When it comes to creating control charts, it's generally good to collect data in subgroups, if possible. But sometimes gathering subgroups of measurements isn't an option. Measurements may be too expensive. Production volume may be too low. Products may have a long cycle time.

In many of those cases, you can use an I-MR chart. Like all control charts, the I-MR chart has three main uses: 

• Monitoring the stability of a process.
  Even very stable processes have some variation, and when you try to fix minor fluctuations in a process you can actually cause instability. An I-MR chart can alert you to...

The DMAIC methodology for completing quality improvement projects divides project work into five phases: define, measure, analyze, improve, and control. It’s also probably the most well-known and most used project methodology for projects that focus on improving an existing process. (Many other methodologies exist, such as DMADV, which focuses on using quality improvement techniques to create a new product of process design.)

Franciscan Hospital for Children, a hospital in Brighton, Mass., that specializes in the care of children with special health care needs, recently completed a project...

My family moved to Los Angeles in 1987, just as the Los Angeles Lakers were in the midst of winning back-to-back championships. While I don’t consider myself a huge basketball fan, the NBA finals always hold some interest for me. If you get to watch James Worthy, Michael Cooper, Byron Scott, A.C. Green, Magic Johnson, and Kareem Abdul-Jabbar win championships, it sticks with you.

So now that the Spurs and Heat are competing for the 2013 edition of the NBA championships, I get a little drawn in by the excitement. One of the interesting occurrences from this year’s finals is that the two teams...

Multiple regression can be a beguiling, temptation-filled analysis. It’s so easy to add more variables as you think of them, or just because the data are handy. Some of the predictors will be significant. Perhaps there is a relationship, or is it just by chance? You can add higher-order polynomials to bend and twist that fitted line as you like, but are you fitting real patterns or just connecting the dots? All the while, the R-squared (R2) value increases, teasing you, and egging you on to add more variables!

Previously, I showed how R-squared can be misleading when you assess the...

Have you heard about the Tennessee man who has 22 children to 17 different women? He was interviewed the other day, and when asked how he supports all his kids he was quoted as saying:

"I'm just hoping one day I'll get lucky and might scratch off the numbers or something. I play the hell out of the Tennessee lottery."

Well, what would it look like if a person really did play "the hell" out of the lottery? Say you spent a year buying one $10 scratch-off ticket each day. How likely would you be to come out ahead? And for that matter, how would the lottery compare to making a $10 sports bet or a...

I previously started looking into which method of gambling was your best bet: a NFL bet, a number on a roulette wheel, or a scratch-off lottery ticket. After calculating the expect value for each one, I found out that the NFL bet and roulette bet were similar, as each had an expected value close to -$0.50 on a $10 bet. The scratch-off ticket was much worse, having an expected value of -$2.78.

But I want see how each of these games could play out in real life. After all, it is possible for people to come out ahead playing each game. So I planned to take 300 people, split them into 3 groups (one...

A t-test is one of the most frequently used procedures in statistics.

But even people who frequently use t-tests often don’t know exactly what happens when their data are wheeled away and operated upon behind the curtain using statistical software like Minitab.

It’s worth taking a quick peek behind that curtain.

Because if you know how a t-test works, you can understand what your results really mean. You can also better grasp why your study did (or didn’t) achieve “statistical significance.”

In fact, if you’ve ever tried to communicate with a distracted teenager, you already have experience with...

New Jersey Gov. Chris Christie is currently in a battle with sports leagues over the issue of allowing sports betting at casinos in Atlantic City and horse racing tracks across the state. If he wins and sports betting becomes legal in New Jersey, it will open the door for other states to follow suit. It appears there is a long way to go before this form of gambling spreads across the country.

But is sports betting really so much worse than casinos (which are legal in just under half of all U.S. states) or the lottery (which is legal in almost every U.S. state)?  For the purposes of this...

Yesterday I wrote about how paleontologist Zhijie Jack Tseng used 3D surface plots created in Minitab Statistical Software to look at how the skulls of hyenas and some extinct dogs with similar dining habits fit into a spectrum of possible skull forms that had been created with 3D modelling techniques.

What's interesting about this from a data analysis perspective is how Tseng took tools commonly used in quality improvement and engineering and applied them to his research into evolutionary morphology.

We used Tseng's data to demonstrate how to create and explore 3D surface plots yesterday, so...

A while back my colleague Jim Frost wrote about applying statistics to decisions typically left to expert judgment; I was reminded of his post this week when I came across a new research study that takes a statistical technique commonly used in one discipline, and applies it in a new way. 

The study, by paleontologist Zhijie Jack Tseng, looked at how the skulls of bone-cracking carnivores--modern-day hyenas--evolved. They may look like dogs, but hyenas in fact are more closely related to cats. However, some extinct dog species had skulls much like a hyena's. 

Tseng analyzed data from 3D...

I recently had the opportunity to talk with Ken Jones, professor of operations and supply chain management at Indiana State University, about a business process improvement course he teaches at the university. The course covers a variety of Lean Six Sigma tools and techniques and gives students the opportunity to team with local businesses to complete real quality improvement projects. Upon successful completion of the class, students even become certified green belts.

One item we talked about was how valuable the experiential component of the projects can be for students, especially...

When you learned statistics, most of what you learned was centered around the Normal distribution.  Maybe you became close friends and you later found out his birth name was Gaussian, but either way you probably just call him Normal.

You might know Normal’s a pretty popular guy with plenty of relationships with other distributions.  There are some obvious connections, like how eNormal is Lognormal, but I thought I’d share some less obvious ones. 

You probably already know that by subtracting his mean and dividing by his standard deviation you get Standard Normal.

What if you squared Standard...

by Alex Orlov, guest blogger

While it has been called the "million-dollar methodology" for the significant investment sometimes required to deliver results, Six Sigma has a wealth of practices that can be adapted to small and medium industries, home businesses and even personal finances. 

Organizations have used Six Sigma as a reliable part of the quality improvement process since 1986. And while a large Six Sigma project could cost anything from $1,000 to $1 million in work-hours and other resources, the results of such projects often far outweigh the investment. In addition to the direct...

After you have fit a linear model using regression analysis, ANOVA, or design of experiments (DOE), you need to determine how well the model fits the data. To help you out, Minitab statistical software presents a variety of goodness-of-fit statistics. In this post, we’ll explore the R-squared (R2 ) statistic, some of its limitations, and uncover some surprises along the way. For instance, low R-squared values are not always bad and high R-squared values are not always good!

What Is Goodness-of-Fit for a Linear Model?

Linear regression...

Previously I wrote about using a decision matrix to help make a decision. Matrices are nice tools for collecting your thoughts and visualizing a decision. But complex decisions could involve collecting and synthesizing input from a number of different people.

Quality Companion (Minitab's process improvement software) uses ballots to let team members record their input to a decision matrix. If you’ve already made the matrix, setting up the ballot is easy. The ballot simplifies data collection and organization, even among team members who are dispersed in space and time. You can follow along in...

There's been a really interesting conversation about correlation and causation going on in the LinkedIn Statistics and Analytics Consultants group. 

This is a group with a pretty advanced appreciation of statistical nuances and data analysis, and they've been focusing on how the understanding of causation and correlation can be very field-dependent. For instance, evidence supporting causation might be very different if we're looking at data from a clinical trial conducted under controlled conditions as opposed to observational economic data.

Contributors also have been citing some pretty...

The Pittsburgh Penguins are in the midst of another Stanley Cup playoff run. With a 3-1 lead over the Ottawa Senators, they are a mere 1 game away from their 3rd Eastern Conference Final in 6 years. But it looks like they will do so without starting goalie Marc-Andre Fleury.

After a string of disappointing playoff games, Fleury has been benched and netminder Tomas Vokoun has been guarding the goal. And Vokoun is playing so well that it doesn’t look like Fleury will see the ice anytime soon.

So what does this have to do with statistics? Well, Fleury’s statistics tell the story of why he is on...

I spend a majority of my time entrenched in statistics. Using statistics. Studying statistics. Developing and testing statistical software. Statistics guide many of my decisions at work and in life. That’s the world of an engineer.

For this reason, you can imagine my surprise when my husband called me at work on a bright, sunny June day in 2009 to tell me that our 4-year-old daughter had been diagnosed with Lyme disease. That, to me, seemed completely improbable. We live in a development in suburbia.  Our children don’t play deep in the woods. We don’t hike in the woods. In accordance with the...

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 different situations in which the Weibull distribution can help us make good decisions. The main reason Weibull is so useful is that it's very flexible in fitting different types of data, because it...

Have you ever seen those commercials where people are walking at a slant because they haven't had their V8? 

I was reminded of these ads recently when I had the opportunity to visit one of our Minitab customers in Tampa, Fl.  During the visit, I presented a seminar on some Advanced Minitab Tips and Tricks* using the same content we have presented in some of our free webinars. 

One of the very first scenarios in the presentation walks through data cleanup in your Minitab worksheet. As I started, I literally had to stop the class to address the commotion this topic kicked up on one side of the...