What is 6 Sigma? Defect rate 3.4 Quality management viewed from DPMO goals and DMAIC

What if out of a million products made in a factory, only a few are defective? Six Sigma is a management method that solves problems using statistics and data with the goal of achieving this level of quality. Let's summarize the meaning and procedures of 6 Sigma and how it is used in production management.

What does 6 Sigma mean?

Sigma is a symbol that means standard deviation in statistics. The meaning of the name Six Sigma is to reduce the dispersion to the extent that there are six standard deviations between the process average and the standard limit.

In practice, the process average is believed to fluctuate by about 1.5 sigma over the long term, and the Six Sigma level is explained as 3.4 defects per million opportunities, or 3.4 DPMO. The key is the idea of ​​measuring and managing quality with data rather than the numbers themselves.

How did it start and spread?

Six Sigma began around 1986 when Bill Smith, an engineer at Motorola, organized it as a quality improvement method. Through this, Motorola was recognized for its quality innovation achievements.

In the mid-1990s, GE's Jack Welch introduced Six Sigma throughout the company and became world famous. In Korea, the introduction has continued since the late 1990s, mainly in large manufacturing companies such as electronics and chemicals.

발표 연습은 소리 내서 두 번만 해도 실제로 말이 훨씬 매끄러워지더라고요. 연습할 때 휴대폰으로 녹음해서 들어 보는 것도 좋을 것 같아요.

What kind of procedure is DMAIC?

DMAIC is an acronym for Define, Measure, Analyze, Improve, and Control. This is the order of defining a problem that is important to the customer, measuring the current level, analyzing the cause, and then implementing and maintaining the solution.

When designing a new product or process from scratch, a transformation procedure such as DMADV is sometimes used. Either way, the principle of judging with data, not intuition, is the same.

What is the relationship between the belt system and TQM?

6 Sigma divides personnel into green belts, black belts, and master black belts according to expertise, like a belt in martial arts, and has them lead the project. Six Sigma and Comparing total quality management (TQM), the difference is that while TQM emphasizes a company-wide quality culture, Six Sigma operates on a project-by-project basis with clear financial performance.

The two methods complement each other rather than opposing each other. The effectiveness increases when 6 Sigma's statistical tools and project management are added to the TQM culture that views quality as the responsibility of all members.

How can we improve production management?

At the manufacturing site, the first step is to collect data from the process where defects occur most often and narrow down the cause. Lean Six Sigma, combined with lean production to reduce waste, is widely used as a method to improve both speed and quality.

However, formal operations that only increase the number of projects and belt certifications actually increase fatigue in the field. Only with consistent support from management and participation from field workers can Six Sigma lead to actual results.

When studying Six Sigma, try directly applying DMAIC to a small problem in your daily life. If you practice with problems that can be easily counted, such as the number of times you are late in the morning, you will understand why the five steps are in that order.

This article was compiled by the Campus Down editorial department after checking major textbooks and open literature · Review 2026-10-26. References: Pyzdek, T. & Keller, P., The Six Sigma Handbook; Harry, M. & Schroeder, R., Six Sigma (2000); Motorola Solutions, Six Sigma history; American Society for Quality (ASQ), Six Sigma Belts, Executives and Champions. This is an introductory level summary, so we recommend that you read the original text directly for an in-depth discussion.