All Features
Donald J. Wheeler
Define, measure, analyze, improve, control, goes the mantra used to carry out improvement projects in many companies. In various books, these steps get slightly different interpretations. But the overall outline is still characterized by DMAIC. This article will show a proven way to simplify and…
Quality Digest, Donald J. Wheeler
Dr. Donald J. Wheeler has been one of Quality Digest’s most highly read authors for decades. His teaching on the use of control charts in industrial settings has long been considered the gold standard. He has conducted more than 1,100 seminars in 17 countries on six continents, and his books have…
Donald J. Wheeler
Outliers are values that don’t “fit in” with the rest of the data. These extreme values are commonly considered a nuisance when we seek to summarize the data with our descriptive statistics. This article will show how to turn these nuisances into useful information.
The earliest statistical tests…
Hannah Fischer-Lauder
In an age where data are among the most valuable assets for any business, the ability to retrieve, process, and utilize information efficiently is critical for success. Yet traditional data-retrieval methods often struggle with the demands of today’s dynamic business environments. Enter retrieval-…
Donald J. Wheeler
The Man of La Mancha never got to the unreachable goal—and if you’re being judged by overall equipment effectiveness (OEE), then your manager may also be dreaming an impossible dream. This column will look at problems associated with the use of OEE values.
OEE is a value often used in lean…
Donald J. Wheeler
In last month’s article, “ANOVA and the Process Behavior Chart,” we saw how both techniques use the same basic comparison to answer completely different questions. Here, we’ll look at a case history where both techniques were used.
A physical property of a mass-produced item was important to its…
William A. Levinson
Recent labor relations controversies and ongoing arguments about the minimum wage have raised questions as to how a supply chain should share the utility it produces.
If we ask the wrong question, however, we’ll get the wrong answer. “What is a fair share?” asks how a supply chain should divide a…
Donald J. Wheeler
When Sir Ronald Fisher created the analysis of variance (ANOVA) in the 1920s, he extended the two-sample t-test to allow the comparison of k sample averages. During the same time period, Dr. Walter Shewhart was creating the process behavior chart. So it should be no surprise that both techniques…
Donald J. Wheeler
Managers are commonly fed a diet of report-card data. These data have usually been aggregated into summaries, averages, and totals to characterize the big picture. As useful as such summaries can be, they can also be an obstacle to an effective analysis. Here, we’ll learn how to avoid this obstacle…
Gabriel Popkin
Time: We all have a sense of it, an innate feel for it. We see it and use it every day. If you’re like me, the first thing you do in the morning is check the time on your phone to see if you need to get out of bed or if you can close your eyes and catch a few more z’s.
Once you’re up and moving,…
Donald J. Wheeler
An engineer once told me, “I work on project teams that have an average half-life of two weeks, implementing solutions with an average half-life of two weeks.” Time after time, and in place after place, our improvement efforts often fall short of expectations and fade away. In this article, I will…
Gleb Tsipursky
The 2024 U.S. presidential election is shaping up to be one of the closest in recent history, with Kamala Harris and Donald Trump locked in a dead heat in many polls. This razor-thin margin amplifies the effect of even small demographic changes, such as those driven by the recent surge in remote…
William A. Levinson
Most quality practitioners are familiar with the Taguchi loss function, which contends that the cost of any deviation from the nominal follows a quadratic model. This is in contrast to the traditional goalpost model, where anything inside the specification limits is good, and anything outside them…
Donald J. Wheeler
The objective of all improvement projects should be to improve the overall process. Everything else should be secondary to this objective. If you improve the efficiency of a support process, or even a portion of the core process, but at the same time lower the efficiency of the overall process,…
Harish Jose
Recently, I wrote about the process capability index and tolerance interval. Here, I’m writing about the relationship between the process capability index and sigma. The sigma number here relates to how many standard deviations the process window can hold.
A +/– 3 sigma contains 99.73% of the…
Donald J. Wheeler
The four common capability and performance indexes collectively contain all of the summary information about process predictability, process conformity, and process aim that can be expressed numerically. As a result, any additional capability measures that your software may provide can only…
Donald J. Wheeler
In May 1924, Walter Shewhart wrote a memo that contained the first example of a process behavior chart (i.e., a “control chart”). It was a chart for individual values that would be known today as a p-chart. Shewhart’s insight was that “three-sigma” limits will filter out virtually all of the…
Scott A. Hindle
Walter A. Shewhart is lauded as the Father of Statistical Process Control (SPC) and is perhaps best remembered for the SPC control chart. The first record of Shewhart’s control chart is found in a Bell Telephone Laboratories internal memo from May 16, 1924, making today the 100th anniversary of…
Donald J. Wheeler
One hundred years ago this month, Walter Shewhart wrote a memo that contained the first process behavior chart. In recognition of this centennial, this column reviews four different applications of the techniques that grew out of that memo.
The first principle for interpreting data is that no data…
Douglas C. Fair, Scott A. Hindle
In less than two months we will celebrate the 100th anniversary of the invention of the control chart, a tool most often associated with statistical process control (SPC). Considering SPC from our modern perspective made us ask, “Is SPC still relevant?”
It’s a question asked within the purview of…
Donald J. Wheeler
When presented with a collection of data from operations or production, many will start their analysis by computing descriptive statistics and fitting a probability model to the data. But before you do this, there’s an easy test that you need to perform.
This test will quantify the chances that…
Donald J. Wheeler
Over the past two months we’ve considered the properties of lognormal and gamma probability models. Both of these families contain the normal distribution as a limit. To complete our survey of widely used probability models, this column will look at Weibull distributions, a family that doesn’t…
Donald J. Wheeler
Clear thinking and simplicity of analysis require concise, clear, and correct notions about probability models and how to use them. Here, we’ll examine the basic properties of the family of gamma and chi-square distributions that play major roles in the development of statistical techniques. An…
Scott A. Hindle, Douglas C. Fair
So far in this series our focus has remained on statistical process control (SPC) in manufacturing. We’ve alternated between more traditional uses of SPC that remain relevant in this digital era and discussing uses of SPC and its related techniques that are enabled by the marvels of modern…
Donald J. Wheeler
When do we need to fit a lognormal distribution to our skewed histograms? This article considers the basic properties of the lognormal family of distributions and reveals some interesting and time-saving characteristics that are useful when analyzing data.
The lognormal family of distributions…
