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

After my husband’s most recent visit to the dentist, he returned
home cavity-free...and with a $150 electric toothbrush in
hand.
I wanted details.
It began innocently. His dreaded trip to the dentist ended in
high praise for no cavities and only a warning to floss more. That
prompted my programming-and-automation-obsessed husband, still in
the chair, to exclaim, "I wish there was a way to automate... Continue Reading

The easiest way to determine the probability of being born on a
certain day is to assume that every day of the year has an equal
probability of being a birthday. But academic scholarship tends to
point to seasonal variation in births. If you average statistics
from the United Nations, the seasonality in the United States
of America from 1969 to 2013, excluding 1976 and 1977, looks like
this:
Seeing... Continue Reading

You have a column of categorical data. Maybe it’s a column of
reasons for production downtime, or customer survey responses, or
all of the reasons airlines give for those riling flight delays.
Whatever type of qualitative data you may have, suppose you want to
find the most common categories. Here are three different ways to
do that:
1. Pareto Charts
Pareto Charts easily help you separate the vital... Continue Reading

I’ve written about R-squared before and I’ve concluded that it’s
not as intuitive as it seems at first glance. It can be a
misleading statistic because a high R-squared is not always good and a low
R-squared is not always bad. I’ve even said that R-squared is overrated and that the standard error of the estimate (S) can be
more useful.
Even though I haven’t always been enthusiastic about... Continue Reading

Mind
the gap. It's is an important concept to bear in mind whilst
traveling on the Tube in London, the T in Boston, the Metro in
Washington, D.C., etc. But how many of us remember to mind the gap
when we create an interval plot in Minitab Statistical Software?
Not too many of us, I'd wager. And it's a shame, too.
When you travel on the subway, minding the gap means giving
thoughtful consideration... Continue Reading

When running a binary logistic regression and many other
analyses in Minitab, we estimate parameters for a specified model
based on the sample data that has been collected. Most of the time,
we use what is called Maximum Likelihood Estimation. However, based
on specifics within your data, sometimes these estimation methods
fail. What happens then?
Specifically, during binary logistic regression, an... Continue Reading

What is an interaction? It’s when the effect of one factor
depends on the level of another factor. Interactions are important
when you’re performing ANOVA, DOE, or a regression analysis.
Without them, your model may be missing an important term that
helps explain variability in the response!
For example, let’s consider 3-point shooting in the NBA. We
previously saw that the number of 3-point... Continue Reading

In my last post, I looked at
viewership data for the five seasons of HBO’s hit series Game of
Thrones. I
created a time series plot in Minitab that showed how
viewership rose season by season, and how it varied episode by
episode within each season.
My next step is to fit a statistical model to the data, which
I hope will allow me to predict the viewing numbers for future
episodes.
I am going to... Continue Reading

If you’ve not heard of the TV
series Game of
Thrones, you must have
been living on Mars for the past few years! An adaptation of the
fantasy series A Song of Ice
and Fire by George R. R.
Martin, the show is an epic tale of the political conflicts and
wars between noble houses in the fictional continents of Westeros
and Essos over who sits in the Iron Throne, and thus rules the
whole realm. (It was... Continue Reading

For the majority of my career with
Minitab, I've had the opportunity to speak at conferences and other
events somewhat regularly. I thought some of my talks were pretty
good, and some were not so good (based on ratings, my audiences
didn't always agree with either—but that's a topic for another
post). But I would guess that well over 90% of the time, my
proposals were accepted to be presented at... Continue Reading

While
the roots of Lean Six Sigma and other quality improvement
methodologies are in manufacturing, it’s interesting to see how
other organizational functions and industries apply LSS tools
successfully. Quality improvement certainly has moved far beyond
the walls of manufacturing plants!
For example, I recently had the opportunity to talk to Drew
Mohler, a Lean Six Sigma black belt and senior... Continue Reading

There's nothing like a boxplot, aka box-and-whisker diagram, to
get a quick snapshot of the distribution of your data. With a
single glance, you can readily intuit its general shape, central
tendency, and variability.
To
easily compare the distribution of data between groups, display
boxplots for the groups side by side. Visually compare the central
value and spread of the distribution for each... Continue Reading

In statistics, there are things you need to do so you can trust
your results. For example, you should check the sample size, the
assumptions of the analysis, and so on. In regression analysis, I
always urge people to check their residual plots.
In this blog post, I present one more thing you should do so you
can trust your regression results in certain
circumstances—standardize the continuous... Continue Reading

If you want to convince someone that at least a basic
understanding of statistics is an essential life skill, bring up
the case of Lucia de Berk. Hers is a story that's too awful to be
true—except that it is completely true.
A
flawed analysis irrevocably altered de Berk's life and kept her
behind bars for five years, and the fact that this analysis
targeted and harmed just one person makes it more... Continue Reading

When I wrote
How to Calculate B10 Life with Statistical
Software, I promised a
follow-up blog post that would describe how to compute any “BX”
lifetime. In this post I’ll follow through on that promise, and in
a third blog post in this series, I will explain why BX life is one
of the best measures you can use in your reliability
analysis.
As a refresher, B10 life refers to the time at which 10% of... Continue Reading

In this post, I’ll address some common questions we’ve received
in technical support about
the difference between fitted and data means, where to find each
option within Minitab, and how Minitab calculates each.
First,
let’s look at some definitions. It’s useful to have an example, so
I’ll be using the Light Output data set from Minitab’s Data Set
Library, which includes a description of the sample... Continue Reading

If
you follow the news in the United States then you’ve heard that
there’s a water crisis in Flint, Michigan. Although there’s going
to continue to be debate about how much ethics played a role in the
data collection practices, it’s worthwhile to at least be ready to
perform the correct analysis on the data when you have it. Here’s
how you can use Minitab to be like a citizen data scientist... Continue Reading

If you need to assess process
performance relative to some specification limit(s),
then process
capability is the tool to use. You collect some accurate
data from a stable process, enter those measurements in Minitab,
and then choose Stat > Quality Tools >
Capability Analysis/Sixpack or Assistant
> Capability Analysis.
Now, what about sorting the data?
I’ve been asked “why does Cpk change when I... Continue Reading

In the world of linear models, a hierarchical model contains all
lower-order terms that comprise the higher-order terms that also
appear in the model. For example, a model that includes the
interaction term A*B*C is hierarchical if it includes these terms:
A, B, C, A*B, A*C, and B*C.
Fitting the correct regression model can be as
much of an art as it is a science. Consequently, there's not always
a... Continue Reading

In my time at Minitab, I’ve gotten a good understanding of what
types of graphs users create. Everyone knows about histograms, bar
charts, and time series plots. Even relatively less familiar plots
like the interval plot and
individual value plot are still used quite often.
However, one of the most underutilized graphs we have available is
the area graph. If you’re not familiar with an Area... Continue Reading