Blog posts and articles with tips for using statistical software to analyze data for quality improvement.

In regression
analysis, overfitting a model is a real problem. An overfit model
can cause the regression coefficients, p-values, and R-squared to be misleading. In this post,
I explain what an overfit model is and how to detect and avoid this
problem.
An overfit model is one that is too complicated for your data
set. When this happens, the regression model becomes tailored to
fit the quirks and... Continue Reading

To make objective
decisions about the processes that are critical to your
organization, you often need to examine categorical data. You may
know how to use a t-test or ANOVA when you’re comparing measurement
data (like weight, length, revenue, and so on), but do you know how to compare
attribute or counts data? It easy to do with statistical software
like Minitab.
One person may look at
this bar... Continue Reading

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When we take pictures with a
digital camera or smartphone, what the device really does
is capture information in the form of binary code. At the most
basic level, our precious photos are really just a bunch of 1s and
0s, but if we were to look at them that way, they'd be pretty
unexciting.
In its raw state, all that
information the camera records is worthless. The 1s and 0s need to be converted... Continue Reading

If
you want to use data to predict the impact of different variables,
whether it's for business or some personal interest, you need to
create a model based on the best information you have at your
disposal. In this post and subsequent posts throughout the football
season, I'm going to share how I've been developing and applying a
model for predicting the outcomes of 4th down decisions in Big... Continue Reading

by Colin Courchesne, guest blogger, representing his
Governor's School research team.
High-level research opportunities for high school students are
rare; however, that was just what the New Jersey Governor’s School
of Engineering and Technology provided.
Bringing together the best and brightest rising seniors from
across the state, the Governor’s School, or GSET for short, tasks
teams of... Continue Reading

Statisticians say the darndest things. At least, that's how it
can seem if you're not well-versed in statistics.
When I began studying statistics, I approached it as a language.
I quickly noticed that compared to other disciplines, statistics
has some unique problems with terminology, problems that don't
affect most scientific and academic specialties.
For
example, dairy science has a highly... Continue Reading

Last time, I told you how I had double-checked the analysis in
a post that involved running the Johnson transformation on a set of
data before doing normal capability analysis on it. A reader asked why the transformation didn't
work on the data when you applied it outside of the capability
analysis.
I hadn't tried transforming the data that way, but if the transformation worked when performed
as... Continue Reading

I don't like the taste
of crow. That's a shame, because I'm about to eat a huge helping of
it.
I'm going to tell you
how I messed up an analysis. But in the process, I learned some new
lessons and was reminded of some older ones I should remember to
apply more carefully.
This Failure Starts in
a Victory
My mistake originated in the
2015 Triple Crown victory of American Pharoah. I'm no... Continue Reading

Every now and then I’ll test my
Internet speed at home using such sites as http://speedtest.comcast.net or http://www.att.com/speedtest/. My need to perform these tests could
stem from the cool-looking interfaces they employ on their site, as
they display the results using analog speedometers and RPM meters.
They could also stem from the validation that I need in "getting
what I am paying for,"... Continue Reading

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

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

Before I joined Minitab, I worked for many years in Penn State's
College of Agricultural Sciences as a writer and editor. I
frequently wrote about food science and particularly food safety,
as I regularly needed to report on the research being conducted by
Penn State's food safety experts, and also edited course materials
and bulletins for professionals and consumers about ensuring they
had safe... 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

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

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

The first summer
blockbuster of 2015 was released two weeks ago—The Avengers:
Age of Ultron. The first Avengers film featured a pretty well
known cast of superheroes (if, of course, you’re a superhero fan).
However, in the 40-year run of the Avengers comic book, that team
has evolved to keep the material fresh and to allow some characters
to go their solo ways.
I
want to use Minitab's statistical... Continue Reading