Blog posts and articles about tools and techniques that help keep Lean and Six Sigma projects on track.

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

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

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

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 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

In an earlier post, I shared an
overview of acceptance sampling, a method that lets you
evaluate a sample of items from a larger batch of products (for
instance, electronics components you've sourced from a new
supplier) and use that sample to decide whether or not you should
accept or reject the entire shipment.
There are two approaches to acceptance sampling. If you do it by
attributes, you... Continue Reading

Now that we've seen how easy it is to
create plans for acceptance sampling by variables, and to
compare different sampling plans, it's time to see how to
actually analyze the data you collect when you follow the sampling
plan.
If you'd like to follow along and you're not already using
Minitab, please download the free
30-day trial.
Collecting the Data for Acceptance Sampling by Variable
If you'll... Continue Reading

In my last post, I showed how to use Minitab Statistical
Software to
create an acceptance sampling plan by variables, using the
scenario of a an electronics company that receives monthly
shipments of LEDs that must have soldering leads that are at least
2 cm long. This time, we'll compare that plan with some other
possible options.
The variables sampling plan we came up with to verify the... Continue Reading

Earlier, I shared an
overview of acceptance sampling. Now we'll look at how to do
acceptance sampling by variables, facilitated by the tools in
Minitab Statistical Software. If you're not already using it
and you'd like to follow along, you can get the free
30-day trial version.
In contrast to acceptance
sampling by attributes, where inspectors make judgment calls about
defective items,... Continue Reading

If you're just getting started in the world of quality
improvement, or if you find yourself in a position where you
suddenly need to evaluate the quality of incoming or outgoing
products from your company, you may have encountered the term
"acceptance sampling." It's a statistical method for evaluating the
quality of a large batch of materials from a small sample of items,
which statistical
softwar... Continue Reading

Many
of us have data stored in a database or file that we need to
analyze on a regular basis. If you're in that situation and you're
using Minitab Statistical Software, here's how you can save some
time and effort by automating the process.
When you're finished, instead of using File > Query
Database (ODBC) each time you want to perform analysis on
the most up-to-date set of data, you can add a... Continue Reading

Not long ago, I couldn’t abide
statistics. I did respect
it, but in much the same way a
gazelle respects a lion. Most of my early experiences with
statistics indicated that close encounters resulted in pain, so I
avoided further contact whenever possible.
So how is it that today I write about statistics? That’s simple:
it merely required completely reinventing the way I thought about
and approached... Continue Reading

There are many reasons why a distribution might not be
normal/Gaussian. A non-normal pattern might be caused by several
distributions being mixed together, or by a drift in time, or by
one or several outliers, or by an asymmetrical behavior, some
out-of-control points, etc.
I recently collected the scores of three different teams (the
Blue team, the Yellow team and the Pink team) after a laser... Continue Reading

P-values are frequently misinterpreted, which causes many
problems. I won't rehash those
problems here here since my colleague Jim Frost has
detailed the issues involved at some length, but the fact remains
that the p-value will continue to be one of the most frequently
used tools for deciding if a result is statistically
significant.
You know the old saw about "Lies, damned lies, and... Continue Reading

Having delivered training courses on
capability analyses with Minitab, several times, I have noticed
that one question you can be absolutely sure will be asked, during
the course, is: What is the difference between the Cpk
and the Ppk indices?
Ppk vs. Cpk indices
The terms Cpk and Ppk are often confused,
so that when quality or process engineers refer to the
Cpk index, they often actually intend to... 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
variances.
Fortunately, I've had a lot more... Continue Reading

According
to this article published on Food Tank,
over 22 million pounds of food is wasted on college campuses each
year. Now that’s a lot of food waste!
Students all over the country are noticing excessive food waste
at their schools and are starting programs to bring awareness and
improve the problem. Naturally, many of these programs have roots
in Lean Six Sigma. In one example, a group of... Continue Reading

We
use statistics to arm ourselves with more information. That
information allows us to make more informed decisions. And the
sooner we can obtain this information, the better.
For example, suppose one of your manufacturing machines starts
to malfunction and makes your products out of spec. You don't want
to wait until the product reaches customers before you discover
this information. Then it's... 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