Tom Ehrenfeld: How do Six Sigma and Lean fit together? By Tom Ehrenfeld, author of The Startup Garden and A Leader’s Study Guide To The Gold Mine – Last updated: Sunday, April 4, 2010 – Save & Share – Leave a comment

How do Six Sigma and Lean fit together? Is one part of the other? Does one program cover more than the other? Or should the two not be compared in the first place? Please help define each of these programs, and explain how to think about both of them in the most productive way. Finally, elaborate on how whether other programs conflict or complement lean, and how to think about those as well.

Art Smalley Response:

I have witnessed plenty of Lean versus Six Sigma zealot arguments over the years at various client sites and at different conference settings. I think Tom is trying to stir the pot with this question Somehow I seem to manage to find a way to offend both camps with my standard responses which I will outline below.

I’ll start my answer however with an interesting side story. Back around the year 2000 I was part of an effort in McKinsey & Company to look at what Fortune 100 companies were using for improvement methodologies. At that time we estimated that 72 of the Fortune 100 companies were using some form of a corporate Six Sigma program to drive improvements. Far fewer were devout Lean companies at the time. A few years later many of these 72 companies had converted to “Lean Six Sigma” programs.

A couple of questions popped into my mind because of this study that I will try and tie back to Tom’s questions.  1) Why was Six Sigma so much more popular than Lean with the Fortune 100? 2) Why did so many Six Sigma companies eventually merge their programs to include Lean? 3) What was Lean lacking that Six Sigma offered? I had other questions but I will stop the list here for this post.

Six Sigma may have had its roots in an early program at Motorola but it was the success and exposure that it gained at General Electric which drove it to prominence around the world on both the managerial and technical side. GE is a highly successful and diversified company with a proven track record. Imitation is said to be the highest form of flattery so corporate leaders seeking to emulate Jack Welch and GE copied their improvement methods. In many ways I think the quantitative and specific process of Six Sigma is easier to understand than the fuzzy soft logic of lean (value stream, waste elimination focus, people oriented, etc.). I had an undeclared math minor and I took a heavy dose of statistics in college so that might just be my personal bias. Combine the success of GE, the more straight forward process of Six Sigma, the intuitive appeal of having highly trained Black Belts in the company, etc. and you have the recipe for a widely popular program.

So why did a lot of these programs eventually merge into becoming “Lean Six Sigma” practitioners for improvement? In my opinion both Six Sigma programs and Lean programs had significant gaps in them which caused them both to fall short of the Toyota Production System (which I maintain is different from the generic Lean programs in most companies). In short a marriage of convenience occurred between a lot of Lean and Six Sigma programs to address shortcomings inherent in both approaches at least as practiced at the time.

For example Six Sigma in its essence and most generic case addresses process variation and attempts to reduce it to an absolute minimum to achieve a high process capability and hence the Six Sigma level of defects or roughly 3.4 defects per million opportunities. (Note: I’ll ignore the 1.5 Sigma drift nuance and I will skip the realities of DMAIC versus DMADV and applications of Six Sigma to nontraditional processes or business model for simplicity in this article). Lean on the other hand seeks to question the nature of a process and eliminate it or the wastes associated with the process not just reduce the variation (Note: Likewise I’ll skip the Lean offshoots as well). The difference between reducing variation and eliminating waste is trivial but significant. Similarly Six Sigma in its generic form looks at a given process and studies it for improvement. Lean also does that but in the Western world more often than not Lean programs emphasize the flow of production across processes in an end to end fashion from raw materials to finished goods, etc.  Six Sigma was supposed to be about quality in its original form but it morphed into a more cost focused animal that seeks to generate financial benefits for the company. Lean from the beginning focused on a variety of things including cost, lead-time, inventory, productivity, safety, & morale.

In fairness I can point out benefits for Six Sigma and shortcomings of Lean as well. The Lean camp in the Western world at least seems to come off as math phobic in my opinion. Standardized Work is about as specific as they often get in terms of analyzing a process and that essentially boils down to time studying work elements, calculating takt time, and a few other things. Push them hard in terms of quality and eventually they mumble something about Poka-Yoke or Plan Do Check and Act (PDCA). In other words it is not a very rigorous quantitative approach. Six Sigma in comparison has a very specific vocabulary and structured way of approaching problems through Define, Measure, Analyze, Improve, and Control (DMAIC). Conversely I like to joke put three so-called Lean experts in the room and you’ll get at least three different opinions from each one on how to proceed.

I could go on and on but both camps have a few shortcomings that were especially evident to me a few years ago before so many programs merged to Lean Six Sigma. Why did this occur? Again I think the Six Sigma programs had some shortcomings and relied too much upon select black belts or green belts or master black belts, etc. to drive improvement. Joseph Juran and others have made similar and other criticisms. Most Lean programs on the other hand never figured out the “Jidoka” Pillar of the Toyota Production System. It remains a great mystery to me at least why the Lean movement only seems to care about flow, value, inventory, value stream mapping, 5S, and standardized work. In other words most Lean programs get the “Just in Time” pillar of TPS but remain woefully ignorant of the “Jidoka” pillar (build in quality and separate man from machine). I was an engineer in an engine plant which was Taiichi Ohno’s model plant for TPS. We did design of experiment style problem solving, conducted process capability studies, implemented gage R&R studies and other quantitative activities. You don’t get to the low ppm numbers (0 to 50 range) that most Toyota plants can boast about at the production line level without these actions up front and during production.

So in the end the Lean Six Sigma marriage in the western world might not be such a bad thing. If Six Sigma can approach the missing Jidoka pillar of TPS (and add more of course) then that will shore up one of the weaknesses in modern Lean programs I observe. Six Sigma practitioners can also bring some needed quantification skill and objectivity to Lean camps that often rely upon “gut feel” or “let’s do what my sensei told me last week”. Conversely the Lean lens can also help alleviate some of the weaknesses inherent in traditional Six Sigma programs mentioned above. In the end whatever flavor of Lean or Six Sigma gets implemented they all have to answer the same basic questions. How do you satisfy the customer and make a profit? How do you continuously improve and outpace the competition in terms of products and process improvements? How do you develop employees and create a safe engaging work atmosphere? Customers and economics in the end will judge companies more upon results than methods.