Businesses are getting more and more data from existing and
potential customers: whenever we click on a web site, for example,
it can be recorded in the vendor's database. And whenever we use
electronic ID cards to access public transportation or other
services, our movements across the city may be analyzed.
In the very near future, connected objects such as cars and
electrical appliances will... Continue Reading
last thing you want to do when you purchase a new piece of software
is spend an excessive amount of time getting up and running. You’ve
probably been ready to the use the software since, well,
yesterday. Minitab has always focused on making our
software easy to use, but many professional software packages do
have a steep learning curve.
Whatever package you’re using, here are three things you... Continue Reading
Suppose you’ve collected data on cycle time, revenue, the
dimension of a manufactured part, or some other metric that’s
important to you, and you want to see what other variables may be
related to it. Now what?
When I graduated from college with my first statistics degree,
my diploma was bona fide proof that I'd endured hours and hours of
classroom lectures on various statistical topics, including
Do you recall my “putting the cart before the horse” analogy in
part 1 of this blog series? The comparison is simple.
We all, at times, put the cart before the horse in relatively
innocuous ways, such as eating your dessert before you’ve eaten
your dinner, or deciding what to wear before you’ve been invited to
the party. But performing some tasks in the wrong order, such as
running a statistical... Continue Reading
Analysis of variance (ANOVA) can determine whether the means of
three or more groups are different. ANOVA uses F-tests to
statistically test the equality of means. In this post, I’ll show
you how ANOVA and F-tests work using a one-way ANOVA example.
But wait a minute...have you ever stopped to wonder why you’d
use an analysis of variance to determine whether
means are different? I'll also show how... Continue Reading
In statistics, t-tests are a type of hypothesis test that allows
you to compare means. They are called t-tests because each t-test
boils your sample data down to one number, the t-value. If you
understand how t-tests calculate t-values, you’re well on your way
to understanding how these tests work.
In this series of posts, I'm focusing on concepts rather than
equations to show how t-tests work.... Continue Reading
T-tests are handy hypothesis tests in statistics when you want to
compare means. You can compare a sample mean to a hypothesized or
target value using a one-sample t-test. You can compare the means
of two groups with a two-sample t-test. If you have two groups with
paired observations (e.g., before and after measurements), use the
How do t-tests work? How do t-values fit in? In this... Continue Reading
Likert scales are commonly associated with surveys and are used in
a wide variety of settings. You’ve run into the Likert scale if
you’ve ever been asked whether you strongly agree, agree, neither
agree or disagree, disagree, or strongly disagree about something.
The worksheet to the right shows what five-point Likert data look
like when you have two groups.
Because Likert item data are... 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
1. Pareto Charts
Pareto Charts easily help you separate the vital...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 need to assess process
performance relative to some specification limit(s),
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
If you perform linear regression analysis, you might need to
compare different regression lines to see if their constants and
slope coefficients are different. Imagine there is an established
relationship between X and Y. Now, suppose you want to determine
whether that relationship has changed. Perhaps there is a new
context, process, or some other qualitative change, and you want to
determine... Continue Reading
When you work in data analysis, you quickly discover an
irrefutable fact: a lot of people just can't stand
statistics. Some people fear the math, some fear what the data
might reveal, some people find it deadly dull, and others think
it's bunk. Many don't even really know why they hate
statistics—they just do. Always have, probably always
Problem is, that means we who analyze data need to
com... Continue Reading
Back when I was an undergrad in
statistics, I unfortunately spent an entire semester of my life
taking a class, diligently crunching numbers with my TI-82, before
realizing 1) that I was actually in an Analysis of Variance (ANOVA)
class, 2) why I would want to use such a tool in the first place,
and 3) that ANOVA doesn’t necessarily tell you a thing about
Fortunately, I've had a lot more... Continue Reading
Control charts are a fantastic tool. These charts plot your
process data to identify common cause and special cause variation.
By identifying the different causes of variation, you can take
action on your process without over-controlling it.
Assessing the stability of a process can help you determine
whether there is a problem and identify the source of the problem.
Is the mean too high, too low,... Continue Reading
Easy access to the right tools makes any task easier. That
simple idea has made the Swiss Army knife essential for
adventurers: just one item in your pocket gives you instant access
to dozens of tools when you need them.
If your current adventures include analyzing data, the Editor
menu in Minitab
Statistical Software is just as essential.
Minitab’s Dynamic Editor Menu
Any job goes more smoothly... Continue Reading
approaches, you are probably taking the necessary steps to protect
yourself from the various ghosts, goblins, and witches that are prowling
around. Monsters of all sorts are out to get you, unless they’re
sufficiently bribed with candy offerings!
I’m here to warn you about a ghoul that all statisticians and
data scientists need to be aware of: phantom degrees of freedom.
These phantoms... Continue Reading
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