Six Sigma–Sporadic vs. Persistent Problems


In the eighth chapter of their book Six Sigma:  The Breakthrough Strategy Revolutionizing the World’s Top Corporations, the authors Mikel Harry, Ph.D., and Richard Schroeder discuss “Measuring Performance on the Sigma Scale.”   In the previous chapter, the authors discussed the Breakthrough Strategy of implementing Six Sigma on the business, operational, and process level.

In this chapter they focus on the question “how does improving the Sigma level of a company’s processes improve that company’s performance?”   And when I say “improve that company’s performance”, I am referring to the company’s performance on the business, operational, and process level.

The first topic in the chapter is a discussion of sporadic vs. persistent problems.   It should be pretty clear what these are:  they refer to how often the problems occur.    However, in examining further those problems which occur “constantly” as opposed to “once and a while”, you also may find that you are examining the very nature of the problem.   A sporadic problem is one that the company focuses on first, for the obvious reason that it stands out among the background.  A problem that occurs constantly, however, may be invisible just because it happens all the time.

Six Sigma, due to its statistical toolkit, is especially adapt at teasing out the persistent problems and solving them, thereby reducing the overall defect rate.  Here are some reasons given for persistent defects:

  • hidden design flaws
  • inadequate tolerances
  • inferior processes
  • poor vendor quality
  • lack of employee training
  • inadequate tool maintenance
  • employee carelessness
  • insufficient inspection feedback

The problems that management may have with regards to persistent defects are that a) they may not even be aware that hidden persistent problems exist, and b) if they are made aware of them, they may assume that correcting these problems is uneconomical.    This perception can be changed if management can be shown the costs of these persistent defects, and that these costs are greater than the costs of correcting them.

The real reason why a company needed to get rid of persistent defects is that, the authors liken it to a cancer that spreads.  A persistent defect does not only persist, it spreads throughout an otherwise healthy company.   It’s best to target this cancer with the laser-like precision of Six Sigma so that a company can truly do the best work that can be done.

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