Quality and Reliability Methods - SAS

Chapter 18 Reliability Growth 343
Additional Examples of the Reliability Growth Platform
to 112 is not represented in the table). Since these make no contribution to the likelihood function, they are
not needed for estimation of model parameters.
However, to fit a Piecewise Weibull NHPP or Reinitialized Weibull NHPP model, it is important that the
start times for all phases be provided in the Time to Event or Timestamp columns.
Here, the three phases began at days 0 (Initial phase), 91 (Revised phase), and 200 (Final phase). There were
failures during the weeks that began the Initial and Revised phases. However, no failures were reported
between days 196 and 231. For this reason, an interval with beginning and ending days equal to 200 was
included in the table (row 23), reflecting 0 failures. This is necessary so that JMP knows the start time of the
Final phase.
The test was terminated at 385 days. This is an example of interval-censored failure times with time
terminated phases.
Note: The phase start times are required for proper display of the transition times for the Piecewise Weibull
NHPP model; they are required for estimation of the Reinitialized Weibull NHPP model. For
interval-censored data, the algorithm defines the beginning time for a phase as the start date recorded in the
row containing the first occurrence of that phase designation. In our example, if row 23 were not in the
table, the beginning time of the Final phase would be taken as 231.
1. Open the TurbineEngineDesign2.jmp sample data table.
2. Select Analyze > Reliability and Survival > Reliability Growth.
3. On the Time to Event Format tab, select the columns Interval Start and Interval End, and click Time to
Event.
4. Select Fixes and click Event Count.
5. Select Design Phase and click Phase.
6. Click OK.
7. From the red triangle menu at Reliability Growth, select Fit Model > Piecewise Weibull NHPP.
The Cumulative Events plot from the Observed Data report is shown in Figure 18.21. The vertical dashed
blue lines indicate the phase transition points. The first occurrence of Revised in the column Design Phase
is in row 14. So, the start of the Revised phase is taken to be the Interval Start value in row 14, namely, day
91. Similarly, the first occurrence of Final in the column Design Phase is in row 23. So, the start of the
Final phase is taken to be the Interval Start value in row 23, namely, day 200.