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Quality Scan: Six Sigma: A Dissenting Opinion

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By Vivek Sharma, CMfgE, CQE
Senior Member, SME
Manufacturing Engineer
MC Assembly
Melbourne, FL

Browse the business section of your local bookstore and you will see numerous hastily written books on Six Sigma. Anyone working in the business and manufacturing fields today has heard the term Six Sigma, it's the new mantra of quality, purported to solve all our problems.

This term is used by manufacturing plants and service organizations alike. It's applied to myriad processes such as machine control, order fulfillment, and even design projects. Companies like Motorola and GE swear by it, and numerous consulting outfits have sprung up offering their brand of Six-Sigma cures. The buzzword-loving quality field has a new king, but does the king have any clothes on?

Six Sigma was pioneered by Motorola in the 80s, and has evolved since then. Though there are many definitions of Six Sigma, it generally means to make fewer bad parts (about 3.4 in one million). Now, "making fewer bad parts" is a good idea, but it's hardly a revolutionary one, or even a new one, at that. The actual number of bad parts is a non-issue, but while we are shooting for a number, why not aim for zero bad parts, or more precisely the ZQC (Zero Quality Count) system invented by Shigeo Shingo of Toyota fame? Make "no bad parts" seems to be a better goal than saying, "make a couple of bad parts per million." Then again, if we keep saying per million, why not use the more familiar term "ppm" rather than the more pedantic-sounding 4.5 Sigma or Six Sigma. If a metric is required by manufacturing engineers, ppm is a more precise and widely used term, and conveys the message better than Six Sigma. Six Sigma is too subjective, cryptic, and hence open to different interpretations by different companies. For example, Motorola conveniently "un-accounts" for a 1.5 long-term drift, and still calls what they do Six Sigma, though it is closer to 4.5 Sigma.

One of the major ruses of the Six Sigma "institution" is that it pretends to be a crucial new quality tool, while in reality it has not introduced even one original tool to the quality field. If you peruse any Six-Sigma book or program, you will be hard-pressed to find a single new quality tool or statistical technique. In fact, Six Sigma uses old, well-established tools like SPC, DOE (Design of Experiments), QFD (Quality Function Deployment), Pareto analysis, etc., and just repackages them as Six Sigma.

The irony is that Six Sigma's cornerstone is SPC, but SPC uses Three Sigma limits in all its calculations! The truth is that Six Sigma does not have statistical techniques of its own, and just plagiarizes SPC.

Another area that Six Sigma espouses is DOE; but DOE was invented in the 1960s, and developed by people like Taguchi and the military. All of these approaches to quality improvement are effective techniques, but they are not new, and definitely were not invented by the Six Sigma institution. The credit for SPC, DOE, QFD, etc., should belong to the people who invented the techniques.

Another thing to remember about Six Sigma is that it will not fix your quality problems--and neither will any other quality tool--but it will help point you in the right direction. The same task can be accomplished by choosing fewer, but more appropriate, quality tools that are specific to the application and that can be employed at a much lower cost. Companies should be careful about getting caught in the Six-Sigma hype, over-analyzing their problems, and straying from common-sense decisions.

Smaller companies should especially be careful about jumping on the Six-Sigma bandwagon. The consultants and training can be quite expensive, and the results very generic. Sending employees to a statistics course at the local junior college will probably be as effective--and a whole lot cheaper. Do not get caught in the "numbers game," just stay the course with Continuous Improvement programs. Six Sigma has no new tools, and it just repackages the old ones. Brand marketing has come to the quality field; don't fall for the "new and improved" syndrome.


This article was first published in the October 2003 edition of Manufacturing Engineering magazine.