Quality and Reliability Methods - SAS

Chapter 16 Degradation 291
Inverse Prediction
Figure 16.14 Inverse Prediction Tab
Enter either the Lower or Upper Spec Limit. Generally, if your Y variable decreases over time, then enter a
Lower Spec Limit. If the Y variable increases over time, then enter an Upper Spec Limit.
For the GaAs Laser example, enter 10 for the Upper Spec Limit and click Go. A plot is produced showing
the estimated times until the units reach a 10% increase in operating current. See Figure 16.15.
Figure 16.15 Inverse Prediction Plot
The Inverse Prediction red triangle menu has the following options:
Save Crossing Time saves the pseudo failure times to a new data table. The table contains a Life
Distribution or Fit Life by X script that can be used to fit a distribution to the pseudo failure times.
When one of the Inverse Prediction Interval options is enabled, the table also includes the intervals.
Set Upper Spec Limit
Set Lower Spec Limit
is used to set the upper spec limit.
is used to set the lower spec limit.