3 Common (and Dangerous!) Statistical Misconceptions

Have you ever been a victim of a statistical misconception that’s affected how you’ve interpreted your analysis? Like any field of study, statistics has some common misconceptions that can trip up even experienced statisticians. Here are a few common misconceptions to watch out for as you complete your analyses and interpret the results.

Mistake #1: Misinterpreting Overlapping Confidence Intervals

When comparing multiple means, statistical practitioners are sometimes advised to compare the results from confidence intervals and determine whether the intervals overlap. When 95%...

Starting Out with Capability Analysis

It's your first day at the Jedi Temple, working as a lightsaber manufacturer. Your first task on the job is to run a Capability Analysis on the length of lightsabers being produced. Your main concern is to see if the lightsabers fit within the requried length specifications set forth by the Jedi Council. You aren’t quite sure where to start. Thankfully, Minitab Statistical Software is there to help you—even in a galaxy far, far away.

Capability Analysis is used to assess the capability of an in-control process. A "capable" process is able to produce products or services that meet...

Beyond the "Regular Guy" Control Charts: An Ode to the EWMA Chart

It's no secret that in the world of control charts, I- and Xbar- are pretty much the popular kids in school.  But have you ever met their cousin EWMA? That's him in the middle of the class, wearing the clothes that look nice but aren't very flashy. You know, when Xbar- and I- were leading the championship football team last month, EWMA won the state tennis championship?  I didn't go either -- pretty much only the player's parents go to tennis matches -- but I heard that he won it.  Someone told me he even got a scholarship to an Ivy League school to play, not that he needed it with his grades...

A Story-based Approach to Learning Statistics (and Statistical Software)

Want to learn more about analyzing data? Try taking a page from Aesop's book. 

Well...really, I'm suggesting taking multiple pages from Minitab's book, but my suggestion stems from an idea that Aesop epitomizes.  

Aesop was no fool. When he wanted to convey even the heaviest of lessons, he didn't waste time detailing the intellectual and philosophical arguments behind them. He didn't argue, cajole, or berate. He didn't lecture or pontificate. 

He told a story. 

Minitab uses the same approach in Meet Minitab, the introductory guide to data analysis and quality statistics using our statistical...

My Work with Minitab

The Minitab Fan section of the Minitab blog is your chance to share with our readers! We always love to hear how you are using Minitab products for quality improvement projects, Lean Six Sigma initiatives, research and data analysis, and more. If our software has helped you, please share your Minitab story, too!

Throughout my 15 years as a Six Sigma Initiative Leader, Consultant, Trainer, Black Belt and master Black Belt I have been enthusiastic about Minitab Statistical Software, starting from release 11 to now.

Minitab's graphics are outstanding in their ability to present messages and...

Mayberry, Ppk: Making Intuitive Sense of Capability Output (Episode 2)


Sheriff Taylor: Remember the talk we had awhile back about Pp?

Barney: Keep talking like a potty mouth, Andy, and Aunt Bea’s going to wash your mouth out with soap!

Sherriff Taylor (sighs): So you remember that Pp is the ratio of the specification spread to—

Barney (interrupts): —the process spread! Yeah, yeah, I got all that. And the smaller your car (process spread), relative to its parking space (specification spread), the higher Pp will be—and the more capable your process. But it makes me wonder, Andy.

Sherriff Taylor: About what?

Barney: What’s the legal requirement for Pp? When should we...

Mayberry, Ppk: Making Intuitive Sense of Capability Output (Episode 1)

Sheriff Taylor: What’s wrong Barney?

Barney: Someone spilled alphabet soup all over my capability output! Wait till I catch the practical joker who did this!! They’ll be sorry!!

Sheriff Taylor: That’s not alphabet soup, Barney. Those are capability indices.

Barney: I don’t see any indecisives, Andy. I just see a big mess of letters: Cp, Pp, Cpk, Ppk, Cpm, PPM…LMAO!

Sheriff Taylor: LMAO is not part of capability output, Barney. At any rate, the indices help you evaluate whether your process is meeting your customer requirements.

Barney: Well, my customers don’t require random letters of the...

Design of Experiments for an Avid Gamer

The Minitab Fan section of the Minitab blog is your chance to share with our readers! We always love to hear how you are using Minitab products for quality improvement projects, Lean Six Sigma initiatives, research and data analysis, and more. Today we learn how an avid gamer used design of experiments to boost his performance in his favorite driving game.

If our software has helped you, please share your Minitab story, too!


I've used Minitab Statistical Softwarepretty much every work day since being a Black Belt, but I've also used it at home. Back before the needs of family life took over,...

PolyOne’s Lean Six Sigma Success

I recently had the chance to talk to Brett Warland, global director of process improvement at PolyOne Corporation. The word “global” is often present in the titles of many organization’s process improvement programs and employee job titles that deal with quality. This can convey not only an international emphasis on process improvement at worldwide branches of the company, but also that CI methods pervade each aspect of the business’s culture and day-to-day workings.

I definitely found this to be the case at PolyOne! Just a few minutes into our conversation, Brett mentioned that...

Managing Diabetes with Six Sigma and Statistics, Part II

In my last post, I discussed how quality professional Bill Howell chose to manage his diabetes diagnosis by treating it as a Six Sigma project. Since a key metric in controlling his disease was keeping his blood glucose levels below 125 mg/dL, he tested his blood using a meter three times per day and then charted his data to see how his levels changed over time. He ensured his measurement systems were producing reliable data, and assessed the potential causes for his increased blood glucose levels. He then chose to focus on the causes he could control and analyze himself.

Tracking Daily...

Process Capability Statistics: Cpk vs. Ppk

Back when I used to work in Minitab Tech Support, customers often asked me, “What’s the difference between Cpk and Ppk?” It’s a good question, especially since many practitioners default to using Cpk while overlooking Ppk altogether. It’s like the '80s pop duo Wham!, where Cpk is George Michael and Ppk is that other guy.

Poofy hairdos styled with mousse, shoulder pads, and leg warmers aside, let’s start by defining rational subgroups and then explore the difference between Cpk and Ppk.

Rational Subgroups

A rational subgroup is a group of measurements produced under the same set of conditions. Subg...

Regression Smackdown: Stepwise versus Best Subsets!

In my last post, I professed my fondness for regression analysis. This time, I’m going compare two automatic tools that will help you to create a good regression model.

Imagine a scenario where you have many predictor variables and a response variable. Because there are so many predictor variables, you’d like some help in creating a good regression model. You could try a lot of combinations on your own. But, you’re in luck! Minitab Statistical Software has not one, but two automatic tools that will help you pick a regression model.

These tools are Stepwise Regression and Best Subsets...

Transformers! Normal Data in Disguise?

Many statistical analyses require an assumption of normality. In cases when your data are not normal, sometimes you can apply a function to make your data approximately normal so that you can complete your analysis.

If you've seen any of the Transformers movies, you know that these extraordinary robots can, with some Hollywood magic, turn themselves into apparently normal items like cars and appliances.

You may not get quite the same special-effects thrill, but when you have an extraordinary (i.e., non-normal) data set, Minitab Statistical Software can pull a Transformers-like metamorphosis on...

A Minitab Trainer in Action!

Have you ever wondered what a day with a Minitab trainer might be like? Maybe you’ve thought about taking a Minitab public training course, but you weren’t sure how the class is structured or what kinds of examples are used during instruction. To give you a taste of training, check out this neat video of Minitab technical training specialist, Eduardo Santiago, in action!

In the full-hour of training documented in the video below, Eduardo covers topics related to Statistical Process Control (SPC) and illustrates statistical techniques used to monitor and control processes with real-world...

Why Minitab May Be Beneficial For Your Health

I don’t know about you, but I’m thankful we no longer live in a time when we feel compelled to swig swamp-root juice any time we want to feel better. The field of medicine couldn’t advance by relying solely on subjective anecdotes and testimonials, like those for Dr. Kilmer’s cure-all.

Using statistical analyses, we can now objectively evaluate various preventions and treatments in measurable, quantitative ways.

Curious to see what Minitab Statistical Software was up to in healthcare and medicine lately, I ran a Medline search. In the past year, the software has been busy making the rounds,...


When I first started learning about Lean Six Sigma and familiarizing myself with all the different terminology and methodologies, I was a little overwhelmed and confused by all the acronyms. FMEA, C&E Matrix, Gage R&R, SIPOC, DMAIC…the list goes on and on!

However, I really got tripped up by the similar-sounding acronyms of DMAIC, DMADV, and DFSS. These acronyms stand for the most common Lean Six Sigma project methodologies, which help quality improvement practitioners keep their projects focused with an established route to follow for completion. Each methodology is made up of five phases and...

Tip 3: Gain Confidence with Confidence Intervals

New to confidence intervals?  Here are some important things to keep in mind!

Confidence Intervals:

  • are used to estimate population parameters (commonly the process mean, standard deviation, % of defective units, or even capability indices). 
  • provide more meaningful information than any random sample statistic for characterizing the population.

See “Tip 1: Every sample statistic is a little bit wrong.”

When your 95% confidence interval for the mean is (μlow, μhigh), you can be 95% confident that the population (process) mean, μ, is between μlow and μhigh …and 5% confident that μ is not betwe...

Weibull Wobble? Process Capability Analysis with Nonnormal Data

Manufacturers need to make items that meet a customer’s standards, or they’ll soon be out of business. That’s why quality engineers devote a good deal of time to making sure that processes are able to meet those standards. 

The first step is to make sure your process is stable. After all, you can’t predict the performance of an unstable process. But you can predict and improve on a stable process. 

If we know our process is stable, we can use a statistical technique called process capability analysis to see if the process is capable of consistently producing products that meet...

Using Macros to Publish Statistical Reports

Macros are very useful for automating and processing sequences of repetitive tasks. For example, generating periodic reports (weekly, monthly or quarterly) often becomes a very tedious and time-consuming activity. The graphs and statistical analyses contained in these reports need to be updated regularly and are always the same (although the data change).

Fortunately, these repetitive tasks can easily be automated with the help of some very simple macros.

You do not need to become a macro expert to automate long sequences of tasks. I'm going to present an example of how graphs and statistical...

Questions about Capability Statistics - Part 2

Another thing you may notice when performing a Capability Analysis in Minitab is the option to change whether you want to see capability statistics (Cp, Pp…) or Z.Bench.  From Minitab Help:
“A disadvantage of the Cpk index is that it only represents one side of the process curve, and tells you nothing about the other extreme. For example, the two graphs below display processes with identical Cpk values. However, one violates both specification limits, and the other only violates the lower specification limit...”

The Z in Z.Bench refers to the standard normal distribution with mean 0...