The basics behind the Six Sigma quality control technique
Six Sigma is designed to achieve excellence in customer service and measure deviation from the ideal. It provides a process for placing value on the intangible nature of quality control. The underlying theories of Six Sigma are highly technical and complex. This book is a basic guide to those who are new to the concept, and though this is a complex subject, the concepts involved are not too complex for readers to grasp. Getting Started in Six Sigma demonstrates how an employee or supervisor can implement Six Sigma successfully without having to become technically familiar with process-oriented models or statistical modeling.
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Yes, you can access Getting Started in Six Sigma by Michael C. Thomsett in PDF and/or ePUB format, as well as other popular books in Business & Business General. We have over one million books available in our catalogue for you to explore.
Many years ago at Fishermanâs Wharf in San Francisco, I saw a fisherman sewing up holes in his net. The net was quite large and he had lain it out over a wide expanse of the dock. I watched him for quite some time, noticing that he paid careful attention to even the smallest tear, methodically repairing each one in turn. When he took a break I walked over to him. âWhy do you have to fix all the tears, even the little ones?â I asked him. He explained, âIt only takes one small tear for all of the fish to escape.â
Perfectionâimpossible to achieve completely and all of the timeâis a goal worth keeping in mind. If we set our sights any lower, we deserve what we get. If we settle for 80 percent or 70 percent, we can never expect to reach 95 percent or 98 percent. As the old fisherman explained, even the smallest imperfection affects the entire effort. A small tear in the net becomes a bigger tear and the fish escape as the net is pulled in. The corporate world works in the same way. What might seem a minor imperfection or a flaw in a remote department affects you and your product or service. The solution: We have to find all the tears and repair them, methodically and completely. Yes, new tears will appear in the net, but we cannot shrug and explain, âWe found most of them.â We also cannot just shrug and say, âItâs not my job.â Perfection is not a requirement, but it is a goal worth setting. We can then compare our outcomes to the goal, seeing improvement and measuring it against that goal.
THE ORIGINS OF SIX SIGMA
Sigma is the letter in the Greek alphabet used to denote standard deviation, a statistical measurement of variation, the exceptions to expected outcomes. Standard deviation can be thought of as a comparison between expected results or outcomes in a group of operations, versus those that fail.
sigma
the level of variation compared to an average; the Greek letter, Ď used by statisticians to denote standard deviation.
standard deviation
the degree of exception, or variation from the average, in a group of outcomes, used to describe exceptions to an expected result.
The measurement of standard deviation shows us that rates of defects, or exceptions, are measurable. Six Sigma is the definition of outcomes as close as possible to perfection. With six standard deviations, we arrive at 3.4 defects per million opportunities, or 99.9997 percent. This would mean that at Six Sigma, an airline would lose only three pieces of luggage for every one million that it handles; or that the phone company would have only three unhappy customers out of every one million who use the phone that day. The purpose in evaluating defects is not to eliminate them entirely, but to strive for improvement to the highest possible level that we can achieve.
Six Sigma
a measurement denoting near perfection, representing six standard deviations or 3.4 million defects per million operations; the ideal against which actual performance is measured.
Key Point We evaluate defects to improve overall performance, knowing that eliminating them completely is unrealistic.
We know that trying to achieve Six Sigma would be impractical on a consistent basis; so while it is a desirable goal, it presents a model against which we can measure our performance. So rather than setting the unrealistic goal of achieving perfection, we can observe (1) our current Sigma level and (2) improvement in that level as changes are made.
Table 1.1 presents an abbreviated summary of Sigma level, defects per million, and yield, or success rate of the outcomes.
You can identify your level of Sigma performance and then compare it to the chart. This is where the benefits of Six Sigma are realized. By comparing your outcomes to the ideal outcome of Six Sigma, you can quantify quality itself.
TABLE 1.1 Sigma Table
Sigma
Defects per Million
Yield
6.0
3.4
99.9997%
5.0
233.0
99.977
4.0
6,210.0
99.379
3.0
66,807.0
93.32
2.5
158,655.0
84.1
2.0
308,538.0
69.1
1.5
500,000.0
50.0
1.4
539,828.0
46.0
1.3
579,260.0
42.1
1.2
617,911.0
38.2
1.1
655,422.0
34.5
1.0
691,462.0
30.9
0.5
841,345.0
15.9
0.0
933,193.0
6.7
Example: Your department performed 535 specific operations last month. Of these, 43 were defective (they fell outside the acceptable range of outcomes). This means that 492 of the operations were successful. The yield was:
Referring to Table 1.1, we discover that this outcome represents Sigma somewhere between 2.5 and 3. If you were able to reduce the number of defects by half, ending up with 21, your acceptable outcomes would then grow to 514 out of 535 operations, and your yield would increase as well:
Now the Sigma is between 3 and 4, a significant improvement. Of course, if you cut defects in half, you are going to know your outcomes have improved, so what purpose does Six Sigma provide beyond the obvious scorekeeping? As the preceding example demonstrates, improvement in quality can be specifically measured. In practice, you may be dealing with a much greater volume of outcomes, and the incremental rate of success is likely to be smaller than that shown in the example; and Six Sigma is far more than a measuring system. It is a way of doing things, a change in cultural attitude that is designed to create a company-wide team in practical terms. As far as the scorekeeping aspects of Six Sigma go, if you begin with an assumption that a change in procedures will produce an expected change in outcomes, you can then compare actual to projected results to judge the success of your work.
Key Point What makes Six Sigma different from most other quality control programs? It is more than just a way to improve performance; it is a method for changing the corporate culture, from top to bottom.
An âoperationâ can be any function you performâdelivery of goods, telephone contact, balancing accounts, or executing a repair, for example. Any operation is measurable in Sigma terms. The desired outcome represents satisfaction of the customerâs expectation, and any time that expectation is not met, the outcome is defective.
While measuring results is a crucial part of the process, you will be more concerned with how Six Sigma is applied and what role you and other employees will perform within that process. So the idea of Six Sigma is much more than the latest approach to quality control; it represents a change in philosophy that affects everyone. It is designed to bring everyone into a single team with the same overall goals. So many corporate employeesâespecially in large organizationsâhave a sense of isolation or view their relatively small department as a realm unto itself. Six Sigma encompasses the enti...
Table of contents
Cover
Table of Contents
Introduction: Striving for Perfection in an Imperfect World
