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A contingency table, as in the chi-squared test of independence, reveals if two sets of data or groups are independent or not. It does not reveal the strength of the dependence. The contingency coefficient is a non-parametric measure of the association for cross-classification data. [Read more…]
“The language we use matters.” Wayne Nelson
How we talk about reliability does matter. It sets expectations and influences decisions. We talk about reliability as it is important to our customers and our business. The successful operation of the equipment in a plant permits the production of products. The successful operation of the product satisfies the needs and expectations of our customers.
The chi-square ( $- \chi^2 -$) test provides a means to determine independence between two or more variables. In this case, it works for count data.
Contingency table or row and column (r x c) analysis are other common names for this analysis. It is useful when comparing results from different treatments or processes. [Read more…]
Years ago a client asked for help in reducing the amount of reliability testing they did for each project. They had a sense that some of the testing wasn’t useful. What they want to know was how to select the appropriate testing and be sure they wouldn’t miss anything important.
There are two basic approaches when addressing product reliability: Reactive or Proactive. Neither is right or wrong.
The reactive approach has the limitation of responding to failures that occur during prototyping, production and customer use.
The proactive approach focuses on preventing product design, assembly, and use issues before they have the opportunity to create a product failure.
Here’s an overview of a distribution-free approach commonly called the Kaplan-Meier (K-M) Product Limit Reliability Estimator.
There are no assumptions about underlying distributions. And, K-M works with datasets with or without censored data. We do need to know when failures or losses (items removed from the evaluation or test other than as a failure. Censored items). [Read more…]
Just opened registration for a CRE preparation course. http://fmsrel.com/1hW57Yt
Starting in August and running through September. All online.
A common expectation consumers have concerning products is that the product works. The product provides value by performing one or more functions. Also, implicit with this expectation is the product will function over some duration. A reliable product meets or exceeds this common expectation.
Every product has a finite duration of successful operation before failure occurs.
Recently I participated in an ASQ CRE focus group with a few of our peers. The ASQ facilitator prompted each of use to answer a few questions. Then she asked each of us to contribute to a “Start, Stop, Change” exercise focused on the CRE exam.
It appears ASQ is starting another round of reviews and possible updates to the CRE Body of Knowledge and exam process. That is good. [Read more…]
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…]