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Figure 4.9. Scatter plot showing results of an EDMA comparison of the two forms
whose data are presented in Figure 4.8 . The Y-axis represents the value of the ele-
ments of the form difference matrix, while landmark numbers are shown along the
X-axis. The ratio value for the comparison of each linear distance is shown twice on the
graph, once for each landmark that is an endpoint for the linear distance. The values
for the comparison of a linear distance with itself (that value always being “1”) are not
entered on the graph. On the graph shown at the left we see all form difference ratios
for all linear distances. The column for landmark three suggests that large values are
associated with this landmark. On the graph shown at the right all ratios associated
with linear distances that have landmark 3 as an endpoint are graphed as closed
squares showing that the outlying values for each landmark map to the distance
between that landmark and landmark 3.
value corresponding to each landmark pair. For example, the value rep-
resenting the ratio for the landmark pair 3, 4 will be plotted once above
the “3” on the X-axis and again above the “4” on the X-axis.
A pattern is easily seen when looking at the scatter plot ( Figure
4.9a ). All points plotted in the column for landmark 3 are skewed
towards the extremes of the values on the Y-axis. When a different
marker (e.g., ) is used to represent those points that correspond to
linear distances that have landmark 3 as an endpoint ( Figure 4.9b ) ,
these linear distances stand out from all others.
Cole and Richtsmeier (1998) suggest the use of such plots for
exploring the influence of a particular landmark. The distribution of
the form difference matrix elements that correspond to a single land-
mark gives a visual impression of its influence. This approach could be
used as a complement to the “delete one” procedure just described, by
sequentially eliminating landmarks from the plot beginning with the
most influential. However, if this is done the investigator should be
 
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