Choosing the right type of subgroup in a control chart is
crucial. In a rational subgroup, the variability within a subgroup
should encompass common causes, random, short-term variability and
represent “normal,” “typical,” natural process variations, whereas
differences between subgroups are useful to detect drifts in
variability over time (due to “special” or “assignable” causes).
Variation within... Continue Reading
Parts 1 and
2 of Gauging Gage we looked at the numbers of parts, operators,
and replicates used in a Gage R&R Study and how accurately we
could estimate %Contribution based on the choice for each. In
doing so, I hoped to provide you with valuable and interesting
information, but mostly I hoped to make you like me. I mean
like me so much that if I told you that you were doing... Continue Reading
You run a capability analysis
and your Cpk is bad. Now what?
First, let’s start by defining
what “bad” is. In simple terms, the smaller the Cpk, the more
defects you have. So the larger your Cpk is, the
practitioners use a Cpk of 1.33 as the gold standard, so we’ll
treat that as the gold standard here, too.
Suppose we collect some data and run a capability analysis using
In Part 1 of Gauging Gage, I looked at how adequate a
sampling of 10 parts is for a Gage R&R Study and providing
some advice based on the results.
Now I want to turn my attention to the other two factors in the
standard Gage experiment: 3 operators and 2 replicates.
Specifically, what if instead of increasing the number of parts in
the experiment (my previous post demonstrated you would need... Continue Reading
"You take 10 parts and have 3 operators measure each 2
This standard approach to a Gage R&R experiment is so
common, so accepted, so ubiquitous that few people ever question
whether it is effective. Obviously one could look at whether
3 is an adequate number of operators or 2 an adequate number of
replicates, but in this first of a series of posts about
"Gauging Gage," I want to look at... 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
The ultimate goal of most quality improvement projects is clear:
reducing the number of defects, improving a response, or making a
change that benefits your customers.
We often want to jump right in and start gathering and analyzing
data so we can solve the problems. Checking your measurement
systems first, with methods like attribute agreement analysis or
Gage R&R, may seem like a needless waste... Continue Reading
There may be huge potential benefits waiting in the data in your
servers. These data may be used for many different purposes. Better
data allows better decisions, of course. Banks, insurance firms,
and telecom companies already own a large amount of data about
their customers. These resources are useful for building a more
personal relationship with each customer.
Some organizations already use... Continue Reading
You need to consider many factors when you’re buying a used car.
Once you narrow your choice down to a particular car model, you can
get a wealth of information about individual cars on the market
through the Internet. How do you navigate through it all to find
the best deal? By analyzing the data you have available.
Let's look at how this works using
the Assistant in Minitab Statistical... 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,
Whatever industry you're in, you're going to need to buy
supplies. If you're a printer, you'll need to purchase inks,
various types of printing equipment, and paper. If you're in
manufacturing, you'll need to obtain parts that you don't make
But how do you know you're making the right choice when you have
multiple suppliers vying to fulfill your orders? How can you
be sure you're... Continue Reading
by Erwin Gijzen, Guest
People who work in quality improvement know that the root causes
of quality issues are hard to find. A typical production process
can contain hundreds of potential causes. Additionally, companies
often produce products with multiple quality requirements, such as
dimensions, surface appearance, and impact resistance.
With so many variables, it’s no wonder many companies... Continue Reading
Cp and Cpk are well known capability indices commonly
used to ensure that a process spread is as small as possible
compared to the tolerance interval (Cp), or that it stays well
within specifications (Cpk).
Yet another type of capability index exists: the Cpm, which is
much less known and used less frequently. The main difference
between the Cpm and the other capability indices is that the... Continue Reading
In technical support, we frequently receive calls from Minitab
users who have questions about the differences between Cpk and
Michelle Paret already wrote a great post about the
differences between Cpk and Ppk, but it also helps to have a
better understanding of the math behind these numbers. So in this
post I will show you how to calculate Ppk using Minitab’s default
settings when the... Continue Reading
Suppose that you plan to source a substantial amount of parts or
subcomponents from a new supplier. To ensure that their quality
level is acceptable to you, you might want to assess the capability
and Cpk indices) of their manufacturing processes and check
whether their critical process parameters are fully under control
control charts). If you are not sure about the efficiency... Continue Reading
Keeping your vehicle fueled up is expensive. Maximizing the
miles you get per gallon of fuel saves money and helps the
But knowing if you're getting good mileage requires some data
analysis, which gives us a good opportunity to apply one of the
common tools used in Six Sigma -- the I-MR (individuals and moving
range) control chart to daily life.
Finding Trends or Unusual... Continue Reading
previous posts, I’ve outlined some reasons why
a Lean Six Sigma project might have been deemed a failure. We’ve
gathered many of these reasons from surveying and talking with our
I’d like to present a few more reasons why projects might fail,
and then share some “words of wisdom” from Minitab trainers on how
you can avoid these project failures.
Forcing Projects into DMAIC
Certain... Continue Reading
by Matthew Barsalou, guest blogger
The field of statistics has a long history and many people have made contributions over
the years. Many contributors to the field were educated as
statisticians, such as Karl Pearson and his son Egon Pearson. Others were people with problems that needed
solving, and they developed statistical methods to solve these
The Standard Normal Distribution
One... Continue Reading
by Dan Wolfe, guest blogger
How would you measure a hole that was allowed to vary one tenth
the size of a human hair? What if the warmth from holding the part
in your hand could take the measurement from good to bad? These are
the types of problems that must be dealt with when measuring at the
As a Six Sigma professional, that was the challenge I was given
when Tenneco entered into... Continue Reading
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