U-Matrix and Components Maps for Nine Allostatic Load Profiles: Map
A and Map B are graphic representations of the
cluster solution arrived at by the Self-Organizing Map (SOM) Neural
Net, referred to as the U-Matrix. In terms of the
information, they provide, Map A is a three-dimensional
(topographical) u-matrix: for it, the SOM adds hexagons to the original
15×11 map to allow for visual inspection of the degree of similarity
among neighboring map units; the dark blue areas indicate neighborhoods of cases
that are highly similar; in turn, bright yellow and red areas, as in the lower
right comer of the map, indicate highly defined cluster boundaries. Map
B is a two-dimensional version of Map A that
allows for visual inspection of how the SOM clustered the individual cases.
Cases on this version of the u-matrix (as well as Map A) were
labeled according to their k-means cluster membership (The nine cluster solution
shown in Table 2) to see if the SOM would
arrive at a similar solution. Map C is a graphic representation of the relative
influence that the seven factors (shown in Table
1) had on the SOM cluster solution. The SOM generates a mini-map for
the seven factors, each of which can be overlaid across maps A and B. Each of
these mini-maps can then be inspected visually to examine what its rates are
across the different neighborhoods (clusters of cases). Dark blue areas indicate
the lowest rates for a factor; and the bright red areas indicate the highest
rates for a factor. For example, looking at the mini-map for Factor 6
(Blood Sugar), its rates are extremely low across most of
the map, except for the lower right comer, which is where (looking at
Map A and Map B) the SOM placed Cluster
6.