All Features
Davis Balestracci
Customer satisfaction surveys are all the rage these days. Healthcare has a couple of “800 pound gorilla” surveyors whose services (and nontrivial expense) have been pretty much forced upon it. In many cases, targets are set that are used to drive reimbursement.
A client once shared a 186-page…
Douglas C. Fair
Here’s a quick rundown of what we covered in part one of our list of top 10 mistakes to avoid when using statistical process control (SPC): training everyone, charting everything, segregating control charts from manufacturing, “pinching” the SPC coordinator, and using SPC because it’s a “good thing…
Douglas C. Fair
As you think about your organization’s manufacturing quality efforts—what you’ve overcome and what you hope to accomplish in the future—there is something you need to know.
You: What? Who? Me?
Me: Yes, you. No matter how long you’ve been playing this game (and I know many of you have been playing…
Minitab LLC
Anticipating challenges is always a daunting task for continuous improvement professionals. Unforeseen inefficiencies in process or defects in product development can throw timelines and associated costs into disarray. How to commit to realistic forecasts and timelines when resources are limited,…
Donald J. Wheeler
Last month we looked at what the empirical rule tells us about the data in a histogram. This month we will consider if there are any commonalities between different probability models that will allow us to make categorical statements without having to know the exact form of the probability model.…
Davis Balestracci
Because of a growing movement in the health insurance industry toward not reimbursing hospitals for any expenses caused by a system-acquired infection, one health system made efforts to improve its infection rate starting in the last quarter of 2016. In June 2017, a year-over-year graph was…
Larry Silverberg
Some 20 years ago, my colleague Chau Tran and I developed a way to simulate the trajectories of millions of basketballs on the computer.
We went to the coaches and assistant coaches at North Carolina State University, where we are based, and told them we had this uncommon ability to study…
Donald J. Wheeler
How can we use descriptive statistics to characterize our data? When I was teaching at the University of Tennessee I found a curious statement in a textbook that offered a practical answer to this question. This statement was labeled as “the Empirical Rule,” and it is the subject of what follows.…
Davis Balestracci
The Individuals chart is the “Swiss Army knife” of control charts. It usually approximates the supposedly “correct” chart under most conditions, and its use is much easier to understand and explain. It can also save you a major side trip into the swamp of unnecessary calculation minutiae,…
NIST
On February 14, 1929, gunmen working for Al Capone disguised themselves as police officers, entered the warehouse of a competing gang, and shot seven of their rivals dead. The St. Valentine’s Day Massacre is famous not only in the annals of gangland history, but also in the history of forensic…
Donald J. Wheeler, James Beagle III
Whenever we make a measurement, we have to decide how many digits to record. Traditional answers for this question are often little more than guesswork glorified by time. And with digital readouts, are all the displayed digits real? This column provides a sound and practical answer to these…
Andrew Hwang
National discussions of crucial importance to ordinary citizens—such as funding for scientific and medical research, bailouts of financial institutions, and revised tax laws—inevitably involve dollar figures in the millions, billions, and trillions. Unfortunately, math anxiety is widespread even…
Donald J. Wheeler, Geraint W. Jones
The precision to tolerance ratio is commonly used to characterize the usefulness of a measurement system. While this ratio is appealingly simple, it overstates the damage due to measurement error. In this paper we show how to compute honest precision to tolerance ratios that correctly describe…
Donald J. Wheeler
Capability ratios are widely used and sometimes misunderstood. The computer will gladly offer up values of each of the commonly used capability and performance indexes. Yet there is little appreciation of the inherent uncertainty contained in each of these numbers. Here we shall look at how to…
Mike Richman
Sustainable performance improvement is simply impossible without a firm handle on the precepts and tools of statistical process control (SPC). It is for this reason that we cover industrial statistics so frequently here at Quality Digest. After all, as the great Scottish physicist and engineer…
Bonnie Stone
Lean, also known as “lean manufacturing” or “lean production,” focuses on maximizing customer value by removing waste and eliminating defects. Lean tools are about understanding the process, looking for waste, preventing mistakes, and documenting what you did.
Let’s look at five lean tools used…
Eston Martz
Control charts take data about your process and plot it so you can distinguish between common-cause and special-cause variation. Knowing the difference is important because it permits you to address potential problems without over-controlling your process.
Control charts are fantastic for…
Scott A. Hindle, Donald J. Wheeler
In theory, a production process is always predictable. In practice, however, predictable operation is an achievement that has to be sustained, which is easier said than done. Predictable operation means that the process is doing the best that it can currently do—that it is operating with maximum…
Barbara A. Cleary
Taking time off for vacation seems to be a diminishing phenomenon among U.S. workers. Each year, Americans fail to use 662 million vacation days, and with those days $236 billion in economic opportunity is lost, according to the U.S. Travel Association.
Aside from the economic impact, there are…
Davis Balestracci
In my last column, I reflected back on my career to date and issued a challenge. Based on the relatively lukewarm response, let’s see whether I can engage a few more of you to join me on my quixotic journey.
“Trying to manage your career or your organization in a world changing as rapidly as ours…
Donald J. Wheeler, Rip Stauffer
How do extra detection rules work to increase the sensitivity of a process behavior chart? What types of signals do they detect? Which detection rules should be used, and when should they be used in practice? For the answers read on.
In 1931, Walter A. Shewhart gave us the primary detection rule…
John Flaig
Story update 9/26/2017: The words "distribution of" were inadvertently left out of the last sentence of the second paragraph.
Some practitioners think that if data from a process have a “bell-shaped” histogram, then the system is experiencing only common cause variation (i.e., random variation).…
Davis Balestracci
I have reached one of those life landmarks (receiving my Medicare card) and have been reflecting back... a lot. I will remain every bit as passionate about improvement and don’t think I will ever formally retire, but I also doubt I will have W. Edwards Deming’s tenacity to keep at it until I (…
Eston Martz
The Six Sigma quality improvement methodology has lasted for decades because it gets results. Companies in every country around the world, and in every industry, have used this logical, step-by-step method to improve the quality of their processes, products, and services. And they’ve saved…
Donald J. Wheeler, James Beagle III
Sometimes we use a chart for individual values and a moving range (an XmR chart) to assess the homogeneity of a finite data set. Since this is an "off-label" use for the XmR chart, we first consider the drawbacks associated with using a sequential technique as a one-time test, and then present an…