What is the question?

Is this question why you have defects? Is the question how many are there? Why do you want to know that?

You have, perhaps inadvertantly, found one of the basic weakenesses of the six-sigma approach. What a defect is and what the area of opportunity is are both arbitrarily defined and one can make a report look better or worse by changing the definition.

But that is just a game.

I assume you wish to eliminate/reduce errors.

Where do they come from? Is there a stable pattern of errors (statistical control chart). If there is not a stable pattern when are the peak occurrences? If there is a stable pattern, then something systemic must be changed.

You list a lot of tools, but no questions. It is hard to know which tool makes the most sense if one doesn’t know what question he or she is trying to answer.

Thanks for your reply

I need six sigma for finding defects in a web application and to find the solution on how to reduce the defects.
I have two main questions require answers.

Question 1

I have used DPMO for
calculation the defects in given opportunity
For Root Cause analysis i made
use of Pareto Analysis.
These two were not sufficient for web applications.
Is there any other methods i can use for
1)Calculating defects
2)Root Cause Analyzing tool

Question 2
1)Can i use sampling methods(Random,Convenient,Purposive)
If so which is best suited.
2)For analyzing data can i use any tools(Chi-square,Percentage Analysis)

It will be really helpful if u could answer the above questions.
Even if your answers give me an idea of these,it will be useful.

Thanks in Advance
Lavanya

I am new to Six sigma.
Am currently working in a software project which requires six sigma concepts.
For determining quality of a software product
I have used DMPO .
Is there any other concepts for determining the
quality of a software product.
Can i use any statistical tool ?
Please advice..
Thanks
Lavanya

Yes, I’d say you have a better idea of the problems with some uses of sigma and cpk than most. In my experience, showing process stability before reporting cpk (Six Sigma efforts or not) is the exception and not the rule.

Also I think you are right to point out that it is easy to let the perfect be the enemy of the good. Clearly if some organization is paying no attention to quality and not quantifying data and they adopt a Six Sigma mehtodology (or almost anything like it) they’ll see improvments and be better off.

It is just frustrating to see a very effective and time-proven set of techniques like those Toyota has been using since Taiichi Ohno worked there, be ignored for an ineffective and theoretically flawed method.

Especially now that we have some years to look at what Six Sigma has done for some its strongest proponents, we can see it has not come even close to helping those companies and Toyota, Honda, etc. just keep rolling over everything in sight.

I will just add a clarification. As you point out, there are excellent alternative improvement methodologies. I meant that there are few practical alternatives for introducing and building statistical and scientific thinking across an organization. I believe that this is a valuable goal, beyond Six Sigma’s efficacy as an improvement methodology. In my experience, Six Sigma offers training and implementation of statistical and scientific thinking that most people, from senior managers to line employees across the organization, can comfortably swallow.

3.4 dpmo is just too laughable for anyone with an once of common sense to take seriously. It was first based on a “drift” then a “correction” then a “dynamic mean off-set”. Anyone intested in the farce behind its derivation and the various attempts to prop it up, is invited to read my papers :

http://qualitydigest.com/IQedit/QDarticle_text.lasso?articleid=12564
http://qualitydigest.com/IQedit/QDarticle_text.lasso?articleid=12541

The extent of Six Sigma’s flaws are too numerous to describe here. My papers give greater detail.

Tom goes on to naively ask ‘what is the alternative?’ … has Deming been forgotten so soon ?

Yes, one should have a stable process to use a cpk as a prediction. But you and I both know that few of the users of cpk index values check process stability or report on it. Without that information, the number is meaningless.

But that is not what I was really getting at. Inherent in the very calculation of Six Sigma is a (mistaken) conversion of defect rate to a process capability model. Not only is this bad practice statistically, in the Six Sigma literature that I’ve seen (admittedly I haven’t read it all) there is no reference to the problem of citing a defect rate from a non stable source…no distinction is made when calculating that defect rate. Then that rate is used to form (mistakenly) a process capability to a given process.

The same is true with regard to the definition of area of opportunity and defect. With regard to defect, an operational definition is required. There is no other way to achieve a communicable meaning to a term like round, safe, clean, in-spec, etc. The same requirement exists for designating, in a communicable way, an area of opportunity for a defect to occur.

The most popular Six Sigma website (http://www.isixsigma.com/) barely mentions this vital need and the definition they give of operational definition is not correct. Another site (http://www.6sigma.us/) when searched returns no finding for operational definition. A third site, Motorola’s, does not have operational definition in its “Six Sigma Dictionary”.

Sigma is given as calculated using the total sample sum of squares. This is not correct unless the process is free of special causes and without a control chart one has no knowledge about the presence or absence of special causes.

Hypothesis testing is advocated (e. g. t Test for independent samples). First there is no reference that I could find that such a test has no meaning for prediction unless the samples are from a process in control. Moreover the pitfalls associated with hypothesis testing (type I and type II error for example) are virtually never explained.

It seems to me that the non-technical portion of your remarks falls into two categories. First you say that the “…improvement effort forces…” and later “…Six Sigma forces organizations…” I disagree. What forces the organization to do things is management. Many companies that do not ascribe to Six Sigma pay close attention to process stability, consistency of definitions, etc.

Second, you argue that there are no alternatives to some of the bad practices of Six Sigma. I disagree with that as well. There are very good alternatives. Toyota and Canon do not use a ‘Six Sigma” approach to quality or competitiveness and each company has been consistently been among the very best at quality for the products they produce and they have both been consistently very profitable in the same world markets that the U. S. has written off.

It has been said that, “The proof of the pudding is in the eating.” Using that homely advice we can look at Motorola and GE as Six Sigma exemplars and Toyota and Honda as non-users of Six Sigma and see that there is no comparison. General Electric is trying to sell its small appliance division. What a sad piece of news that is.

Thanks for your comment. I’ll respond shortly. Please stay tuned for Part II. Some of the valid issues you raise will be addressed.