As we saw on Part I, there are some fundamentally flawed conceptual problems with Six Sigma and its statistical underpinnings are shaky indeed.But the aspect of Six Sigma that makes it that makes it least useful as a tool to improve competitiveness is that it is based on defect detection and elimination (reduction) and not improvement.Removing the defects from a process does not improve it. It merely allows it to operate the way it was intended to operate. It is somewhat counterintuitive, but one cannot improve a process by reacting to its outcome. That is what Deming is saying in the 3rd of his 14 points, “Cease dependence on inspection as a means to improve quality.”Of course removing defects is desirable. And if there are a lot of defects, rework, scrap, etc., eliminating it will be all to the good, but that doesn’t change the fundamental operation of the process. In order to do that, one must concentrate efforts on working upstream.Over the years in consulting I have always differentiated between two types of variables. Those that are process outcomes; what the customer sees. I call these Key Quality Characteristics. Upstream are the variables that, in some combined and interactive way produce those results. I call these Fundamental Process Variables.For example, a key quality characteristic of a magnetic disk for a disk drive might be it’s flatness. In today’s demanding environment, recording disks must be extremely flat. The customer demands it. But disk flatness is a result of a machining process. In that sense it is an outcome. To make a disk more flat it is necessary to understand the variables of the upstream process that govern flatness; the grinding pressure, the abrasive particle size of the grinding slurry, etc.Detecting disks that aren’t flat (defects) does not make disks flatter. To improve disk flatness requires action on the fundamental process variables.This seemingly semantic difference may seem trivial, but on the contrary, it drives improvement efforts and ultimately determines the level of competitiveness a company can attain. Many companies execute well, but there’s more to competitiveness than that.Again we can look to Deming for the fundamental message. One of my favorite quotes of his is, “It’s all very simple, really, pay attention to quality in the right way, costs will go down and you enter the market with the best quality at the lowest cost. You will capture the market.” This is from an interview he gave to the New York Times many years ago. It is also from the message he brought to Japan in 1950. It is as true today as it was then, the difference being that today there is no doubt that it is true.Next is Part III - How the approach to improvement determines competitiveness.
Six Sigma Part II
June 23rd, 2008 | Deming, Scientific Thinking, Statistical Thinking
5 comments ↓
Your animosity toward Six Sigma is impacting your credibility … and thinking. Six Sigma addresses “variation” and not defects. Defects are a key performance indicator. The variation reduction is typically done through a form of root cause failure analysis. Variation is usually identified through tools like statistical process control and control charts. Neither of these rely on final inspection and are at the heart of Deming’s 3rd point. Contrary to your assertion, the entire chain of events does in fact fundamentally improve the process.
To paraphrase, all improvement tools are flawed. Some have few enough flaws to allow them to be useful. A good continuous improvement professional is knowledgeable regarding a multitude of tools and applies them only where they make sense.
Thanks for your comment.
I have no animosity to ideas or methods. So your characterization of me, in addition to being of the nature of a personal attack, is simply untrue. Elsewhere you suggest, by inference, that I am not a good ‘continuous improvement professional’. That’s a little condescending. Why all the animus? It’s only an idea.
As you point out at the end of your comment, some methods work better than others. It is also true that some methods are theoretically flawed and some are not. It is the point of these posts to point out that Six Sigma, despite its wide acclaim, has deep theoretical flaws and doesn’t work very well. Both these assertions can be demonstrated.
As for the specific point you raise, the heart of Deming’s point 3 is not to move inspection upstream. It is, if you read it, a call to stop depending on the analysis of outcomes to improve. That point seems to have been missed by you, although it was the main point I was trying to make in this second part of the Six Sigma posts.
It is a general point and not aimed at Six Sigma specifically. I included it in this discussion because it is germane. Defects are outcomes. You can’t improve a process by reacting to its outcomes.
As for root cause analysis, that is just a more dliigent way to chase defects. Moreover, if you believe that processes are systems, then there is no such thing as a ‘root cause’. It can only be defined subjectively.
You seem to have to the mistaken idea that if one wants to improve, one will improve. I wish it were that simple. But one must also have knowledge about what to do. Otherwise you can (and people do) make things worse.
Again thanks for your comment. I think it’s possible to have this discussion without characterizing the other people involved.
A number of interesting points, in both the original post and the discussion. Your discussion of Key Quality Characteristics and Fundamental Process Variables touches on the risk, when working to improve process outcomes (the dependent variable) that the improvement efforts will be myopic, overlooking other process outcomes and making them worse…also known as local suboptimization. I believe that one of the strengths of Six Sigma is the way that it attempts to mitigate this risk by requiring that all improvements have verified impacts on the corporate bottom-line.
I believe that Deming would have preferred that practitioners develop a deeper understanding of the process they are trying to improve and any impacted processes in the system, so as not to overlook any key outcomes or variables. However, being able to trace a single process outcome to the business bottom line requires developing a deeper understanding of the entire business value chain, an effort that I think Deming would have approved of.
John,
I would agree with you if Six Sigma was simply an effort to move inspection upstream to the earliest opportunity to detect a defect in order to eliminate the possibility of adding further value to something of no value. Fortunately, that is NOT what a good implementation of Six Sigma does and that is why I respectfully disagree with you and agree with Mike’s earlier comments. In my own situation, I’ve used the Six Sigma process to bring about improvements to the bottom line by changing the labor content of an assembly and by finding an improved process that takes longer (more labor) than the orginal, but achieve’s such a dramatic yield improvement that it more than recovers the cost of the added labor. Admittedly, I do not strictly use Six Sigma all of the time - it is a long and involved process, but when I have a problem with no clear, “just do it” solution you can bet I’ll turn to the Six Sigma process and dig in.
Hi John,
I think one key word idea in your comment is “…good implementation of six sigma..” There is, of course, variation in how Six Sigma is defined and carried out.
It is also true that a planned approach to improvement efforts is better than some helter skelter arrangement.
But planned approach to improvement, good implementation, top management support, etc., are not the exclusive domain of Six Sigma. In 1950 Deming told the management of Japan’s industry that they had to be in the leadership. Nothing new about that.
As for dramatic yield improvement, it happens. I have seen it many times and often before there was such a thing as Six Sigma. Again, there is nothing particularly Six Sigma about that, not is it particularly new.
Another example is the DMAIC methodology. In one form or another it’s been around for years.
As I pointed out in another post, I have advocated the use of in-house, specially trained resources to guide improvement efforts. I didn’t name the role after Karate belts, I called them statistical quality consultants, but it’s basically the same idea. I was advocating that to clients in 1980. Six years before Six Sigma hit the scene.
In an article I wrote for an Australian Business Journal, I called Six Sigma, largely a matter of the “…same soup in a different can…” Six sigma has basically changed a lot of terminology, added some statistical smoke and mirrors and other than that is not terribly different from the traditional ASQ approach to quality. That is why it has been so completely embraced. It’s nothing really new. It is a defect oriented program. Set the spec, find the defect via inspection, segragate the defect, find the “root cause” (is if there were such a thing) and take corrective action. In part III I point out why that falls short in my opinion.
Other than that what is unique to Six Sigma is the statistical part of it and that is also what I criticized. It is theoretically unsound and I don’t think that there is much argument with that….at least not among statisticians.
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