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This is a non-parametric test to compare ranked data from three or more groups or treatments. The basic idea is to compare the mean value of the rank values and test if the samples could are from the same distribution or if at least one is not.
The null hypothesis is the data from each group would receive about the same mean rank score. We are comparing rank values, not the actual values. [Read more…]
In Katmandu, I visited a small pottery factory. There was a young man sitting at a potting wheel making candle stands. He didn’t measure anything and I doubt anyone did.
Based on experience and just looking at a finished item, he could tell if it was acceptable or not. That was good enough.
Reliability coaching is one-to-one or small team discussions lead by an experienced reliability engineer (me) focused on achieving an agreed upon goal for the coaching program.
When I first started working in a factory as a shift supervisor, it seemed there was some type of formal training nearly every month. And we were expected to attend a conference once a year. Little did I know that was a great time to start working in industry. We enjoyed a lot of great training.
Later in my career and as the economy changed budgets for training slowly declined. Travel budgets also slipped away. I don’t have hard numbers, yet I suspect there is less company-sponsored professional development than 20 years ago.
As an engineering working in the reliability field, how do you keep up and learn what you need to know to accomplish your work? [Read more…]
It always seems there are more red lights when I’m running late.
This comment and others similar to it caught my attention lately. Is it just Murphy’s Law or something else?
There is an element of luck or chance in many events during our daily lives. The same is true when producing products and the resulting reliability. A lot has to go right for the product to work for the customer.
When something isn’t going as expected, we have a comparison that gains attention. If the lights are red more often, in theory, when I’m running late, maybe the lights are not turning red more often, it’s just that we notice.
For product development, it’s noticing the items that are going well and failing that matter. As reliability professionals, we need to continue to practice being aware of what is expected and what actually happens. [Read more…]
This non-parametric analysis tool provides a way to compare two sets of ordinal data (data that can be rank ordered in a meaningful manner). The result, rs, is a measure of the association between two datasets.
You may want to know if two reviewers have similar ratings for movies, or if two assessment techniques provide similar results. [Read more…]
Let’s say we have data that is only rank order from two or more evaluators (people, algorithms, etc.) and we want to determine if the evaluators agree or not.
The agreement here meaning the results from one person or another are in agreement, or they are concordant. This is typically done with this non-parametric method for 3 or more evaluators. For a comparison of two evaluators consider using Cohen’s Kappa or Spearman’s correlation coefficient as they are more appropriate. [Read more…]
Reliability engineers learn basic tools and techniques most often from others with that knowledge. During our careers, we also continue to learn and often find ourselves teaching. Even when mentoring we find ourselves learning. Being a deliberate and active student and teacher is a great way to remain inquisitive and helpful.
Formal education will make you a living; self-education will make you a fortune. [1]
Learning never stops. [Read more…]
Detecting a change or difference is often the aim of an experiment or set of measurements. We want to learn which vendor, process, or design provides a better result.
When we use a sample to estimate a statistic for a population we take the risk that the sample provides values that are not representative of the population. For example, if we use a professional basketball team to sample men’s height. We may conclude that the height of men in the general population is taller than the true population value. [Read more…]
Value is:
the regard that something is held to deserve; the importance, worth,
or usefulness of something. [1]
As a reliability engineer, we work across the organization to bring a reliable product to market. The value of meeting the customer’s reliability expectations results in customer satisfactions, increased sales, and in some cases premium pricing.
We want a reliable product.
The U test permits the comparison of two samples to determine if they came from the same population or not. This non-parametric test can use ordinal data, meaning it is in some rank order without containing information about relative distances between ranks. [Read more…]
Many elements help make a reliability engineer successful.Two such elements are knowing the right people to get the job done and generally being a positive and enjoyable person to be around.
A test to determine if the homogeneous Poisson model (HPP) is applicable given the data from an individual system is subject to the non-homogeneous Poisson model (NHPP).
This is an alternative test to using the Kendall-Mann Reverse Arrangement Test. [Read more…]
My dictionary says that talented is “having a natural aptitude or skill for something.”
We learn reliability engineering and those who understand the range of tools and techniques useful for a given situation would be considered talented.
Everything is not solved by running a highly accelerated life test (HALT) or only conducting detailed failure analysis. Knowing when and why to apply a particular tool and using the tool effectively (i.e., when to use a Weibull distribution to model lifetime data and how to use the information to make decisions) are critical. [Read more…]
When something fails, what should we do?
A natural question when something fails is
Why did it fail?
The answer is not always obvious or easy to sort out.
One of my favorite examples was on a circuit board that had a small burn mark where a component exploded off the board. The customer didn’t notice that missing part, our engineering team did that. [Read more…]
