What is Six Sigma? - Definition & Overview

Instructor: Deborah Schell

Deborah teaches college Accounting and has a master's degree in Educational Technology.

Companies want to manufacture a quality product to ensure customers will continue to purchase it and to allow the company to make a profit. In this lesson, you'll learn how Six Sigma drives quality.

An Overview of Six Sigma

Six Sigma is a statistical approach to improving business processes by reducing defects and their causes in the manufacturing process. The focus of Six Sigma is on reducing variation that occurs in the manufacturing process to improve product quality and increase company profit. Six Sigma initiatives take place in teams where members have expertise in a number of different areas, including financial analysis, project management and statistics.

Let's meet Mr. Rayne, who owns the Up and Away Umbrella company. The company is known for its high-quality products, but Mr. Rayne wonders if there's a way to reduce the number of defects that have arisen over the past six months. After a meeting with some of his managers, he agrees to implement a Six Sigma approach to reducing the defects.

Different Methodologies

There are two distinct methodologies in Six Sigma: DMAIC and DMADV. Both methods can be used to reduce defects in the manufacturing process, and both approaches use data to develop solutions to problems identified in the review process. There are differences in when each method should be used, which we'll examine in more detail below.


The DMAIC methodology is used in situations where a product is already being manufactured but is encountering defects and/or is not meeting customer expectations. The steps in this process are:

  • Define
  • Measure
  • Analyze
  • Improve
  • Control

In the define stage, goals of the project are developed, taking the customer's point of view into consideration. The measure stage involves identifying key parts of the process and gathering data about it. Once data is collected, it can be analyzed to determine the cause of the defects. The Six Sigma team can then brainstorm ways in which the current process can be improved to eliminate the identified defects. Lastly, steps can be taken to ensure future processing in this area continues to be defect-free.

Let's return to Mr. Rayne. Assume that a percentage of the company's high-wind umbrellas, which are meant to withstand winds up to 55 miles per hour, are failing. Consumers are unhappy with this product when it goes inside-out in high winds. Mr. Rayne has assembled a Six Sigma team of employees who are familiar with the methodology and represent different areas of the company. Let's examine how the Six Sigma team could use DMAIC to address this defect.

In the define stage, Mr. Rayne's team sets a goal of reducing the number of umbrellas that fail to one in 4 million manufactured umbrellas. Given the annual sales volume, this would represent a small number of defects that would impact very few customers.

In the measure stage, Mr. Rayne's team gathers data to identify under what conditions the umbrellas are failing and whether the failure can be isolated to a particular factory or period of time. The data reveals that the failures were occurring in umbrellas produced in its main plant between January and March.

As part of the analyze stage, the team investigates and determines that the failures are due to a change that was recently made in the manufacturing process. The thickness of the steel used in the umbrellas was reduced by 1/32 of an inch, as tests suggested that this change would not impact the structural integrity of the umbrellas. After discussion, the team concludes that the company needs to return to the original manufacturing specifications, even though it requires a little more steel to manufacture each umbrella.

To ensure a similar problem doesn't occur again, the team concludes that future manufacturing changes need to be controlled differently. They recommend that additional testing be built into the change process and that the testing involve a review of results by multiple areas to ensure that all parties are aware of the changes prior to final approval and implementation.


The DMADV methodology is appropriate when a product or process is being developed (i.e. it isn't currently in production or the process has already been changed through a DMAIC or some other review), but still isn't meeting Six Sigma goals or customer expectations. The steps in this process are:

  • Define
  • Measure
  • Analyze
  • Design
  • Verify

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