Measuring Quality Quantitatively
DMAIC: define, measure, analyze, improve, control
DMADV: define, measure, analyze, design, verify
What is Six Sigma?
You may find an excellent, constantly updated website: http://www.isixsigma.com where is the following Six Sigma explanation:
Six Sigma at many organizations simply means a measure of quality that strives for near perfection. Six Sigma is a disciplined, data-driven approach and methodology for eliminating defects (driving towards six sigma between lower and upper specification limits) in any process — from manufacturing to transactional and from product to service.
The statistical representation of Six Sigma describes quantitatively how a process is performing. To achieve Six Sigma, a process must not produce more than 3.4 defects per million opportunities. A Six Sigma defect is defined as anything outside of customer specifications. A Six Sigma opportunity is then the total quantity of chances for a defect. Process sigma can easily be calculated using a Six Sigma calculator.
The fundamental objective of the Six Sigma methodology is the implementation of a measurement-based strategy that focuses on process improvement and variation reduction through the application of Six Sigma improvement projects. This is accomplished through the use of two Six Sigma sub-methodologies: DMAIC and DMADV. The Six Sigma DMAIC process (define, measure, analyze, improve, control) is an improvement system for existing processes falling below specification and looking for incremental improvement. The Six Sigma DMADV process (define, measure, analyze, design, verify) is an improvement system used to develop new processes or products at Six Sigma quality levels. It can also be employed if a current process requires more than just incremental improvement. Both Six Sigma processes are executed by Six Sigma Green Belts and Six Sigma Black Belts, and are overseen by Six Sigma Master Black Belts.
According to the Six Sigma Academy, Black Belts save companies approximately $230,000 per project and can complete four to 6 projects per year. General Electric, one of the most successful companies implementing Six Sigma, has estimated benefits on the order of $10 billion during the first five years of implementation. GE first began Six Sigma in 1995.
Many frameworks exist for implementing the Six Sigma methodology. Six Sigma Consultants all over the world have developed proprietary methodologies for implementing Six Sigma quality, based on the similar change management philosophies and applications of tools.
I (Horst Grothus) am not a Six Sigma Consultant, even though “my” Zero Defects Management methodology follows some of the principles mentioned above.
Additional essentials of my policy are these:
- I don’t presume Chronic defects to dominate (but rather sporadic incidents)
- I expect nearly all defects to be triggered by several simultaneous chain reactions
- This is why I am less interested in the individual Active Faults and errors that have triggered an individual defect. If I could avoid these faults, I would just prevent the same defect to occur again. However, Sporadic Defects don’t repeat anyway (by definition). I apply the thorough analysis of a statistically representative sample of defects rather in order to find the permanent failures provoking defects of other kinds at other spots.
- I consider Basic Risk Factors (permanent and everywhere lurking Management failures) to be the real Root Causes (that thus have to be eliminated)
- You will find at least one human error in literally every reaction chain leading to a defect. I consider it to be impossible to define each potential human error. Therefore, I am unable to predict the kind and number of errors, to quantify the Sigma value and to economically and efficiently design actions, avoiding all these errors.
- I therefore do not rely only on “pro-active” actions (directly aiming at the immediate error or failure triggering the Quality Defects occurring); but rather I first collect a statistically representative number of defect analyses and identify the Risk Profile of their Basic Risk Factors
- The same is true for Chronic (same properties repeating) defects:, because Management failures seems to tolerate them to repeat