|Critical to Quality||Customer Performance requirements|
|Characteristics (CTQ)||of a Product or Service|
|Defect||Any Event that does not meet the specifications of a CTQ|
|Defect Opportunity||Any Event which can be measured that provides a Chance of not meeting a Customer CTQ|
The term sigma is used to designate the distribution or spread about the mean (average) of any process or procedure.
For a business or manufacturing process, the sigma capability (z-value) is a metric that indicates how well that process is performing. The higher the sigma capability, the better. Sigma capability measures the capability of the process to perform defect-free work. A defect is anything that results in customer dissatisfaction.
|Process Capability||Defects per million Opportunities|
The Science: We don't know what we don't know.
The Art: If we can't measure it, we really don't know much about it. If we don't know much about it, we can't control it.
The Magic: If we can't control it we are at the mercy of chance
The statistical objectives of Six Sigma can be best understood from the diagram below:
The table below enumerates the improvement possibilities after six sigma implementation.
|The classical view of Quality|
99% Good (3.8σ)
|The Six Sigma view of Quality|
99.9996% Good (6σ)
|30,000 ton of defective steel production in a steel plant every year.||1200 ton of defective steel production in the steel plant per year|
|87 hours of Power supply failure in a machine shop per year||3 hours of Power supply failure in the machine shop per year|
|20,000 lost articles of mail per hour||Seven lost articles of mail per hour|
|Unsafe drinking water almost 15 minutes each day||One minute of unsafe drinking water every seven months|
|5,000 incorrect surgical operations per week||1.7 incorrect surgical operations per week|
|2 short or long landings at most major airports daily||One short or long landing at most major airports every five years|
|200,000 wrong drug prescriptions each year||68 wrong drug prescriptions each year|
The key features of six sigma and the process improvement possibility after implementation, vis.-à-vis. classical approach to quality improvement, is that six sigma focuses on:
To efficiently drive improvements, the focus must be on the inputs (Xs) to the process. The word sigma is used in two ways, to describe capability and to describe variation. As DPMO goes down, process capability goes up.
Rajeev Kumar is the primary author of How2Lab. He is a B.Tech. from IIT Kanpur with several years of experience in IT education and Software development. He has taught a wide spectrum of people including fresh young talents, students of premier engineering colleges & management institutes, and IT professionals.
Rajeev has founded Computer Solutions & Web Services Worldwide. He has hands-on experience of building variety of websites and business applications, that include - SaaS based erp & e-commerce systems, and cloud deployed operations management software for health-care, manufacturing and other industries.