Blog posts and articles about statistical principles in quality improvement methods like Lean and Six Sigma.

By Matthew Barsalou, guest
blogger.
Many statistical tests assume the data being tested came from a
normal distribution. Violating the assumption of normality can
result in incorrect conclusions. For example, a Z test may indicate
a new process is more efficient than an older process when this is
not true. This could result in a capital investment for equipment
that actually results in higher... Continue Reading

Design of Experiments is an extremely
powerful statistical method, we added a DOE tool to the Assistant
in Minitab 17 to make it more accessible to more
people.
Since it's summer here, I'm applying the
Assistant's DOE tool to outdoor cooking. Earlier, I showed
you how
to set up a designed experiment that will let you optimize how
you grill steaks.
If you're not already using it and you want to... Continue Reading

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Design of Experiments (DOE) has a reputation for difficulty, and
to an extent, this statistical method deserves that
reputation. While it's easy to grasp the basic idea—acquire the
maximum amount of information from the fewest number of
experimental runs—practical application of this tool can
quickly become very confusing.
Even
if you're a long-time user of designed experiments, it's still easy
to... Continue Reading

Last month the ESPN series Outside the Lines reported
on major league pitchers suffering serious injuries from being
struck in the head by line drives, and efforts MLB is making
towards having protective gear developed for pitchers. You can view
the report here if you'd like:
A couple of things jump out at me from the clip:
The overwhelming majority of pitchers are not interested in
wearing... Continue Reading

When data are collected in subgroups, it’s easy to understand
how the variation can be calculated within each of the subgroups
based the subgroup range or the subgroup standard deviation.
When data is not collected in subgroups (so the subgroup size is
1), it may be a little less intuitive to understand how
within-subgroup standard deviation is calculated. How does
Minitab Statistical Softwarecalcu... Continue Reading

Previously, I’ve written about
how to interpret regression coefficients and their individual P
values.
I’ve also written about
how to interpret R-squared to assess the strength of the
relationship between your model and the response variable.
Recently I've been asked, how does the F-test of the overall
significance and its P value fit in with these other statistics?
That’s the topic of this post!
In... Continue Reading

When someone gives you data to analyze, you can gauge how your
life is going by what you've received. Get a Minitab file, or even
comma-separated values, and everything feels fine. Get a PDF file,
and you start to think maybe you’re cursed because of your
no-good-dirty-rotten-pig-stealing-great-great-grandfather and wish
that you were someone else. For those of you who might be in such
dire... Continue Reading

I recently fielded an interesting question about the probability
and survival plots in Minitab Statistical
Software's Reliability/Survival menus:
Is there a one-to-one match
between the confidence interval points on a probability plot and
the confidence interval points on survival plot at a specific
percentile?
Now, this may seem like an easy question, given that the
probabilities on a survival plot... Continue Reading

The line plot is an incredibly
agile but frequently overlooked tool in the quest to better
understand your processes.
In any process, whether it's baking a cake or processing loan
forms, many factors have the potential to affect the outcome.
Changing the source of raw
materials could affect the strength of plywood a factory produces.
Similarly, one method of gluing this plywood might be better... Continue Reading

By Matthew Barsalou, guest
blogger.
Minitab Statistical Software
can assist us in our analysis of data, but we must make judgments
when selecting the data for an analysis. A good operational
definition can be invaluable for ensuring the data we collect can
be effectively analyzed using software.
Dr. W. Edwards Deming explains in Out of the Crisis
(1989), “An operational definition of safe,
round,... Continue Reading

Scientists who use the Hubble Space Telescope to explore the
galaxy receive a stream of digitized images in the form binary
code. In this state, the information is essentially worthless-
these 1s and 0s must first be converted into pictures before the
scientists can learn anything from them.
The same is true of statistical distributions and parameters that are used to describe sample data. They... Continue Reading

In Minitab Statistical Software,
putting a regression line on a scatterplot is as easy as choosing a
picture with a regression line on a scatterplot:
A neat trick is that you can also add calculated lines onto a
scatterplot for comparison or other communication purposes. Here’s
a demonstration.
United States Sentencing Guidelines
The
United States Sentencing Guidelines say how people who... Continue Reading

I've never understood the fascination with selfies.
Maybe it's because I'm over 50. After surviving the slings and
arrows of a half a century on Earth, the minute or two I spend in
front of the bathroom mirror each morning is more than
enough selfie time for me.
Still, when I heard that Microsoft had an online app that estimates
the age of any face on a photo, I was intrigued.
How would the app... Continue Reading

The NFL recently announced that after scoring a touchdown, teams
will be required to kick the extra point from the 15 yard line as
opposed to the 2 yard line. This is a pretty big change. And
whether you’re trying to improve the quality of your process, or
simply trying to make a sporting event more exciting, it’s always
good to know what kind of effects your change will have. So I’m
going to use... Continue Reading

In my previous post, I showed
you that the
coefficients are different when choosing (-1,0,1) vs (1,0) coding
schemes for General Linear Model (or
Regression).
We used the two different
equations to calculate the same fitted values. Here I will focus on
showing what the different coefficients represent.
Let's use the data and models from the last blog post:
We can display the means for
each level... Continue Reading

Since Minitab 17 Statistical
Software launched in February 2014, we've gotten
great feedback from many people have been using the General Linear
Model and Regression tools.
But in speaking with people as part of Minitab's Technical
Support team, I've found many are noticing that there are two
coding schemes available with each. We frequently get calls from
people asking how the coding scheme you... Continue Reading

Earlier, I wrote about the
different types of data statisticians typically encounter. In
this post, we're going to look at why, when given a choice in the
matter, we prefer to analyze continuous data rather than
categorical/attribute or discrete data.
As a reminder, when we assign something to a group or give it a
name, we have created attribute or
categorical data. If we count something,
like... Continue Reading

Over the past few years, the average length of an MLB game has
been steadily increasing. We can create a quick time series plot in
Minitab Statistical Software
to display this:
As games have been lasting
longer, there's been a feeling shared by many that this was a
negative. Games seemed to drag on, with a lot of unnecessary
stoppages and breaks.
To
combat this trend, and to try to speed up games to... Continue Reading

In
my previous post, I wrote about the hypothesis testing ban in
the Journal of Basic and Applied Social Psychology. I
showed how P values and confidence intervals provide important
information that descriptive statistics alone don’t provide. In
this post, I'll cover the editors’ concerns about hypothesis
testing and how to avoid the problems they describe.
The editors describe hypothesis testing... Continue Reading

If
you’ve checked out What’s
New in Minitab 17, you’ve had the chance to see that
Conditional Formatting leads the list. If you’ve been reading the
Minitab blog, you’ve had the chance to see demonstrations with
Marvel’s Avengers and the
Human Development Index. But you might not have had a chance to
see that you can highlight large standardized residuals from a
regression model and that the... Continue Reading