Six Sigma - Short Note

Six Sigma is a disciplined, data-driven quality/process improvement methodology developed by Motorola (1986) and popularised by GE. The Greek letter sigma (σ) denotes standard deviation; Six Sigma means only 3.4 defects per million opportunities (DPMO), i.e. 99.99966% defect-free output.

Core Idea

• Identify defects and variation in a process, then remove their root causes so that the process output is consistently within customer specifications.
• Focus is on improving the process, not blaming the people.

Two Project Methodologies

DMAIC (improve existing process)	DMADV / Design for Six Sigma (create new process)
Define - problem, goals, team	Define - customer needs and goals
Measure - current performance	Measure - CTQs (critical to quality) characteristics
Analyze - find root causes	Analyze - design alternatives
Improve - implement and verify solution	Design - detailed design
Control - sustain the gains	Verify - validate the design with trials

Quality Levels (Sigma Levels)

Sigma Level	DPMO	Yield
4σ	6,210	99.38%
5σ	233	99.9767%
6σ	3.4	99.99966%

Roles (Belt System)

• Champion - sponsors the project
• Master Black Belt - trains and mentors
• Black Belt - leads projects full time
• Green Belt - assists part time
• Yellow Belt - basic awareness

Advantages

• Fewer defects, lower cost of poor quality and rework.
• Higher customer satisfaction and consistency.
• Data-driven decisions, measurable results.
• Works for manufacturing and service/software processes.

Limitations

• Needs strong management commitment and trained experts.
• Over-emphasis on statistics can slow small projects.
• Success depends on cultural change, not just tools.

Conclusion: Six Sigma, usually combined with Total Quality Management (TQM), gives a systematic, measurable way to drive defects towards zero.