Friday, March 13, 2009

More Prevaricating about Sigma

The one anonymous comment I received the other day after my initial posting seemed to imply that I am somehow against Six Sigma. Nothing could be further from the truth. I am currently a Quality consultant, and a large part of my business has been (and continues to be) Six Sigma. My background goes beyond Six Sigma, though, and I do have some reservations about some of the common practices within Six Sigma.
Before I ever heard of Six Sigma, I was heavily involved in the Navy’s Total Quality Leadership initiative. I had studied all the quality gurus, consulted and written courses in Statistical Process Control and systems approaches to process improvement, taken a masters degree in Quality and applied statistics. I had been director of quality for a large overseas base and an internal consultant to the entire Department of the Navy.
From the viewpoint of statistical methods, I initially viewed Six Sigma with some suspicion. There was the matter of the “1.5 Sigma Shift” applied blindly to all the calculations. This is just For one thing, one of the first slides in the deck, in the first presentation I saw, was a direct copy of one I had seen at a Crosby presentation. It talked about what you might get in “a three-sigma world,” and listed the usual “Babies dropped on heads” and “Airplane crashes,” etc. This is a great marketing slide, especially when coupled with the one that inevitably follows it, showing the several-order-of-magnitude improvement in “a six-sigma world.” The Crosby presentation, of course, followed the initial slide with a slide showing the improvement in a “zero-defects world.”
This slide is a pretty persuasive slide. It deals with errors that we would, of course, want to get as close to zero as possible. We can’t tolerate any aircraft falling from the sky, and can’t tolerate any babies being dropped on their heads, so of course three sigma (Cpk = 1) is never going to be as good as six sigma (Cpk = 2), but it’s somewhat disingenuous, for a number of reasons:
The calculations are correct, unless you are using the common “1.5-Sigma Shift,” in which case the six-sigma world calculations are too pessimistic (more on the shift later).
The idea of three sigma and six sigma come from the world of Statistical Process Control (SPC) and Capability Studies for continuous data, where you have tolerance limits (usually two-sided), around a process average. The data in the slide are for errors, countable things, discrete data, and all the examples are about the types of errors where the only acceptable tolerance limit is the lower bound of zero. Normal distribution theory doesn’t usually apply in this situation.
I’ve never understood why three sigma was the starting point for these slides, but I’ve always suspected that it was to promote the misconception that SPC somehow “stops” at three sigma (because of the three-sigma control limits used in SPC), and so the other approaches touted in the second slide are superior. Nothing could be further from the truth; if you watch or read “The Japanese Control Chart” by Don Wheeler, you’ll see a Japanese company that gets to TWELVE sigma, just using a paper control chart.
So I don’t really like that slide, but it worked OK as a marketing tool. From the viewpoint of statistics, I worried mostly about the mixing of the methods used to assess DPMO (Defects per Million Opportunities) and the 1.5-sigma shift. An excellent paper by Roger Hoerl got me over that. He pointed out that traditional views of capability left out the idea of mistakes or defects, and made a strong case for a metric like DPMO that can translate the idea of capability across distributions.
The “1.5 Sigma Shift” is another can of worms, but not for statisticians. Put simply, statisticians pay very little attention to it. It’s just a transformation that we will probably all be stuck with until someone with enough credibility to stop a flawed practice yells “STOP!” It’s relatively harmless, anyway, and it works as a “fudge factor” or a safety factor so you generally end up beating expectations. While it is true that undetected shifts in even a well-controlled process might allow for a lot of closer-to-spec product to be produced over many days, that does not justify an arbitrary value of 1.5 sigma to be universally applied. There are a lot of reasons for this…we’ll get into it another time.

Wednesday, March 11, 2009

A Rookie's First Blog

Welcome to my new Blog! As a new blogger, I thought I’d take the time to talk in this first post about my vision for this blog. My intention is to provoke thought-provoking, open discussion on all aspects of enterprise improvement, operational excellence, continual improvement, “Big-Q” quality, Six Sigma, Lean, “Lean Six Sigma,” or whatever label you wish to use for a systemic approach to optimizing the performance of your organization for all its stakeholders.
It might seem odd that I don’t pin anything down with a label. Although I consider myself a Quality Consultant, I have recognized that over the past 20 years many of my fellow consultants have split improvement consulting into ever-smaller competitive niches. While there is much to be said for specialization and developing depth in a particular knowledge area, there is very little to be said for promoting that one area as “the” fix to a complex system. I have seen presenters at Quality conferences tout Lean over Six Sigma, Six Sigma over Lean, DMADV over DMAIC, “Lean Six Sigma” over everything else…it’s harmful to all of us, and harmful to all our clients, and it needs to stop. Now.
When he was alive, people at Deming seminars used to ask why Dr. Deming, with all his knowledge, didn’t provide specific prescriptions and methodologies. Quality professionals tended to study not only Deming, but Juran, Crosby, Kano, Ohno, Shingo and many others (i.e., Ackoff and Senge for Systems Theory, Kohn and Maslow for psychology, Lewis and Peirce for epistemology). Good quality practitioners were expected to know project management, standardization, lean (as they came to be called) tools, Cost-of-poor-quality, SPC, QFD, “seven old tools,” “seven new tools,” statistical theory, and systems theory.
Having said all that, there was a lot of variation in the Quality world. Some people followed their Gurus and only studied the others to find targets for disdain. Some became very dogmatic. Deming said that “the most important numbers are unknown and unknowable” so some people took that to mean that you don’t worry about costs, even those that are knowable. Some decided that they could act as curmudgeonly and arrogant as the Gurus themselves. These things (and more) turned many executives off.
After Deming died, consultants found that very few hiring executives cared much for philosophical approaches. Some of this reluctance could be laid on some of the consultants themselves; some of the most dogmatic “Deming Disciples” spent much of their time quoting Deming, often arguing about “what Dr. Deming said” or “what Dr. Deming meant” like biblical scholars interpreting a prophet.
I think, though, that managers just didn’t want to deal on a conceptual basis…nothing in business school had prepared them for seeing the long view or managing a system. They just wanted simple methods they could install quickly and painlessly. Six Sigma seemed in many ways to fit that bill. It was proven at GE, Motorola, and Allied Signal. It was trainable, had a defined roadmap, a hierarchical structure that could (with a reasonably small amount of pain) be bolted on to existing structures. Importantly, it could be positioned as a cost-cutting initiative rather than a quality initiative.
In the beginning, it fell to Quality professionals to develop the initial Six Sigma training materials. Black Belts were trained, who became Master Black Belts, and trained other Black Belts, who became Master Black Belts, etc. Because many of those Black Belts had had little or no previous exposure to Quality concepts and principles, their understanding of the tools suffered. They passed their subset of knowledge on to others, and more concepts and tools were lost in each generation…classic “rule four of the funnel.”
Management, too, fell victim to the dilution. Busy executives became too busy to take the time to learn enough to effectively lead Six Sigma as a strategic initiative, and upper/middle managers became too busy to take a few days to learn to be an effective champion. Process owners received little or no training to help them understand and cope with the changes and resource needs. Project selection became less strategic, sometimes devolving into Black Belts looking for their own projects and trying to find their own project champions. Some of these Black Belts ended up laid off; they sometimes found work with consulting companies.
As the focus narrowed from optimizing systems to local improvements and cutting costs, much of the rigor was diluted, and the conceptual underpinnings were often cut or minimized in the training. Deming’s fourteen points, seven deadly diseases and System of Profound Knowledge were treated as an important historical footnote…maybe included in introductory material, maybe not. Because Black Belts were not trained in simpler, non-project or small-project approaches, and all responsibility for tools rested with the Black Belts, many opportunities for process standardization & control, continual improvement, and reduction of waste were missed.
The Toyota Production System (Americanized to “Lean Manufacturing”) came in to help fill some of the gaps in Quality Management Systems. Because lean provides a relatively simple set of tools for daily management and doesn’t require much statistical knowledge, it quickly caught on. In some organizations, it was seamlessly integrated into an overall quality system; in others, it became another flavor of the month, replacing Six Sigma. In others, the boardroom decided to let Six Sigma and Lean compete for viability. Some consulting companies began selling “Lean Six Sigma.” Even simpler approaches, like Shop Floor Standardization, were lost in many organizations.
I could go on, but it’s already been a long path to get to an explanation of why I don’t call this a “Six Sigma” blog or a “Lean” blog, or even a “Lean Six Sigma” blog, even though I hope and fully expect to be discussing all these topics in depth and detail, as time goes on. What I’m going for is the kind of reasoned and mostly respectful discourse we used to have in the Deming Electronic Network. Hopefully, we can all suspend our assumptions, bring our knowledge to the table, learn and have fun!