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Tips and Techniques for Statistics and Quality Improvement

Blog posts and articles about using Minitab software in quality improvement projects, research, and more.

Can a 10-day forecast predict today's weather? I'm looking out the window at a slate-gray sky (again), and thinking about the last weather forecast I saw. That was a couple of days ago, but it called for sunny, warm weather. Not what I'm looking at now. On the other hand, it's the kind of weather that makes me glad to be inside analyzing data and doing statistics. Since the last weather forecast I... Continue Reading
A web of correlations can help or hurt you. Be the spider, not the fly. In recent posts, I’ve shown how confounding variables can flip your statistical analysis results on its head. And I’ve shown how random assignment in experiments can protect you from them in some cases. You might wonder: If you can’t randomize, is there another way to avoid the dangers of confounding variables? And, is there a... Continue Reading

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When you're conducting a Capability Analysis, do you know which statistic to look at?  We get a fair number of questions about this, so let's explore the question.  In the graph below, you’ll see that there are two categories for Capability Statistics, Potential and Overall:  The Potential (Within) Capability statistics(Cp, CPL…) are based off of the estimate for within standard deviation. Well,... Continue Reading
People like to say that seeing is believing, but the fact is that sometimes simply “seeing” isn’t enough. Whenever you’re making important decisions, like during a Lean Six Sigma project, it’s important to take a close look at the data. Because if you don’t, sometimes seeing is deceiving!Consider college basketball. Since 1990, the team ranked #1 in the AP preseason poll  has won the national... Continue Reading
My past several posts have detailed confounding variables, a problem you might encounter in research or quality improvement projects.To recap, confounding variables are correlated predictors. Leaving a confounding variable out of a statistical model can make an included predictor look falsely insignificant or falsely significant. In other words, they can totally flip your statistical analysis... Continue Reading
“I tried to think of the most harmless thing. Something I loved from my childhood. Something that could never, ever possibly destroy us. Mr. Stay Puft.” — Ray Venkman, Ghostbusters  It’s easy to understand why Ray from Ghostbusters, when trying to think of the safest thing he can, would think of something sweet to eat. Most folks like candy. Note that Ray, despite ostensibly having a PhD, did not... Continue Reading
I’d like to give you a chance to win some money. Tell me which of these games you’d rather play: Game 1: We flip a coin once. If it lands on tails, I’ll give you 100 bucks.Game 2: We flip a coin 10 times. If it lands on tails at least one time, I’ll give you 100 bucks. If you said “Doh” and picked Game 2, either you’re Homer Simpson or you already have a good intuitive understanding of an important... Continue Reading
The other day I needed to do some probability calculations without the usual technology on hand -- no computer, smart phone, or calculator. It was a great reminder of just how much I appreciate tools that make the work of analyzing data easier and faster. Anyone who's taken a statistics class that required you to do all calculations by hand recognizes the truth of a statement that someone posted... Continue Reading
Companies invest a great deal of time, effort, and money in Lean Six Sigma programs. So if you're doing a project, the expectations are probably high: companies that have made this investment expect good projects to challenge expectations, make processes better, and improve profitability. When you hear about projects that save companies like Motorola and General Electric millions of dollars, you... Continue Reading
In my last post, I detailed a study where the regression analysis seemed to show that higher calcium intake was associated with reduced injuries among our subjects. I had taken the data we collected for our main study and tried to use it to see if there were patterns amongst those who experienced the knee pain.A post hoc analysis like this can often give you good results but it can lead you... Continue Reading
In my last post, I discussed what the "Number of Distinct Categories" means in gage R&R output . Another common question with Gage Crossed is what table to look at when assessing your measurement system.  By default, Minitab gives a %Contribution table and %Study Variation table. Which one should you use when assessing where the variation is mostly coming from? Well, you could use either of them. ... Continue Reading
    "I gazed--and gazed--but little thought What wealth the show to me had brought: For oft, when on my couch I lie In vacant or in pensive mood, They flash upon that inward eye Which is the bliss of solitude; And then my heart with pleasure fills, And dances with the daffodils." — William Wordsworth The ending of Wordsworth’s poem is about pleasant memories, the kind that I want you to have of... Continue Reading
I’m lucky to be in a marriage where arguing is an unlikely occurrence, but I've found that common Lean Six Sigma tactics, such as 5-Why Analysis and Fishbone diagrams, can come in handy when I’m trying to solve minor disagreements with my husband.A 5-Why Analysis was developed by Toyota to solve defects in their vehicle process lines. The technique can help you diagnose the root cause of really... Continue Reading
In my last blog post, I tried to make a regression model to predict fantasy football scores for the upcoming NFL season. However, my R-Squared value (R-Sq) was only 61%. Now I'm going to break the data up by position to try and create a better model. I used the same data set as before, which means each player had played three full seasons with the same team. I ran Minitab’s regression analysis on... Continue Reading
So I’m standing at my desk last Tuesday, when my legs suddenly turn to Jell-O. Then I notice the overhead lights gently waving. Soon folks are popping out of their offices with quizzical, sometimes queasy expressions. A few phone calls and Internet searches confirm that we have just experienced a very rare, East Coast earthquake. One centered in Virginia but felt from Georgia to Maine. Wow.We were... Continue Reading
I’ve had the opportunity to talk to several quality improvement professionals from companies across many different industries, and I’ve heard about the common challenges practitioners face when they’re completing quality improvement projects. Here's a brief summary:Where do I start?A challenge faced by quality practitioners, especially newer Green Belts, is the breadth of available quality tools... Continue Reading
Most Lean Six Sigma projects use data analysis to examine and reduce the prevalence of defects in a product or service. Experienced quality practitioners know that defects can sometimes feel abstract when you analyze them, until you’re the customer who experiences them firsthand.   On my first trip to Rome, my luggage never showed up in the terminal.So instead of gazing in awe at the Sistine... Continue Reading
For those of you who have travelled to the UK before, it will come as no surprise that our fuel costs are amongst the highest in Europe. It appears that driving a car could soon become a luxury at this rate.Unfortunately, most of us here at Minitab Ltd. are reliant on our cars to be able to make it to the office every day. So, unless we are able to relocate closer to the office (which may not be... Continue Reading
Your Lean Six Sigma project resulted in tremendous process improvement. It's time to share the results. To help people understand your data quickly and clearly -- especially if they don’t know statistics -- you need graphs.Statistical software lets us use a wide array of graphs to display data, depending on what we want to convey. So why restrict yourself to pie or bar charts, when there are many... Continue Reading
Hi, I’m Greg Fox, a writer in the Information Development department here at Minitab. Have you ever clicked “Help” in Minitab and been awestruck by the wealth of timely and truly helpful content suddenly revealed before your very eyes? I hope so, because I write that stuff. Well, me and several other very smart and dedicated folks. We work hard to provide you with the documentation that you need... Continue Reading