True or false: When comparing a parameter for two sets of
measurements, you should always use a hypothesis test to determine
whether the difference is statistically significant.
The answer? (drumroll...) True!
...and False!
To understand this paradoxical answer, you need to keep in mind
the difference between samples, populations, and descriptive and
inferential statistics.
Descriptive Statistics and... Continue Reading

Today,
September 16, is World Ozone Day. You don't hear much about the
ozone layer any more.
In fact, if you’re under 30, you might think this is just
another trivial, obscure observance, along the lines of International Dot Day (yesterday) or National Apple Dumpling Day (tomorrow).
But there’s a good reason that, almost 30 years ago, the United
Nations designated today to as a day to raise... Continue Reading

Statistics is all about modelling. But that doesn’t mean strutting down the
catwalk with a pouty expression.
It means we’re often looking for a mathematical form that best
describes relationships between variables in a population, which we
can then use to estimate or predict data values, based on known
probability distributions.
To aid in the search and selection of a “top model,” we often
utilize... Continue Reading

It's
been called a "demographic watershed".
In the next 15 years alone, the worldwide population of
individuals aged 65 and older is projected to increase more
than 60%, from 617 million to about 1 billion.1
Increasingly, countries are asking themselves: How can we
ensure a high quality of care for our growing aging
population while keeping our healthcare costs under control?
The answer? More... Continue Reading

What does the eyesight of a homeless person have in common with
complications from dental anesthesia? Or with reducing
side-effects from cancer? Or monitoring artificial hip
implants?
These are all subjects of recently published studies that
use statistical
analyses in Minitab to improve healthcare
outcomes. And they're a good reminder that when we
improve the quality of healthcare for others, we... Continue Reading

The
Pareto chart is a graphic representation of the 80/20 rule, also
known as the Pareto principle. If you're a quality improvement
specialist, you know that the chart is named after the early 20th
century economist Vilfredo Pareto, who discovered that roughly 20%
of the population in Italy owned about 80% of the property at that
time.
You probably also know that the Pareto principle was... Continue Reading

About
a year ago, a reader asked if I could try to explain
degrees of freedom in statistics. Since then,
I’ve been circling around that request very cautiously, like it’s
some kind of wild beast that I’m not sure I can safely wrestle to
the ground.
Degrees of freedom aren’t easy to explain. They come up in many
different contexts in statistics—some advanced and complicated. In
mathematics, they're... Continue Reading

I
live with a German national, who often tells me that we Americans
spend way too much of our lives at work. He also
frequently comments that we work much less efficiently than Germans
do, during the increased time we’re at work.
Which reminds me—I need to pay my water bill online...
Okay, I’m back. Quick, wasn’t it? So convenient. Now, where was
I? Oh, work habits.
After checking the hourly weather... 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

How deeply has statistical content from Minitab blog posts (or
other sources) seeped into your brain tissue? Rather than submit a
biopsy specimen from your temporal lobe for analysis, take this
short quiz to find out. Each question may have more than one
correct answer. Good luck!
Which
of the following are famous figure skating pairs, and which are
methods for testing whether your data follow a... Continue Reading

Did
you ever wonder why statistical analyses and concepts often have
such weird, cryptic names?
One conspiracy theory points to the workings of a secret
committee called the ICSSNN. The International Committee for
Sadistic Statistical Nomenclature and Numerophobia was formed
solely to befuddle and subjugate the masses. Its mission: To select
the most awkward, obscure, and confusing name possible... Continue Reading

If
you use ordinary linear regression with a response of count data,
if may work out fine (Part
1), or you may run into some problems (Part
2).
Given that a count response could be problematic, why not use a
regression procedure developed to handle a response of counts?
A Poisson regression analysis is designed to analyze a
regression model with a count response.
First, let's try using Poisson... Continue Reading

My previous post showed an example of using
ordinary linear regression to model a count response. For that particular count data, shown by the blue
circles on the dot plot below, the model assumptions for linear
regression were adequately satisfied.
But frequently, count data may contain many values equal or
close to 0. Also, the distribution of the counts may be
right-skewed. In the quality field,... Continue Reading

Ever use dental floss to cut soft cheese? Or Alka Seltzer to
clean your toilet bowl? You can find a host of nonconventional uses for ordinary objects
online. Some are more peculiar than others.
Ever use ordinary linear regression to evaluate a response
(outcome) variable of counts?
Technically, ordinary linear regression was designed to evaluate
a a continuous response variable. A continuous... 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

It’s usually not a good idea to rely solely on a single
statistic to draw conclusions about your process. Do that, and you
could fall into the clutches of the “duck-rabbit” illusion shown
here:
If you fix your eyes solely on the duck, you’ll miss the
rabbit—and vice-versa.
If you're using
Minitab
Statistical Software for capability analysis, the
capability indices Cp and Cpk are good examples of... Continue Reading

I always knew I was different. Even as a kid.
“Is that me? Way out there in left field?” I asked the doc.
“Yes,” he nodded, as he looked at my chart. “I used brushing to
identify you on the graph.”
I wasn’t sure I liked getting brushed. It felt like my true
identify was being detected and displayed in a window for all to
see.
The doctor must have sensed my discomfort.
“It’s not uncommon—even for those... Continue Reading

Right
now I’m enjoying my daily dose of morning joe. As the steam rises
off the cup, the dark rich liquid triggers a powerful enzyme
cascade that jump-starts my brain and central nervous system,
delivering potent glints of perspicacity into the dark crevices of
my still-dormant consciousness.
Feels good, yeah! But is it good for me? Let’s see what the
studies say…
Drinking more than 4 cups of coffee... Continue Reading

If you’re not a statistician, looking through statistical output
can sometimes make you feel a bit like Alice in
Wonderland. Suddenly, you step into a fantastical world
where strange and mysterious phantasms appear out of nowhere.
For example, consider the T and P in your t-test results.
“Curiouser and curiouser!” you might exclaim, like Alice, as you
gaze at your output.
What are these values,... Continue Reading

"He looks just like his father...and
mother!"
Popular morphing sites online let you visualize the
hypothetical offspring of some very unlikely couples.
The baby of Albert Einstein and Kim Kardashian
(Kimbert?) would presumably look something like the image
shown at right.
What happens if you morph the features of two different
graphs?
For example, what would the baby of a time series plot and... Continue Reading