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”
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?”
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”
How Does One Change an Industry
Jobs at Apple has done it. You can, too.
Change an industry. The advent of iTunes and iPods forever changed how the world buys and listens to music.
While Jobs had the resources of Apple to help make the change happen. It still started as an idea (may or may not have been Jobs’ idea, I don’t know). It grew and created enough momentum to effect a change across an entire industry.
Change is hard.
If you have tried to help your team move in a new direction or consider the reliability risks present in the current design, then you know change is difficult to make happen. You most likely have been successful a few times, and not a few also. I know I’ve crashed into the rocky spit more often than I can count. Continue reading “How Does One Change an Industry”
5 Ways Your Reliability Metrics and Fooling You
We measure results. We measure profit, shipments, and reliability.
The measures or metrics help us determine if we’re meeting out goals if something bad or good is happening, if we need to alter our course.
We rely on metrics to guide our business decisions.
Sometimes, our metrics obscure, confuse or distort the very signals we’re trying to comprehend.
Here are five metric based mistakes I’ve seen in various organizations. Being aware of the limitations or faults with these examples may help you improve the metrics you use on a day to day basis. I don’t always have a better option for your particular situation, yet using a metric that helps you make poor decisions, generally isn’t acceptable.
If you know of a better way to employ similar measures, please add your thoughts to the comments section below. Continue reading “5 Ways Your Reliability Metrics and Fooling You”
The Dirge of the MTBF Bias
We use our biases every day to make choices.
We select the beige sweater because we have a color bias concerning our sweaters.
Many of our biases help us quickly make decisions. We rely on biases to move through the day. Many of our biases are under the surface, unconsciously guiding our daily decisions. Mostly, biases are good or at least inconsequential.
The problem is the bias that shields us from achieving our goals. Continue reading “The Dirge of the MTBF Bias”
When Do Failures Count?
One technique to calculate a product’s MTBF is to count the number of failures and divide into the tally of operating time.
You already know, kind reader, that using MTBF has its own perils, yet it is done. We do not have to look very far to see someone estimating or calculating MTBF, as if it was a useful representation of reliability… alas, I digress.
Counting failures would appear to be an easy task. It apparently is not. Continue reading “When Do Failures Count?”
Sample Size and Duration and MTBF
If you have been a reliability engineer for a week or more, or worked with a reliability engineer for a day or more, someone asked about testing planning. The conversation may have started with “how many samples and how long will the test take?”
You have heard the sample size question.
Continue reading “Sample Size and Duration and MTBF”
Learn to Notice MTBF Everyday
Did you notice the speed limit signs in your neighborhood today?
If like me, you went about your commute or regular travels relatively blind. You watched for the neighbor’s dog that jumped into the road last week, yet didn’t register seeing the speed limit sign.
It’s a cognitive burden to notice the mundane or known. Continue reading “Learn to Notice MTBF Everyday”
The 3 Best Reasons to Use MTBF
This may seem an odd article for the NoMTBF site. Stay with me for a moment longer.
Over the years of speaking out on the perils of MTBF, there has been some push back. A few defend using MTBF. Here are three of the most common (maybe not exactly the best, per se) reasons to use MTBF. Continue reading “The 3 Best Reasons to Use MTBF”
Illuminating MTBF’s Lack of Information
Here’s a simple illustration of how MTBF oversimplifies data concealing essential information.
By convention, we tend to use MTBF for repairable data. That is fine.
You may also be aware of my dislike for the use of MTBF, for many different reasons. If you find yourself suggesting your organization, customer, industry or whomever to stop using MTBF, you may want to use this simple example to illustrate the ‘value’ of MTBF. Continue reading “Illuminating MTBF’s Lack of Information”
A Quick MTBF Search Reveals Distressing Results
I was preparing to write this article and wondered how many search hits would appear for MTBF? So, opened Google and did an MTBF search. It is a common if misunderstood, acronym.
Beyond the 5,200,000 Google search results, it was the first page results that got me thinking. Keep in mind that Google often serves up a combination of what it thinks you are seeking and which sites have been useful for others.
Let’s break down what you find when you do an MTBF search. Continue reading “MTBF Search Result Sadness”
4 Questions to Ask When Confronted with MTBF
MTBF comes up a bit too often. When it does I have found rolling my eyes and arguing against using MTBF is not very effective.
So, what should a knowing reliability professional do instead?
Let’s explore four questions that you can ask that may help others find the value in no longer talking about MTBF. Continue reading “4 Questions to Ask When Confronted with MTBF”
Replace After MTTF Time To Avoid Failures – Right?
Received a short question last week. The person writing seems to already know the answer, yet asked:
If we replace an item after a duration equal to the MTTF value, we would avoid failures, right?
Well, no, most likely not, was my response. What is your response? How would you answer this question? Continue reading “Replace After MTTF Time To Avoid Failures – Right?”
Yet Another Confused MTBF Definition
Just when I thought we had experienced every possible MTBF definition confusion, here’s another.
This one is courtesy the thread concerning the impact to reliability when adding redundancy to a system. Continue reading “Yet Another Confused MTBF Definition”