Further Applications of EDMA - An Invariant Approach to Statistical Analysis of Shapes - page 265

to “left” or “right”).
The landmarks describing cranial form include three pairs of bilat-
eral landmarks and four midline landmarks. The midline landmarks
are found on the face (nasion — NAS) and the basicranium (sella —
SEL; basion — BAS; opisthion — OPI). The bilateral landmarks are
found on the lateral rim of the orbit (frontozygomatic junction — FZJ)
and on the most lateral aspect of the basicranium (external auditory
meatus — EAM; asterion — AST). In the descriptions that follow, the
landmark names will be prefixed with either “f ”, denoting the side that
is prematurely fused, or “u”, denoting un fused. To compute the asym-
metry vector A , the fused-side measurements will be divided
(elementwise) by the unfused-side measurements: A = F / U . Elements
of A that are greater than 1 indicate measurements that tend to be
larger on the fused side. In contrast, elements of A that are less than 1
indicate measurements that are smaller on the fused side.
The asymmetry vector ( A ) is shown in Table 7.1 , along with 90%
marginal confidence intervals that were computed using 100 nonpara-
metric bootstrap resamples. Nearly all of the ratios are less than 1,
indicating that the fused side of the cranium tends to be smaller than
the unfused side ( Figure 7.3 ) . Many of these ratios have confidence
intervals that exclude 1, indicating that the differences between sides
are significant. This finding makes sense, because we expect premature
Figure 7.2 Three-dimen-
sional CT reconstruction
of a child with premature
closure of the coronal
suture (superior view, with
anterior toward the top).
The fused coronal suture
is on the left side, where
the frontal bone appears
flattened.