Quality and Reliability Methods - SAS

Chapter 18 Reliability Growth 333
Fit Model Options
Show Profilers
Three profilers are displayed, showing estimated MTBF, Failure Intensity, and Cumulative Events
(Figure 18.11). These profilers do not use logarithmic scaling. By dragging the red vertical dashed line in
any profiler, you can explore model estimates at various time points; the value of the selected time point is
shown in red beneath the plot. Also, you can set the time axis to a specific value by pressing the CTRL key
while you click in the plot. A blue vertical dashed line denotes the time point of the last observed failure.
The profilers also display 95% confidence bands for the estimated quantities. For the specified time setting,
the estimated quantity (in red) and 95% confidence limits (in black) are shown to the left of the profiler. For
further details, see “Profilers” on page 347.
Note that you can link these profilers by selecting Factor Settings > Link Profilers from any of the profiler
red triangle menus. For further details about the use and interpretation of profilers, see Modeling and
Multivariate Methods, Fitting Standard Least Squares Models, Factor Profiling, The Profiler.
Figure 18.11 Profilers
Achieved MTBF
A confidence interval for the MTBF at the point when testing concludes is often of interest. For uncensored
failure time data, this report gives an estimate of the Achieved MTBF and a 95% confidence interval for the
Achieved MTBF. You can specify a 100*(1-α)% confidence interval by entering a value for Alpha. The
report is shown in Figure 18.12. For censored data, only the estimated MTBF at test termination is
reported.