Minitab

In my last post, I talked about the danger of excluding interactions between factors in ANOVA and DOE models. Let’s now look at what can happen if you exclude an important factor altogether.

Warning: misleading high p-value up ahead...

Minitab regularly hosts webinars on different statistical topics. Let’s suppose we want to evaluate if certain webinar topics are more popular than others, so we collect data on the number of people who register for various sessions, including t-tests, control charts, design of experiments and Weibull analysis. Here’s an example of what the data might look like:

To test if the average number of registrants for all 4 webinar topics is equal, we can use analysis of variance (ANOVA). Here are the results using...

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 it.

In Minitab, you’ll find two tools that you can use to potentially transform your non-normal data into data that is normally distributed. Having...

This past week, the History Channel premiered a new show called the "United Stats of America." No, that's not a typo. It's a show hosted by twin brothers who are both standup comedians and obsessed with statistics. Since I'm also obsessed with statistics (I'm still working on the standup comedy part), I thought I'd check it out to see if I could relate any of their stats to common applications of Minitab Statistical Software.

The show attempts to reveal some of the most interesting and surprising statistics in America. For example, only 8% of teenage boys use soap when they wash their hands. And once a year a meteor the size of a boulder hits the Earth with the descructive force of an atomic bomb (don't worry, 70% of the Earth is covered in...

I got the chance recently to learn about how the United States Army used Minitab Statistical Software to improve a crucial internal process for deciding a soldier’s job status following a medical concern.

This decision is made through the MOS/Medical Retention Board Process (MMRB) and affects nearly 8,000 soldiers and their families per year, as well as numerous military commanders in charge of staffing.

The Army was taking an average of 61 days to reach decisions, and some outlier cases took as long as 400 days. The long lead time for this assessment kept soldiers’ careers in limbo, because they cannot deploy, make a permanent change of station, or go to school until a determination is made.

An Army Lean Six Sigma team set out to reduce the...

I remember a time in my career when I mistakenly thought I knew statistics—really knew statistics. It was before I met Yanling Zuo, Michelle Paret, Eduardo Santiago and a whole host of other Minitab statistical experts. I was a Quality Engineer and I’d been applying statistics for years. I assumed that the ability to design and run an experiment meant that I understood DOE. I assumed that years of process control meant that I understood control charting. I assumed that I’d use this knowledge to jump on the “fast track” to technical stardom.

It does not, and I did not.

I, in fact, knew a lot about the application of statistics and whole lot about quality engineering and testing. I knew those things well and I brought that knowledge with me...

The demands of modern life can make us very distracted.  

We should all do our best to slow down and not make sally mistakes. But it can be tough.  

With information coming at us from all directions, it's easy to get side-tracked and lose your …um, whatever.

But it's critical to prevent careless erors from creeping into your data. Because if you're not careful, a lot of innocent men may wind up getting pregnant by accident.

At least that's what happened to thousands of British men, who supposedly received gyneocological, obstetric, and other prenatal services over a two-year period, according to a recent letter in the British Medical Journal . 

But those men can relax...without Lamaze. Many were experiencing false pregnancies caused by...

Cirque du Soleil, the French circus known for its acrobatics, is currently on the road with its "Michael Jackson The Immortal World Tour" and made a stop just a few miles from the Minitab World Headquarters. 

My wife and I decided to go to the 8:00 show, but little did I know the performance would be preceded by a lesson in takt time...

Here is a timeline of events:

7:20 - A friend arrives to find long lines at each of the four arena entrances and doors closed.

7:30 - Doors are opened to allow ticket holders to enter after a weapons search (I still have not figured out why the potential assassination of a French acrobat felt like such a concern) and ticket scanning.

7:40 - My wife and arrive to find really long lines (it's 40 degrees F, windy,...

Ever make a task harder than it needs to be? Last night my son wanted to get a toy from a shelf in the closet that was a little beyond his reach. I watched as he tried to jump up and grab it.  Next, he started climbing the shelves (a quick word from me stopped that approach). Then he tried jumping several more times. Finally he said "I give up."

That's when I suggested he use the stepladder, which had been just inside the closet the whole time. 

Statistics can be like that. We can focus on the complexities of an analysis, but lose sight of the practical question we're trying to answer. If we step back and look at all of the available tools, sometimes there's a simpler way to get the information we need. 

When seeking to improve quality, you...

Clint Eastwood, playing Dirty Harry, asked this famous question while confronting a bad guy who was about to reach for his rifle. I’m quite sure that the bad guy carefully pondered the nature of luck, probabilities, and expected outcomes before deciding not to grab his rifle!

A month ago, I did something shocking . . . something that I hadn’t done for several decades. Just like the bad guy in the Dirty Harry movie, I started thinking about luck. Yes, you guessed it:  I bought a lottery ticket for the record-breaking Mega Millions Jackpot. This purchase is shocking for someone like me who knows statistics and is fully aware of how unlikely it is to win. Did I feel lucky? Or was I just a punk?

What Is Luck?

Luck involves probabilities and...

In the last post, we discussed how general full factorial designs let you study factors at more than two levels. The remaining 4 options that Minitab offers for factorial design of experiments are all 2-level designs, including the Plackett-Burman design.

Because there are 4 different kinds of 2-level designs, one of which is selected by default, you can probably guess that 2-level designs are quite popular. So what’s special about a 2-level design, and why would we use one?

One of the benefits of using design of experiments to plan data collection is to learn as much as possible from the smallest amount of data. One important method to achieve this benefit is sequential experimentation: we collect some data to find out if we have to collect...

I think it’s neat to find examples of Lean Six Sigma techniques in restaurants and stores when I’m out to eat or shopping. What started as a philosophy in the manufacturing world seems to be transcending into our everyday shopping experiences, and even into the products we choose to add to our carts.

Here’s a recap from my latest “Lean” shopping escapade:

I was recently in a grocery store snack aisle when I came across a bag of dark potato chips.

I thought this was a great use of a snack manufacturer taking what is usually considered a defect and turning it into a source of revenue. Of course some market research needs to happen to make sure people actually want to buy the overcooked chips, but what a brilliant way to turn waste into a...

Last time, I shared some useful tools for handling date and time data. But Minitab has many other useful tools for manipulating date/time data that you might not be aware of. Let’s take a look at a few more helpful tips and tricks.

Extracting Information from a Date/Time Column

If you look under the Data menu, you’ll notice Extract from Date/Time > To Numeric or To Text. This function allows you to take one or multiple components that make up your date/time values and transform it into a new data format.

The table below illustrates the conversion that takes place when you select Quarter and Year using both extraction methods, To Numeric and To Text:

After extracting to a text column, you...

In my last blog post, I used Minitab Statistical Software to try to determine whether Mel Kiper or Todd McShay is better at predicting the 1st round of the NFL draft. Just like you might need to decide between suppliers in a quailty improvement situation, I needed to decide who to go with when I filled out my 2012 NFL Mock Draft Office Pool. Well, as it turns out there wasn't any statistical difference between the two, and the cost was exactly the same. So I just flipped a coin to decide who to go with, and it came up Kiper!

Now that the first round of this year's draft is complete, I can do some data analysis on his picks and see how accurate they were. Then I'll do the same with McShay and see if the coin made the right decision.

My son goes to the same high school as infamous Aussie rocker Angus Young, from AC/DC. If the school provided any of the inspiration for songs like “Highway to Hell” and “Dirty Deeds Done at a Discount”, I think my son will learn a lot there. In fact, he might even learn that gambling doesn’t pay.

On weekday mornings, I often walk my son to school and then hop a train into the city. As we’re approaching the school, we pass a club where they feature gambling. When we pass the club, I often say, “Hey, son. Wait here for a minute and I’ll go double your lunch money.” That always gets a big laugh. And when I’m done laughing, I get to enjoy my son’s disgusted expression as he explains, again, that the joke is not funny and has never been funny.

But...

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, analyzing data from medical studies around the globe.

Here are a few studies that caught my eye...
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If a baby is born...

In my last post I talked about why you need to check your regression analysis residuals. In a nutshell, your predictors should be so good at explaining (or predicting) the response that only the inherent randomness of any real-world phenomenon remains leftover for the error portion. If you observe explanatory or predictive power in the error, you know that your predictors are missing some of the predictive information. In this post I'll cover a specific type of pattern that you can see in the residuals and show you how to fix the problem.

Regression residuals should have a constant spread across all fitted values. If your plot looks like the one below, you've got a problem known as heteroscedasticity or non-constant variance. You can see...

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 examples from manufacturing companies. For many process improvement professionals, SPC techniques for controlling process variation and avoiding product...

In honor of the 100^th anniversary of the sinking of the Titanic, we recently posted a dataset on the passengers aboard the ship that included Class (coach or first), Gender (female or male), Age, and Status (survived or died).  From Age an additional column was created indicating Child (17 years or younger) or Adult (18 years or older).

In an earlier post, we showed how survival rates could be compared between levels of one variable—for example, females versus males—using Stat > Tables > Cross Tabulation and Chi Square.  But what if we wanted to take all factors into consideration to paint a complete picture of survival rates?

Applying Binary Logistic Regression

In Minitab Statistical Software, Stat > Regression > Binary Logistic Regression a...

Whether you're a Lean Six Sigma black belt, a researcher, or a statistics student, at some point you will need to work with data that involve either dates, times, or both. Do you know where all of your date/time tools are? Let’s take a quick trip through Minitab Statistical Software and see what it has to offer for date/time data:

Column Indicators of Date and Time Data

You will know when Minitab recognizes a column as a date/time format if it has a “-D” to the right of the number, as in “C1-D”.  If Minitab recognizes the column as text data, you’ll see a “C1-T.” If it’s numeric data, nothing will appear to the right of C1.

Changing a Column into Date/Time Format

Minitab tries to determine column formats when you paste data into a worksheet,...

It’s a common occurrence in any quality improvement situation: You have 2 (or more) suppliers that offer you the same product. How do you decide which one to choose? You could just flip a coin. But that wouldn’t be very sensible, would it? No, instead it’s probably best to do some data analysis to help you make your decision.

So what does this have to do with the NFL draft? Well, everybody and their brother are drawing up mock drafts right now. There are different suppliers offering me the same product! How do I know which one to use when I fill out my NFL Mock Draft Office Pool (that’s a thing, right)? Well, that’s where Minitab comes in. I’m going to look back at some mock drafts from previous years and see just how accurate they were.

For...