A bubble plot is an effective multivariate data visualization.
Bubble plots allow up to five variables to be visualized simultaneously
with variables plotted on the x- and y-axes, bubble size and color
can represent two more variables, and animation allows a fifth variable
to be included. Animation is useful for time dependent variables.
Bubble plots can be created from the JMP
Graph menu.
Figure 9.12 Bubble Plot Dialog shows
the completed dialog needed to create a bubble plot with four variables
from the VHA data table. The change in backlog is shown on the y-axis
and the hospital location (city and state) appears on the x-axis.
The size of the bubbles indicates the magnitude of the backlog in
May 2016 and the color scale represents the size of the hospital as
measured by the number of in-patient beds.
The plot can be enhanced
by adding a reference line at 0 on the y-axis to clearly delineate
those hospitals whose backlog has increased and those whose backlog
has decreased. This can be done by right clicking over any of the
numbers on the y-axis scale and selecting Axis Settings. Type 0 into
the Value field in the Reference Lines portion of the dialog and click
Add. Note that a preview of the reference line appears to the right.
The bubble plot with the added reference line is shown in
Figure 9.14 Bubble Plot for VHA Appointment Backlogs with Reference Line.
In this plot we see
that the Fayetteville, NC facility has experienced a considerable
reduction in backlog and that in 2016 it has a relatively small backlog
of appointments over 31-60 days. Fayetteville has one of the smallest
in-patient capacities. Six of the larger facilities appear to have
had small changes in their backlogs relative to 2015. These facilities
are generally, although not exclusively, larger sized facilities.
Not surprisingly, large backlogs in 2016 are associated with increases
in backlog over the previous year as shown by the larger circles at
the top of the bubble plot.
In this visualization
we see that while the Fayetteville, NC facility appears to have improved
their backlog performance over the year, it has one of the lowest
patient satisfaction ratings. The two red-shaded bubbles are the
hospitals with the highest patient satisfaction but had large increases
in their backlog.