Quality and Reliability Methods - SAS

Chapter 15 Recurrence Analysis 275
Fit Model
Homogeneous Poisson Process
I(t) = e γ te γ
C(t) =
where t is the age of the product.
Table 15.1 defines each model parameter as a scale parameter or a shape parameter.
Table 15.1 Scale and Shape Parameters
Model Scale Parameter Shape Parameter
Power NHPP θ β
Proportional Intensity PP γ δ
Loglinear NHPP γ δ
Homogeneous PP γ none
Note the following:
• For the Recurrence Model Specification window (Figure 15.12), if you include Scale Effects or Shape
Effects, the scale and shape parameters in Table 15.1 are modeled as functions of the effects. To fit the
models with constant scale and shape parameters, do not include any Scale Effects or Shape Effects.
• The Homogeneous Poisson Process is a special case compared to the other models. The Power NHPP
and the Proportional Intensity Poisson Process are equivalent for one-term models, but the Proportional
Intensity model seems to fit more reliably for complex models.
Click Run Model to fit the model and see the model report (Figure 15.13).
Figure 15.13 Model Report
The report has the following options on the red triangle menu:
Profiler
launches the Profiler showing the Intensity and Cumulative functions.
Effect Marginals evaluates the parameter functions for each level of the categorical effect, holding other
effects at neutral values. This helps you see how different the parameter functions are between groups.
This is available only when you specify categorical effects.