I love the field of statistics. It gives us the ability to remove human bias and opinion to discern between what is truly important - and significant - from those things that are not.

For instance, have you ever been at a meeting where a time series plot is displayed up on the screen and someone declares there is a spike in the data? Well, according to what? Let's use the power of statistics and control charts to put some limits on that puppy so we can be sure!

I love statistics so much that I earned both my undergrad and graduate degrees on the subject. (I'm an outlier, I know.) Although my...

Measurement systems analysis (MSA) is essential to the success of any data analysis. If you cannot rely on the tool you’re using to take measurements, then why bother collecting data to begin with? It would be like trying to lose weight while relying on a scale that doesn’t work. What’s the point in weighing yourself?

Minitab Statistical Software offers many types of tools that you can use to assess your measurement system, including:

• Gage R&R Study (Crossed)
• Gage R&R Study (Nested)
• Attribute Agreement Analysis

Destructive Testing Defined

In MSA studies for continuous measurements (e.g. weight,...

In my last post, I used U.S. Census Bureau data and correlation to reveal that people living in colder, more crowded states typically make more money. I’m sure there is some rationale to support this conclusion, but I’ll leave that explanation up to the economists. Meanwhile, let's you and me move on to more statistics…

Once I discovered there was correlation between income and other census data, I decided to use Minitab Statistical Software to find a regression model and further examine the relationship. Easy, right?

That’s what I thought, too.

In fact, I wasn't even planning on writing about...

I recently read an article about how the United States median household income has declined the last two years in a row. While that should make most of us as joyful as a vegetarian who just won a lifetime supply of beef jerky, there are some states that have median household incomes well above the norm.

So, any guesses as to which state is the best at over $70K, and which is the worst at nearly half that amount? Here's a hint: both states start with the letter M.

If you guessed Maryland and Mississippi, respectively, you’d be right.

The article then went on to list the top 5 states at both...

Trying to remember what the alpha-level, p-value, and confidence interval all mean for a hypothesis test—and how they relate to one another—can seem about as daunting as Dorothy’s trek down the yellow brick road.

Rather than sitting through a semester of Intro Stats, let's get right to the point and explain in clear language what all these statistical terms mean and how they relate to one another.

What Does Alpha Mean in a Hypothesis Test?

Before you run any statistical test, you must first determine your alpha level, which is also called the “significance level.” By definition, the alpha level...

A statistician walks into a party. The host looks up and says “Welcome! Let me introduce you to everyone. This is John, Jeff, Jill, another Jeff, Petra, Porter, Paxtyn and Chris.” The statistician declares, “I love parties that exhibit properties of the Pareto principle!”

The host—not a statistician—slowly turns and walks away, befuddled and bewildered.

True story? Almost, except I kept inner monologue about the Pareto principle to myself!

A Little Pareto Chart History

Back in the early 1900s, engineer, economist and sociologist, Vilfredo Pareto made a similar observation. However, it wasn’t about...

If you're one of the gazillion people who have read The Hunger Games, then you’re quite familiar with “Real or Not Real?” And if you haven't read it, I'm guessing you've at least heard about this best-selling trilogy.

The Hunger Games movie, like the book, has been a huge success, grossing over $400 million domestically. I recently saw an ad for the DVD to be released on August 18 and it got me thinking. Could I use statistics to predict DVD sales? If my model below is as good as it looks, then the answer is "yes."

Or should I say, “real”?

Creating a Statistical Model: Where to Begin?

I rarely...

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...

I couldn’t wait to get to the Guinness brewery after landing in Dublin. Yes, I was eager to taste a pint nearly fresh off the line, but I was also curious to see if there would be any indication that the brewery was home to arguably one of THE most important developments in the field of statistics. I was not disappointed.

There on the wall in the old Guinness Storehouse was a lone plaque paying homage to William Sealy Gosset. Unfortunately, none of the other tourists had a clue why my husband and I hurried towards it to snap some photos. But I digress...

More than a century ago, and well before...

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...

Do you prefer ketchup or soy sauce?

If someone asked you this question, your answer would likely depend upon what you were eating. You probably wouldn't dunk your spicy tuna roll in ketchup. And most people (pregnant moms-to-be excluded) don't seem to fancy eating soy sauce with hot French fries.

A Common Error When Using ANOVA or DOE to Assess Factors

Modeling techniques such as ANOVA or Design of Experiments (DOE) can determine if factors of interest impact a process. For example, you may want to evaluate how various time and temperature settings affect product quality. Or you may want to...

We always hear about the "average" of this and the "average" of that…the average temperature, the average price of gasoline, the average number of children per household, etc.  In fact, I just saw an article on average student math scores by country.

If you're a college grad, take a minute to recall when you were choosing your major. For those of us with aspirations of making big bucks, studying to become a doctor, lawyer, or CEO are some of the more lucrative career paths that may have come to mind.

Well, what if I told you that back in the mid-1980's at the University of North Carolina, the...

Variation is everywhere. It’s in your daily commute to work, it’s in the amount of caffeine you drink every day, in the number of e-mails that arrive in your inbox, etc. Whether you’re monitoring something as ordinary as caffeine consumption or something more important like a multi-million dollar manufacturing process, you can use one simple tool to monitor variation and determine whether the variation you’re seeing is due to natural random fluctuation or if your process is out of control due to some special cause.

The tool I’m referring to is the all-powerful control chart.

Now here's where it...

Happy Groundhog Day!

For those of you who are not familiar with this crazy American holiday (or have yet to see the Bill Murray movie by the same name), every year on February 2nd thousands of excited onlookers gather in a small Pennsylvania town named Punxsutawney to find out if spring will come early or if we’ll have to wait another dreaded 6 weeks for winter to end.

And how do we learn what the prognostication will be? From Punxsutawney Phil, of course, the beloved groundhog.

If Punxsy Phil sees his shadow and retreats back into his comfy burrow, another six weeks of winter there will be....