As a Director of AMP I get asked a multitude of questions, most are simple and somewhat repetitive. But I often find the diamond in the rough, a question that if resolved has the potential to advance reliability. I received an inquiry that had me puzzled; a hazards model originally developed for human health applied to reliability. This question is a challenge. I have my opinion but let’s see who can take a deep dive. Remember, it is not as simple as just as answer. Let’s stand in the inquiry and advance reliability.
Dear Mr. Smith,
I read the book “The Reliability Handbook” by John D. Campbell in which Mr. Campbell explains how to implement the Cox’s Proportional Hazards Model for condition monitoring analysis. I have been studying this model on my own, however literature references on this subject are scarce and not quite comprehensible.
I would be very grateful if you could give me some advice on the following questions:
1. What is the best method to estimate the covariate parameters vector γ? I have read literature indicating Cox’s partial likelihood method as the method of choice, however other authors mention multiple (linear) regression.
2. How do you estimate the baseline hazard? One of Cox PHM advantages is that covariate parameters γ are invariant to the baseline hazard, however from a time-to-failure perspective, it might be necessary to quantify it.
3. Is Cox PHM suitable for heterogeneous populations? I understand one should try to perform reliability analysis on homogeneous populations of equipment, however Cox PHM is widely used in biostatistics where populations are quite heterogeneous.
I would really appreciate if you could give me some advice on these questions and I look forward to hearing from you.
Now I would like to add some questions of my own.
1) Should you use the hazards model how would you apply the findings?
2) Could this provide the link to correlate risk profiles to renewal programs
3) Who has experience with this model and how did you apply it?
Jeff Smith, CRL-Bb