Quality and Reliability Methods - SAS

Chapter 7 Multivariate Control Charts 115
Platform Options
having the maximum test statistic value for the Change Point Detection plot. For the Gravel.jmp data, at
least one shift is apparent, with the change point occurring at observation 24 and the shift occurring
immediately following observation 24. See “Change Point Detection” on page 118 in this chapter for
technical details about shift changes.
A scatterplot matrix of the data, divided into two groups, is shown in Figure 7.9. This plot shows the shift in
the sample mean vector. The first 24 observations are identified as the first group; the remaining
observations are classified as the second group. The 95% prediction regions for the two groups have
approximately the same size, shape, and orientation, visually indicating that the sample covariance matrices
are similar.
The Scatterplot Matrix is created automatically when you select Change Point Detection from the
platform’s menu; however, you might need to slightly alter the axes in order to see the density ellipses for the
two groups, depending on your data. This is done by clicking and dragging the axes, as needed. For this
example, you can also create the plot shown in Figure 7.9 with the Gravel.jmp sample data table. Click the
red-triangle icon for Multivariate Control Chart and select Run Script.
Figure 7.9 Gravel.jmp Scatterplot Matrix
Note: The Change Point Detection method is designed to show a single shift in the data. Multiple shifts
can be detected by recursive application of this method.
Platform Options
The following options are available from the platform drop-down menu
T 2 Chart
shows or hides the T 2 chart.
T Square Partitioned enables you to specify the number of major principal components for T 2 .
Set Alpha Level
Show Covariance
sets the α-level used to calculate the control limit. The default is α=0.05.
shows or hides the covariance report.