sixsigma

Six Sigma (often written as six sigma) is a data-driven approach and management philosophy for improving the quality of process outputs by identifying and removing the causes of defects and minimizing variability in processes. It originated at Motorola in the mid-1980s and was popularized in the United States by General Electric in the 1990s, becoming a widely adopted framework in manufacturing and services.

The core methodology is composed of two project-driven sequences: DMAIC for improving existing processes and DMADV for developing new processes or products. Define the problem and goals, Measure key aspects, Analyze data to identify root causes, Improve by implementing solutions, and Control the process to sustain gains. DMADV stands for Define, Measure, Analyze, Design, Verify.

A belt-based organizational structure assigns roles such as White/Yellow/Green/Black Belts, each with training and project responsibilities. Projects are typically chartered with goals, scope, and metrics, including the target defect rate or DPMO (defects per million opportunities) and the sigma level.

Common tools include statistical methods, control charts, Pareto analysis, cause-and-effect diagrams (Ishikawa), failure modes and effects analysis (FMEA), design of experiments (DOE), and SIPOC diagrams. Six Sigma often overlaps with Lean, forming Lean Six Sigma to emphasize both speed and quality.

Applications span manufacturing, services, IT, healthcare, and supply chains. Criticisms include potential overemphasis on metrics, implementation complexity, and reliance on data availability; success hinges on organizational support, clear problem selection, and sustained leadership commitment.