# Reliability Analysis

Blog posts and articles about reliability analysis methods used in Lean and Six Sigma quality improvement projects.

How many samples do you need to be “95% confident that at least 95%—or even 99%—of your product is good? The answer depends on the type of response variable you are using, categorical or continuous. The type of response will dictate whether you 'll use: Attribute Sampling: Determine the sample size for a categorical response that classifies each unit as Good or Bad (or, perhaps, In-spec or... Continue Reading
Reliability analysis is the perfect tool for calculating the proportion of items that you can expect to survive for a specified period of time under identical operating conditions. Light bulbs—or lamps—are a classic example. Want to calculate the number of light bulbs expected to fail within 1000 hours? Reliability analysis can help you answer this type of question. But to conduct the analysis... Continue Reading

### 7 Deadly Statistical Sins Even the Experts Make

Do you know how to avoid them?

I thought 3 posts would capture all the thoughts I had about B10 Life. That is, until this question appeared on the Minitab LinkedIn group: In case you missed it, my first post, How to Calculate B10 Life with Statistical Software, explains what B10 life is and how Minitab calculates this value. My second post, How to Calculate BX Life, Part 2, shows how to compute any BX life in Minitab. But... Continue Reading
Here is a scenario involving process capability that we’ve seen from time to time in Minitab's technical support department. I’m sharing the details in this post so that you’ll know where to look if you encounter a similar situation. You need to run a capability analysis. You generate the output using Minitab Statistical Software. When you look at the results, the Cpk is huge and the histogram in... Continue Reading
When I wrote How to Calculate B10 Life with Statistical Software, I promised a follow-up blog post that would describe how to compute any “BX” lifetime. In this post I’ll follow through on that promise, and in a third blog post in this series, I will explain why BX life is one of the best measures you can use in your reliability analysis. As a refresher, B10 life refers to the time at which 10% of... Continue Reading
Since it's the Halloween season, I want to share how a classic horror film helped me get a handle on an extremely useful statistical distribution.  The film is based on John W. Campbell's classic novella "Who Goes There?", but I first became  familiar with it from John Carpenter's 1982 film The Thing.   In the film, researchers in the Antarctic encounter a predatory alien with a truly frightening... Continue Reading
I recently fielded an interesting question about the probability and survival plots in Minitab Statistical Software's Reliability/Survival menus: Is there a one-to-one match between the confidence interval points on a probability plot and the confidence interval points on survival plot at a specific percentile? Now, this may seem like an easy question, given that the probabilities on a survival plot... Continue Reading
Over the last year or so I’ve heard a lot of people asking, “How can I calculate B10 life in Minitab?” Despite being a statistician and industrial engineer (mind you, one who has never been in the field like the customers asking this question) and having taken a reliability engineering course, I’d never heard of B10 life. So I did some research. The B10 life metric originated in the ball and roller... Continue Reading
These days, my memory isn't what it used to be. Besides that, my memory isn't what it used to be.  But my incurable case of CRS (Can't Remember Stuff) is not nearly as bad as that of the exponential distribution. When modelling failure data for reliability analysis, the exponential distribution is completely memoryless. It retains no record of the previous failure of an item. That might sound like a... Continue Reading
A couple of years ago, I wrote a blog post titled "What I Learned From Treating Childbirth as Failure" that conveniently ended up getting published the day before my daughter was born.  You should read it first, but to summarize it demonstrates how we can predict the odds of an event happening during certain time intervals even when the original data is highly censored. Since then, several people... Continue Reading
My main objective is to encourage greater use of statistical techniques in the service sector and present new ways to implement them. In a previous blog, I presented an approach you can use  to identify process steps that may be improved in the service sector (quartile analysis). In this post I'll show how nonparametric distribution analysis may be implemented in the service sector to analyze... Continue Reading
Over on the Indium Corporation's blog, Dr. Ron Lasky has been sharing some interesting ideas about using the Weibull distribution in electronics manufacturing. For instance, check out this discussion of how dramatically an early first-failure can affect an analysis of a part or component (in this case, an alloy used to solder components to a circuit board).  This got me thinking again about all the... Continue Reading
As we said in yesterday’s post, it’s been exciting for Minitab to be a supporter of the ASQ World Conference on Quality and Improvement taking place this week in Indianapolis. There have been many great sessions and an abundance of case studies shared that highlight how quality teams worldwide are improving the performance of their businesses. One session that generated a lot of interest from the... Continue Reading
Here at the lightsaber factory, we've completed several steps in doing a capability analysis: We made sure our data was collected and entered correctly in Minitab We identified the distribution of the data We made sure all of our assumptions checked out We’re getting close to our deadline, and it’s finally time to carry out our Capability Analysis and see if we are manufacturing our lightsabers to... Continue Reading
In college I had a friend who could go anywhere and fit right in. He'd have lunch with a group of professors, then play hacky-sack with the hippies in the park, and later that evening he'd hang out with the local bikers at the toughest bar in the city. Next day he'd play pickup football with the jocks before going to an all-night LAN party with his gamer pals. On an average weekend he might catch... Continue Reading
In industry, it may be presses and CNC machines. In education, it may be computers and microscopes. In retail, it may be the forklifts in the warehouse.  Regardless of your industry or the size of your business, in all likelihood you have one or more pieces of capital equipment that must be regularly maintained.  Typically these expensive pieces of equipment come with routine maintenance plans. ... Continue Reading
Despite the mountain of statistics backing the relative safety of air travel, I’m a nervous flyer. If a plane hits turbulence, I turn a light shade of olive green and start panting like a sick dog. When I look around the plane compartment, everyone else seems bored and unconcerned. Me? I’m clutching the arm rest, as 10,000 tiny ballerinas turn pirouettes in the pit of my stomach. It’s a visceral... Continue Reading