labial shift of the
canines in the maxillary
3
Mandible: 6.7
Maxillary: 7
This axis implies a pattern of left
right asymmetry in both maxillary and
mandible, although the specific details of the asymmetry differ. In the mandible,
there is a “bulge” of all teeth to one side, whereas in the mandible, all 4 incisors
shift in a line relative to the canines
4
Mandible: 4.2
Maxillary: 5.2
Asymmetry in the location of the central incisors in the mandible. One shifted
lingually and the other labially, while the adjacent lateral incisors shift in the
opposite directions. In the maxillary, this is a different pattern, a labial shift of
one central incisor with an accompanying lingual shift of the lateral incisor and
canine
5
Mandible: 3.9
Maxillary: 4.8
In the mandible, this axis implies opposing lateral and lingual shifts of the central
incisors, while in the maxillary, this axis describes outward shifts of both canines
6
Mandible: 3.6
Maxillary: 3.8
Opposing lingual
labial shifts of the canines and lateral incisors appear in the
maxillary, while asymmetric lingual
labial shifts appear in the two lateral
incisors of the maxillary, with some changes in the orientation of one canine
Note that the descriptions are stated in terms of positive scores, negative scores simply reverse the pattern.
TABLE 7.2 Covariance Explained by Each PLS Axis of the Human Dentition Data Set, with a Description
of the Pattern Implied by the Axis
PLS
Axis
Percent of
Covariance
Pattern Implied By the Axis
1
65.4
A contrast between wide and narrow arches
2
7.2
Strong labial displacement of both central incisors of both the upper and lower
dentition.
3
5
Strong left-right asymmetry pattern
4
4.3
Opposing tilts of the central incisors and lateral incisors of both maxillary and
mandible, and minor amounts of rotation of the canines
correlated, we then need to determine whether the observed covariance is lower than we
would obtain between two randomly partitioned subsets of landmarks that have the same
number of landmarks as the a priori partitions. Our second objective is to describe the
dominant axes of covariation between the two modules should they covary.
Using the first approach, we obtain an RV coefficient which, as you recall, is analogous
to an R 2 , of 0.506. For an R 2 , this is a very high value; not surprisingly, the null hypothesis
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