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

In my last post, I discussed how a DOE was
chosen to optimize a chemical-mechanical polishing process in
the microelectronics industry. This important process improved the
plant's final manufacturing yields. We selected an experimental
design that let us study the effects of six process parameters in
16 runs.
Analyzing the Design
Now we'll examine the analysis of the DOE results after the
actual... Continue Reading

I used to work
in the manufacturing industry. Some processes were so complex that
even a very experienced and competent engineer would not
necessarily know how to identify the best settings for the
manufacturing equipment.
You could make a guess using a general idea of what should be
done regarding the optimal settings, but that was not sufficient.
You need very precise indications of the correct... Continue Reading

P values have been around for nearly a century and they’ve been
the subject of criticism since their origins. In recent years, the
debate over P values has risen to a fever pitch. In particular,
there are serious fears that P values are misused to such an extent
that it has actually damaged science.
In March 2016, spurred on by the growing concerns, the American
Statistical Association (ASA) did... Continue Reading

Like so many of us, I try to stay healthy by watching my weight.
I thought it might be interesting to apply some statistical
thinking to the idea of maintaining a healthy weight, and the
central limit theorem could provide some particularly useful
insights. I’ll start by making some simple (maybe even simplistic)
assumptions about calorie intake and expenditure, and see where
those lead. And then... Continue Reading

After my husband’s most recent visit to the dentist, he returned
home cavity-free...and with a $150 electric toothbrush in
hand.
I wanted details.
It began innocently. His dreaded trip to the dentist ended in
high praise for no cavities and only a warning to floss more. That
prompted my programming-and-automation-obsessed husband, still in
the chair, to exclaim, "I wish there was a way to automate... 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
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