Teaching reliability occurs through textbooks, technical papers, peers, mentors, and courses. The many sources available tend to use MTBF as a primary vehicle to describe system reliability.
What has gone wrong with our education process?
MTBF Abounds in Books and Lectures
From tutorials by college professions at RAMS to numerous ‘reliability engineering’ text books the discussion equates reliability with MTBF. The way to measure or describe the reliability of something is MTTF for non-repairable or MTBF for repairable systems (like that bit of semantics matters).
Just use an average, it’s good enough.
A good text book does not mention MTBF, a great lecture avoids the use of MTBF. IMHO
When I confronted a professor on why a major portion of a tutorial on reliability statistics focused on MTBF, she said it was a great way to teach the concepts of distribution properties without worrying too much about the math. It was merely a mechanism to teach other concepts.
The lecture did not spend much time on applying those concepts to real problems. It did not explain the use of MTBF (and the exponential distribution) was a never to be used in the real world set of examples to focus on key concepts. It left, me and others in the room with the idea that MTBF was the way to describe reliability.
The same conversations with book authors.
MTBF is Easy
The ASQ CRE exam is rife with problems using MTBF (or MTTF). Why? – Because it is easy and quick to test calculations based on MTBF and the exponential distribution.
Sure it’s easy and not something we should be good at. Aren’t we supposed to be good at solving real problems, which are not easy? How about creating a certification exam that actually evaluates what we should know and do at work, not what is considered easy.
Students/Engineers Need to Understand MTBF
In more than one setting, as I rant on about the topic of abolishing MTBF, I encounter the rebuttal that students/engineers need to know about MTBF. If for no other reason than it is out there.
Sure, MTBF is on data sheets, test reports, parts count software outputs, etc. It is everywhere.
I agree students and engineers need to understand the folly that MTBF represents, the lack of information it contains, the inability to use it for any meaningful decision making. Instead students and engineers should learn to automatically insist on more information, data, evidence, all leading to an understanding of reliability (probably of success over time…).
When I hear someone ask for MTBF, I ask them what they really want to know. What they seek, when asking for MTBF, is never served or supported by knowing MTBF. We need to learn, and teach, reliability engineering to help each other ask better questions and solve real problems.
Stop This Vicious Cycle Now
If I use existing literature and teachings on reliability engineering to prepare a new book on the topic, I would likely feel compelled to include MTBF. I won’t other than to warn the reader to not use it at all.
You should do the same.
If in a class or tutorial where the instructor mentions MTBF, ask them when they will begin talking about something useful concerning reliability. Go ahead, you can say I urged you to ask.
If reading a book that drones on about MTBF testing and confidence intervals for time or failure truncated testing, send the author a note on when and under what conditions would this technique every be useful. Ask then to provide case studies and evidence that the underlying failure mechanisms involved are actually best fit by the exponential distribution. Ask them to justify spending more than one sentence of this expensive book on such drivel.
Go ahead, ask for rationale and justification. Ask for a better education.
If enough of use stand up and say, ‘hold on – when in the real world is the use of MTBF every useful?’, we just may get some professors and authors to provide meaningful content.
How have you challenged the use of MTBF? If you haven’t why not? What is holding you back?