Quality and Reliability Methods - SAS

292 Degradation Chapter 16
Prediction Graph
Set Censoring Time
is used to set the censoring time.
Use Interpolation through Data uses linear interpolation between points (instead of the fitted model) to
predict when a unit crosses the spec limit. The behavior depends on whether a unit has observations
exceeding the spec limit as follows:
– If a unit has observations exceeding the spec limit, the inverse prediction is the linear interpolation
between the observations that surround the spec limit.
– If a unit does not have observations exceeding the spec limit, the inverse prediction is censored and
has a value equal to the maximum observed time for that unit.
Inverse Prediction Interval is used to show confidence or prediction intervals for the pseudo failure
times on the Inverse Prediction plot. When intervals are enabled, the intervals are also included in the
data table that is created when using the Save Crossing Time option.
Inverse Prediction Alpha
Inverse Prediction Side
is used to specify the alpha level used for the intervals.
is used to specify one or two sided intervals.
Prediction Graph
Use the Prediction Graph tab to predict the Y variable for a specified Time value. Figure 16.16 shows the
Prediction Plot tab.
Figure 16.16 Prediction Plot Tab
For the GaAs Laser example, no data was collected after 4000 hours. If you want to predict the percent
increase in operating current after 5000 hours, enter 5000 and click Go. A plot is produced showing the
estimated percent decrease after 5000 hours for all the units. See Figure 16.17.