Category Archives: MTBF

Mean Time Between Failures or MTBF is a common metric for reliability and is often misused or misunderstood.

MTBF Use May Reduce Product Reliability

Is MTBF Preventing Your Product From Being Reliable?

MTBF is not reliability. Attaining a specific MTBF does not mean your product is reliable. MTBF use may be the culprit.

Therefore, working to achieve a MTBF value may actually be preventing you from creating a product that mets your customer’s reliability performance expectations.

Actively working to achieve MTBF using the common tools around MTBF may be taking you and your team down the wrong rabbit hole. You may be working to reduce the reliability of your products rather than improving them.

Let’s take a look at a couple of ways the pursuit of MTBF is harmful to your product’s reliability potential and contrary to your customer’s expectations. Continue reading MTBF Use May Reduce Product Reliability

How Did Reliabilty Become Confused with MTBF?

When Asking for Reliability Information Do You Ask for MTBF?

Our customers, suppliers, and peers seem to confuse reliability information with MTBF. Why is that?

Is it a convenient shorthand? Maybe I’m the one confused, may those asking or expecting MTBF really want to use an inverse of a failure rate. Maybe they are not interested in reliability.

MTBF is in military standards. It is in textbooks and journals and component data sheets. MTBF is prevalent.

If one wants to use an inverse simple average to represent the information desired, maybe I have been asking for the wrong information. Given the number of references and formulas using MTBF, from availability to spares stocking, maybe asking for MTBF is because it is necessary for all these other uses. Continue reading How Did Reliabilty Become Confused with MTBF?

The Business of Providing MTBF

Vintage advertisement of overhead craneWhat Price Providing MTBF?

If your livelihood consists of providing MTBF upon request, what good is your service?

Sure you earn some money, yet did the customer receive value in the transaction? As you know, or should know, MTBF is so commonly misunderstood that it is likely the customer confused what they want, reliability, with MTBF. Providing them MTBF does not answer their question.

Worse the customer thinks they got something of value and blithely heads off with rather meaningless information.

My contention is by providing MTBF because customer’s request it is wrong. We know better. Those performing predictions, doing data analysis, and other reliability engineering work know that MTBF is a faulty and rather meaningless metric often confused with reliability, R(t). (probability of success over a duration). Continue reading The Business of Providing MTBF

A Couple of Questions for You Concerning MTBF

Let me ask you something concerning MTBF

Do make compromises around gathering and analyzing data since you only need to report MTBF?

Do you use MTBF (exponential distribution) based test planning when you know the product has a non-constant hazard rate?

These questions came up this week via email looking for advice when directed to ignore the actual situation and just do what the customer wants.

I’m traveling this week, rather jet-lagged today, so going to keep this one short.

How would you answer these questions? What advice would you give someone using exponential based reporting, test planning, or data analysis approaches knowing the customer expects that process yet the data and your experience suggest you should use another method  (Weibull or MCF, for example)?

Please add you comments below and let’s prepare a list of what one should say or use to respond to such actions.


How to Judge a Reliability Book

How Do You Judge a Reliability Book?

By it’s cover no doubt. The title and cover are important, this is true. When you judge a reliability book we often first see and evaluate the cover.

The author? Do you buy the book based on who wrote or edited it?

Do you have a quick scan or check for key features before you add the book to your library? I’m curious how you select a book to use a reference for your work. The books we read and use for work shape our work, thus it’s important to have the right works at our disposal. Continue reading How to Judge a Reliability Book

High MTBF with Low Reliability

Can You Have a High MTBF and Low Reliability?

As regular readers know, MTBF by itself is misleading. When representing actual data it can be deceptive as well. Just because you have a high MTBF value doesn’t mean it is reliable.

In a previous article, 10 Reasons to Avoid MTBF, I mentioned that it is possible to have a relatively high MTBF value when the actual reliability is low. Ashley sent me the following note:

Hi Fred, i love reading your articles they are very informative. I have a question about something you said in a comment which i am hoping you will be able to clarify for me. You said products with higher MTBF can actually be less reliable than products with a lower MTBF

I have tried to find information on how this is possible online, and tried to do the maths myself to make this happen but i have to admit i am struggling.

No worries, Ashley, let’s work out an example to illustrate what I meant. Continue reading High MTBF with Low Reliability

10 Reasons to Avoid MTBF

“Why do you avoid MTBF?”

I got this question the other day. The person knew about the NoMTBF campaign. They didn’t quite understand why it was a big deal, especially for me, to avoid MTBF.

The tiff between MTBF and myself is not personal. The metric has not been a part of my work or caused any significant problems for me personally.

It has caused problems that have caused problems for my enjoyment of products and systems though. It has lead to poor decisions by many organizations that create items I and you use on a regular basis.

We can do better than to settle with the use of MTBF in our own work or in the work of those around us. Here are 10 reasons I recommend you avoid using MTBF.

Continue reading 10 Reasons to Avoid MTBF

REVIEW Analyzing Repairable System Failures Data

REVIEW: Analyzing Repairable System Failures Data

Recently, Ziad let me know he published an article titled Analyzing Repairable System Failures Data in the April-May 2017 issue of Uptime magazine (subscription required). He suggested I’d be interested in the article since it provides a way to analyze repairable system data without using MTBF. He was right.

The article is a short description and tutorial on using mean cumulative plotting and function (MCF). While the article recommends staying away from using MTBF, it could be a bit of a stronger message. The article does provide a very nice worked out example illustrating the use of a mean cumulative plot. Continue reading REVIEW Analyzing Repairable System Failures Data

We’ll Meet Your Reliability But Not Your Spec

A Problem With MTBF

(Physics gets in the way!)

A Guest Post by Kevin Walker

I had an interesting case study a couple weeks ago, where “I’m giving you what you want, not what you asked for “ when the requirement as usual was a blanket MTBF, but the product design elements clearly indicated wearout could / would be a factor. — Kevin

Continue reading We’ll Meet Your Reliability But Not Your Spec

The Challenges in Reliability Engineering

What are the Other Challenges in Reliability

Creating a product or system that lasts as long as expected, or longer, is a challenge.

It’s a common challenge that reliability engineering and entire engineering team face on a regular basis. It’s also not our only challenge.

We face and solve a myriad of technical, political, and engineering challenges. Some of our challenges are born and carried forward by our own industry. We have tools suitable for a given purpose altered to ‘fit’ another situation (inappropriately and creating misleading results). We have terms that we, and our peers, struggle to understand.

Sometimes, we, as reliability engineers have set up challenges that thwart our best efforts to make progress.

Let’s examine a few of the self made challenges and discuss ways to overcome these obstacles permitting us to tackle the real hurdles in our path. Continue reading The Challenges in Reliability Engineering

Why Do a Parts Count Prediction?

Why Would You Do a Parts Count Prediction?

Is there any useful result from a parts count prediction?

In most cases that I’ve seen parts count predictions used they are absolutely worthless. Worse, is the folks receiving the results believe they are accurate estimates of reliability performance (or at least use the results as such).

In my opinion, the range of parts count prediction methods and databases harm the field of reliability engineering.

We need to call out the poor results, promote better practices, and stop the vapid use of such a poorly understood tool. Continue reading Why Do a Parts Count Prediction?

MTBF and Mean of Wearout Data

MTBF is Just the Mean, Right?

A conversation the other day involved how or why someone would use the mean of a set of data described by a Weibull distribution.

The Weibull distribution is great at describing a dataset that has a decreasing or increasing hazard rate over time. Using the distribution we also do not need to determine the MTBF (which is not all that useful, of course).

Walking up the stairs today, I wondered if the arithmetic mean of the time to failure data, commonly used to estimate MTBF, is the same as the mean of the Weibull distribution. Doesn’t everyone think about such things?

Doesn’t everyone think about such things? So, I thought, I’d check. Set up some data with an increasing failure rate, and calculate the arithmetic mean and the Weibull distribution mean. Continue reading MTBF and Mean of Wearout Data

Is Using MTBF Habit Forming?

With Enough Reinforcement, MTBF Use Becomes a Habit

A habit you should examine and stop.

At first, I wondered if MTBF use was addictive, yet thought that comparison would belittle the very serious issues of those with addictive behaviors. Using MTBF does not generally cause a person harm, while poor decision based on it might harm the organization.

I find those that regularly employ MTBF do so without thinking about it too much. If someone mentions reliability, they think MTBF. Automatically.

Habits help us reduce cognitive load and make our life simpler. For example, do you need to focus on how to put on your shoes every morning? I’m personally happy my habit skills allow me to remember how to drive safely without the intense focus required the first time I got behind the wheel.

Let’s examine how to tell if someone has the Habit of MTBF use and what you can do about it. Continue reading Is Using MTBF Habit Forming?

Learn Reliability, Not Just MTBF

MTBF is a Starting Point, Only

MTBF is not meant to be used for anything other than teaching someone new to reliability how the various functions and tasks work.

Using MTBF in the real world is an oversimplification to the point of being less then useful. Possibly even harmful.

You see MTBF is books, articles, and papers, often with the caveat of the assumption to simplify the math to illustrate the process or concept. Hence, does not apply for actual use. Continue reading Learn Reliability, Not Just MTBF