Quality and Reliability Methods - SAS

282 Degradation Chapter 16
Model Specification
• An overlay plot of the Y, Response variable versus the Time variable. In this example, the plot is of
Current versus Hours. The Overlay plot red triangle menu has the Save Estimates option, which
creates a new data table containing the estimated slopes and intercepts for all units.
• The Model Specification outline. For more details, see “Model Specification” on page 282.
• The Residual Plot tab. There is a single residual plot with all the units overlaid, and a separate residual
plot for each unit. The Save Residuals option on the red triangle menu saves the residuals of the
current model to a new data table. The red-triangle menu has the following options:
– Save Residuals saves the residuals of the current model to a new data table.
– Jittering adds random noise to the points in the time direction. This is useful for visualizing the data
if there are a lot of points clustered together.
– Separate Groups adds space between the groups to visually separate the groups. This option
appears only when an X variable is specified on the platform launch window.
– Jittering Scale is used to change the magnitude of the jittering and group separation.
• The Inverse Prediction tab. For more details, see “Inverse Prediction” on page 290.
• The Prediction Graph tab. For more details, see “Prediction Graph” on page 292.
Model Specification
You can use the Model Specification outline to specify the model that you want to fit to the degradation
data. There are two types of Model Specifications:
Simple Linear Path is used to model linear degradation paths, or nonlinear paths that can be
transformed to linear. For details, see “Simple Linear Path” on page 282.
Nonlinear Path is used to model nonlinear degradation paths, especially those that cannot be
transformed to linear. For details, see “Nonlinear Path” on page 284.
To change between the two specifications, use the Degradation Path Style submenu from the platform red
triangle menu.
Simple Linear Path
To model linear degradation paths, select Degradation Path Style > Simple Linear Path from the platform
red triangle menu.
Use the Simple Linear Path Model specification to specify the form of the linear model that you want to fit
to the degradation path. You can model linear paths, or nonlinear paths that can be transformed to linear.
See Figure 16.4.