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What is Six Sigma?


Quality Glossary Definition: Six Sigma

Six Sigma is a method that provides organizations tools to improve the capability of their business processes. This increase in performance and decrease in process variation helps lead to defect reduction and improvement in profits, employee morale, and quality of products or services.

"Six Sigma quality" is a term generally used to indicate a process is well controlled (within process limits ±3s from the center line in a control chart, and requirements/tolerance limits ±6s from the center line).


Different definitions have been proposed for Six Sigma, but they all share some common threads:

  • The use of teams that are assigned well-defined projects that have a direct impact on the organization's bottom line.
  • Training in "statistical thinking" at all levels and providing key people with extensive training in advanced statistics and project management. These key people are designated “Black Belts.” Review the different Six Sigma belts, levels and roles.
  • Emphasis on the DMAIC approach to problem solving: define, measure, analyze, improve, and control.
  • A management environment that supports these initiatives as a business strategy.

Differing opinions on the definition of Six Sigma

Philosophy: The philosophical perspective of Six Sigma views all work as processes that can be defined, measured, analyzed, improved, and controlled. Processes require inputs (x) and produce outputs (y). If you control the inputs, you will control the outputs. This is generally expressed as y = f(x).

Set of tools: The Six Sigma expert uses qualitative and quantitative techniques or tools to drive process improvement. Such tools include statistical process control (SPC), control charts, failure mode and effects analysis, and process mapping. Six Sigma professionals do not totally agree as to exactly which tools constitute the set.

Methodology: This view of Six Sigma recognizes the underlying and rigorous approach known as DMAIC (define, measure, analyze, improve and control). DMAIC defines the steps a Six Sigma practitioner is expected to follow, starting with identifying the problem and ending with the implementation of long-lasting solutions. While DMAIC is not the only Six Sigma methodology in use, it is certainly the most widely adopted and recognized.

Metrics: In simple terms, Six Sigma quality performance means 3.4 defects per million opportunities (accounting for a 1.5-sigma shift in the mean).

What is lean Six Sigma?

The distinction between Six Sigma and lean has blurred. The term “lean Six Sigma” is being used more and more often because process improvement requires aspects of both approaches to attain positive results.

Six Sigma focuses on reducing process variation and enhancing process control, whereas lean drives out waste (non-value added processes and procedures) and promotes work standardization and flow. Six Sigma practitioners should be well versed in both.

Lean Six Sigma is a fact-based, data-driven philosophy of improvement that values defect prevention over defect detection. It drives customer satisfaction and bottom-line results by reducing variation, waste, and cycle time, while promoting the use of work standardization and flow, thereby creating a competitive advantage. It applies anywhere variation and waste exist, and every employee should be involved.


Integrating lean and Six Sigma

Lean and Six Sigma both provide customers with the best possible quality, cost, delivery, and a newer attribute, nimbleness. There is a great deal of overlap between the two disciplines; however, they both approach their common purpose from slightly different angles:

• Lean focuses on waste reduction, whereas Six Sigma emphasizes variation reduction.

• Lean achieves its goals by using less technical tools such as kaizen, workplace organization, and visual controls, whereas Six Sigma tends to use statistical data analysis, design of experiments, and hypothesis tests.

Often successful implementations begin with the lean approach, making the workplace as efficient and effective as possible, reducing waste, and using value stream maps to improve understanding and throughput. If process problems remain, more technical Six Sigma statistical tools may then be applied.

Learn more about combining lean and Six Sigma

Lean and Six Sigma - A One-Two Punch article

Lean and Six Sigma—A One-Two Punch

Using the Six Sigma/kaizen team-based approach, results are implemented faster with the participation of employees from the shop floor to the executive suite.
Better Together article Better Together
A simple group demonstration allows participants to gain an understanding of the advantages offered by lean and Six Sigma when they work together
  Lean-Six Sigma: Tools for Rapid Cycle Cost Reduction
Financial leaders should take leadership roles in deploying Lean-Six Sigma to improve costs for healthcare organizations: start today by taking a “Manager Quality Waste Walk.”

Implementing Six Sigma

Six Sigma implementation strategies can vary significantly between organizations, depending on their distinct culture and strategic business goals. After deciding to implement Six Sigma, an organization has two basic options:

  • Implement a Six Sigma program or initiative
  • Create a Six Sigma infrastructure

Option 1: Implement a Six Sigma Program or Initiative

With this approach, certain employees (practitioners) are taught the statistical tools from time to time and asked to apply a tool on the job when needed. The practitioners might then consult a statistician if they need help. Successes within an organization might occur; however, these successes do not build upon each other to encourage additional and better use of the tools and overall methodology.

When organizations implement Six Sigma as a program or initiative, it often appears that they only have added, in an unstructured fashion, a few new tools to their toolbox through training classes. One extension of this approach is to apply the tools as needed to assigned projects. It’s important to note, however, that the selection, management, and execution of projects are not typically an integral part of the organization.

Implementing a Six Sigma program or initiative can present unique challenges. Because these projects are often created at a low level within the organization, they may not have buy-in from upper management, which may lead to resistance from other groups affected by the initiative. In addition, there typically is no one assigned to champion projects across organizational boundaries and facilitate change.

A Six Sigma program or initiative does not usually create an infrastructure that leads to bottom-line benefits through projects tied to the strategic goals of the organization. Therefore, it may not capture the buy-in necessary to reap a large return on the investment in training.

For true success, executive-level support and management buy-in is necessary. This can help lead to the application of statistical tools and other Six Sigma methodologies across organizational boundaries.

Option 2: Create a Six Sigma Infrastructure

Instead of focusing on the individual tools, it is best when Six Sigma training provides a process-oriented approach that teaches practitioners a methodology to select the right tool, at the right time, for a predefined project. Six Sigma training for practitioners (Black Belts) using this approach typically consists of four weeks of instruction over four months, where students work on their projects during the three weeks between sessions.

Deploying Six Sigma as a business strategy through projects instead of tools is the more effective way to benefit from the time and money invested in Six Sigma training.

Consider the following Six Sigma deployment benefits via projects that have executive management support:

  • Offers bigger impact through projects tied to bottom-line results
  • Utilizes the tools in a more focused and productive way
  • Provides a process/strategy for project management that can be studied and improved
  • Increases communications between management and practitioners via project presentations
  • Facilitates the detailed understanding of critical business processes
  • Gives employees and management views of how statistical tools can be of significant value to organizations
  • Allows Black Belts to receive feedback on their project approach during training
  • Deploys Six Sigma with a closed-loop approach, creating time for auditing and incorporating lessons learned into an overall business strategy

A project-based approach relies heavily on a sound project selection process. Projects should be selected that meet the goals of an organization’s business strategy. Six Sigma can then be utilized as a road map to effectively meet those goals.

Initially, companies might have projects that are too large or perhaps are not chosen because of their strategic impact to the bottom line. Frustration with the first set of projects can be vital experience that motivates improvement in the second phase.

Six Sigma is a long-term commitment. Treating deployment as a process allows objective analysis of all aspects of the process, including project selection and scoping. Utilizing lessons learned and incorporating them into subsequent waves of an implementation plan creates a closed feedback loop and real dramatic bottom-line benefits if the organization invests the time and executive energy necessary to implement Six Sigma as a business strategy!


Six Sigma Case Studies

Six Sigma projects can bring benefits including increased organizational efficiency, improved customer satisfaction, reduced costs, increased revenues, and more. The Certified Six Sigma Black Belt Handbook reports that many Six Sigma Black Belts “manage four projects per year for a total of $500,000–$5,000,000 in contributions to the company’s bottom line.” A 2012 study of 28 organizations showed that “effective implementation of Six Sigma led to … an average return of more than $2 in direct savings for every dollar invested.”

The following case studies provide a closer look at results organizations have achieved using Six Sigma. Visit ASQ's Quality Resources to read more. Does your organization have Six Sigma results to share? Let ASQ publish your success story.

Supply Chain Techniques Applied to Six Sigma Saves SeaDek Marine Products $250,000

Supply Chain Techniques Applied to Six Sigma Saves SeaDek Marine Products $250,000 – August 2016
SeaDek used supply chain techniques and Six Sigma to reduce major inventory stockouts in 2015. Inventory control tools were applied using DMAIC methodology. The company went from 14 major stockouts in 2014 to one stockout in 2015, resulting in a materials cost savings of more than $250,000 and improving on-time delivery from 44 percent the previous year to 95 percent in 2015.

YMCA Upgrades Day Camps Using Six Sigma

YMCA Upgrades Day Camps Using Six Sigma – January 2016
When a senior leader at the YMCA of the USA introduced Six Sigma to the youth development department, a new method for managing and tracking projects was ushered into the organization. Upon completing a Green Belt-level training course, a YMCA project team used Six Sigma tools to improve the culture of the organization’s summer day camp. As staff became more comfortable using Six Sigma, project work became more organized and data-driven, and the project team exceeded its first-year goals. 

QP April 2015 cover for KC

Achieving Customer Specifications through Process Improvement Using Six Sigma (PDF) – April 2015
The NutriSoil Company in Portugal, a small and medium-sized enterprise (SME), sells fertilizer in bags. The company has had problems with its filling process due to excess weight of the bags. Results show that by implementing Six Sigma combined with the 5S program, NutriSoil achieved an improvement in its Cpk index for this process, which increased consumer satisfaction and a highly significant cost savings. This resulted in increased competitiveness.

Driving Business Impact for Key Customers article

Driving Business Impact for Key Customers (PDF) – February 2015
This article discusses how lean and Six Sigma approaches were used for process improvement by CMITS, a business group within Genpact, a business consulting firm. CMITS focuses on information technology (IT) and IT-managed projects. All of 2012 was spent building lean and Six Sigma within CMITS and introducing Six Sigma tools for process improvement.

Let It Flow case study

Let It Flow (PDF) – February 2015
Thomas Jefferson University Hospitals in Philadelphia has a large volume of inpatient and outpatient surgical volume flowing through its many operating rooms. The operating room is a setting abundant with opportunities for improvement. System inefficiencies can lead to sub-optimization of operating room use, thereby decreasing revenue generation. In 2010, the department underwent a strategic plan overview to identify opportunities to streamline and improve operational processes.

Mega Pack case study

Mega Pack Line Blow-Up: DMAIC Roadmap Leads Boston Scientific Heredia to Reengineer Packaging Lines – December 2014
Corporate rates of improvement at Boston Scientific represent a yearly challenge and opportunity to improve and exceed different operation indicators such as service and efficiency, safety, quality, and cost within the company. A DMAIC roadmap provides a standardized and recognized set of tools to be used as methodology during part of the project implementation, based on a lean manufacturing point of view. Core team members and product builders within the Amplatz Super Stiff™ Guidewires area worked together to improve efficiency, increase safety, and save money using a DMAIC roadmap.

Quality Progress magazine cover

Rock Solid: Combining lean, Six Sigma and theory of constraints creates a process improvement powerhouse – December 2014
The 6TOC improvement method employs elements of Six Sigma, lean and the theory of constraints (TOC) to zero in on process bottlenecks and eliminate waste and variation. A 10-step implementation plan based on Eliyahu Goldratt’s chain project management process and Joseph M. Juran’s management principles can help any industry implement 6TOC.

Nigerian Banking Industry case study

Six Sigma Optimization of Mystery Shopping – September 2014
Mystery shopping (MS) can be a very valuable exercise for studying and evaluating service delivery performance within the banking industry. Using Six Sigma tools and hypothetical data, this case study tests the approach and results to gauge poor service from excellent service delivery. The MS approach is highly applicable as a balanced scorecard parameter to measure delivery within service centers.

Six Sigma Quotes

These popular quotes related to Six Sigma come from ASQ's Quality Quotes collection. 

“Measurement is the first step that leads to control and eventually to improvement. If you can’t measure something, you can’t understand it. If you can’t understand it, you can’t control it. If you can’t control it, you can’t improve it.”
- H. James Harrington

“Quality cannot be copied; there is no step-by-step cookbook that applies equally to all company situations and cultures.”  
- Ernst & Young

“I believe the leader’s ultimate job is to spread hope. “
- Bob Galvin (Motorola)

“The World-Class organization is continuously bathed in a stream of integrated data.”
- Y.S. Chang, George Labovitz, and Victor Rosansky

“Quality depends on good data. It also depends on executive leadership in using that data.”
- Juran Institute, Inc.

“Observing many companies in action, I am unable to point to a single instance in which stunning results were gotten without the active and personal leadership of the upper managers. “
- Joseph M. Juran

“The transformation to world-class quality is not possible without committed, visionary, hands-on leadership.”
- Steven George

Help build the collection. Submit your own quote on Six Sigma.

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