Introduction^[1]

Six Sigma is a highly disciplined process that helps organisations that adopt it to focus on developing and delivering near-perfect products and services. For those who haven’t heard it mentioned, I can confirm it is alive and well, although not grabbing the new as it did 15 or so years ago.^[2]

If, as I hope, you want to learn about Six Sigma, who ‘invented’ it and why, and its application both to manufacturing and the services sectors, with examples of how it is being applied, please read on.

Six Sigma is a data-driven quality improvement methodology originally developed by Motorola in the US in 1986^[3]. Its goal was to reduce defects and improve efficiency by using statistical methods to identify and eliminate the root causes of problems. Although the process is often applied to the manufacturing sector, it has also been applied in service industries such as finance, legal, banking and medical.

You might be thinking of several questions, such as: could Six Sigma be the answer to how public transport is run, or how the NHS and medical profession operates, how professional services are delivered, or even could HMRC operate a fairer and responsive tax system – the answer to all these questions is a resounding YES.

This goal of Six Sigma is based on the philosophy that the process (of making something or providing a service) must be stable and in control and that the rate of defects must be low enough to meet the customer’s expectations. The Six Sigma methodology uses statistical methods and data analysis to identify and eliminate the root causes of defects, with the ultimate goal of achieving near-perfect performance.

The Real Power of Six Sigma
“The real power of Six Sigma is simple, because it combines people power with process power.”
Source: Subir Chowdhury, The Power of Six Sigma

What does “Sigma” mean?
The word Sigma is a statistical term that measures how far a given process deviates from perfection. Thus, Six Sigma is a management philosophy focused on eliminating mistakes, waste and rework – the central notion behind it is that if you can measure how many “defects” you have in a process, you can systematically work out how to eliminate them and get as close to “zero defects” as possible. Zero defects mean quality and perfection. It cuts costs, increases customer satisfaction and contributes more than anything else to business success.

Statistical Reference
Sigma – the word is taken from the Greek alphabet – is a statistical reference for measuring variation in data:

• The Six Sigma methodology originated at Motorola in the 1980s as a means for comparing variation in any process related to customer satisfaction.
• A sigma level of six means that defects occur within a process only 3.4 times in one million chances (called ‘opportunities’).
• The level is determined using process yield, or Defects per Million Opportunities (DPMO). If you know your process yield, it’s easy to identify your sigma level right now by checking where you are on the sample sigma conversion table below.

Most businesses operate at a three- to four-sigma level, where the cost of defects is roughly 20% to 30% of income. By approaching Six Sigma (3.4 per 1 million opportunities), the cost of quality drops to less than 1% of sales. Although having zero defects is the goal, as a measure Six Sigma will drive a business toward achieving higher levels of customer satisfaction and reducing operational costs.

Six Sigma is a robust continuous improvement strategy and process that includes cultural methodologies such as Total Quality Management (TQM), process control strategies such as Statistical Process Control (SPC) and other important statistical tools. It uses a structured systems approach to problem-solving and strongly links initial improvement goal targets to bottom-line results.

Sigma (uppercase Σ, lowercase σ) is the 18^th letter of the Greek alphabet and has several meanings, including:

• A mathematical symbol that is used to represent the summation of a series of numbers or to describe standard deviation.
• In physics and engineering, it represents conductance, a measure of electrical conductivity.
• In statistics, it is used to describe the population standard deviation.
• In set theory, it is used to describe the set of all possible combinations of a given set.
• In finance, it is used to describe the sensitivity of an option’s price to changes in the underlying stock price.

Sigma is also used in many other fields, including:

• In biology, it describes the sum total of all the genetic information in an organism’s chromosomes.
• In linguistics, it is used to describe a speech sound that is intermediate between a voiced and voiceless sound, such as the “s” sound in “sin” and “zen”.
• In optics, it is used to describe the sigma value, a measure of the spot size of a laser beam.
• In geology, it is used to describe the sigma scale, a measure of rock strength.
• In Greek mythology, Sigma is sometimes associated with the god Zeus.

Focusing on the Key Element of Quality
There are three key elements of quality: customer, process and employee. If an organisation wants to be and remain a world-class quality company, it needs to focus on those three essential elements. Customers value consistent, predictable business processes that deliver world-class levels of quality: that is exactly what Six Sigma strives to produce.

What does an organisation need to do to become a Six Sigma company?

• Develop a clear understanding of Six Sigma principles and methodologies.
• Appoint a senior executive to lead the Six Sigma initiative.
• Train and certify employees as Six Sigma Green Belts, Black Belts, and Master Black Belts.
• Implement Six Sigma tools and methodologies in all departments and processes.
• Establish a system for tracking and measuring the success of Six Sigma projects.
• Incorporate Six Sigma into the organisation’s culture and strategic objectives.
• Continuously evaluate and improve the implementation of Six Sigma.

It is important to note that becoming a Six Sigma company is a significant investment in time, resources, and money, but it can bring many benefits, such as increased efficiency, reduced defects, and improved customer satisfaction. In fact, everybody wins.

Lean Six Sigma
Lean Six Sigma is a methodology that combines Lean, a process improvement approach, with Six Sigma, a quality improvement approach, to enhance the speed, efficiency and quality of processes in organisations. The main goal of Lean Six Sigma is to minimise waste, reduce defects and minimise variability in processes, leading to increased customer satisfaction, improved efficiency and increased profitability.

In practice, Lean Six Sigma combines Lean’s focus on eliminating waste and non-value-added activities with Six Sigma’s emphasis on data-driven problem-solving and defect reduction. This integration results in a comprehensive, end-to-end process improvement methodology that can be applied to many processes and industries, including manufacturing, healthcare, finance, and more.

Six Sigma Belts Explained

Black Belt:
Someone trained in the Six Sigma methodology and experienced leading cross-functional process improvement action teams. Acts as a full-time team leader responsible for measuring, analysing, improving and controlling key processes that influence customer satisfaction and/or productivity growth.

Green Belt:
An individual trained in the Six Sigma methodology. A team member of six sigma process improvement action teams. Similar to Black Belt but not a full-time position.

Yellow Belts:
Employees who continue to work in their current assignment but receive training in Six Sigma methods to allow them to contribute more to their organisation’s involvement in Six Sigma.

Master Black Belt:
Someone trained in the Six Sigma methodology who acts as the organisation wide Six Sigma programme manager. Oversees Black Belts and process improvement projects and provides guidance to Black Belts as required. A Master Blackbelt teaches other Six Sigma students and helps them achieve Greenbelt and Blackbelt status. First and foremost, they are teachers but they also review and mentor Black Belts. Selection criteria for Master Black Belts are quantitative skills and the ability to teach and mentor. Master Black Belts are full-time positions.

To implement Lean Six Sigma, organisations typically designate employees as Green Belts, Black Belts or Master Black Belts^[4], who are trained in Lean Six Sigma methodologies and tools and then lead process improvement projects within the organisation. The projects typically follow a defined process improvement roadmap, such as the DMAIC (Define, Measure, Analyze, Improve, Control) model used in Six Sigma, and involve data collection, analysis and implementation of improvement recommendations.

The Lean Six Sigma approach has been successfully implemented by many organisations, leading to significant cost savings, improved quality and customer satisfaction, and increased competitiveness.

Alternatives to Six Sigma
There are several approaches and methodologies that are considered to be alternatives or enhancements to Six Sigma. Some of the most commonly mentioned include:

• Agile: Agile is a project management and software development methodology that emphasises flexibility and responsiveness to changing requirements. It is an approach to project management that emphasises flexibility, collaboration, and iterative development. The approach was developed in the software development industry in the 1990s as a response to the limitations of traditional “waterfall” project management. Agile involves working in short sprints, focusing on delivering value to the customer, continuous feedback, and a focus on customer satisfaction as well as adapting to changing requirements. There are several different Agile frameworks, including Scrum, Kanban, Lean Startup, and Extreme Programming (XP). Agile is often used in place of or in combination with Six Sigma in organisations looking for a more flexible and adaptive approach.
• Business Process Reengineering (BPR): BPR is a methodology that focuses on fundamentally rethinking and redesigning business processes to achieve significant improvements in quality, efficiency, and customer satisfaction. It involves a comprehensive analysis of the entire process and requires substantial changes to an organisation’s structure and culture. The BPR approach was popularised in the 1990s by Michael Hammer and James Champy in their book Reengineering the Corporation. BPR involves questioning the fundamental assumptions and goals of a process and then rethinking and redesigning it from scratch using a cross-functional team and a customer-centric perspective.
• Customer Experience Management (CEM): CEM is a methodology that focuses on managing the customer experience by understanding and meeting customer needs and expectations. It involves various techniques, including customer research, journey mapping, and feedback analysis, to identify areas for improvement and enhance the overall customer experience. The methodology has roots in the service industry, where it has been used to improve customer satisfaction and loyalty. CEM involves techniques such as customer research, journey mapping, and feedback analysis. It can be applied to a diverse range of industries.
• Design for Six Sigma (DFSS): DFSS is a quality management methodology focused on designing products and processes optimised for quality. It is similar to Six Sigma in that it uses statistical analysis and data-driven decision-making, but it is applied earlier in the product development process. It was developed in the 1990s as an extension of Six Sigma, focusing on preventing defects through design rather than identifying and eliminating them after the fact. DFSS involves a structured approach to product and process design that includes tools such as QFD (Quality Function Deployment), TRIZ (Theory of Inventive Problem Solving), and Design of Experiments (DOE).
• Design Thinking: Design Thinking is a problem-solving methodology emphasising empathy, experimentation, and rapid prototyping. It is often used in place of or in combination with Six Sigma in organisations that are looking for a more creative and human-centred approach to problem-solving. It is regarded as a human-centred approach to problem-solving and innovation and was developed in the design industry in the 1990s. The approach involves understanding and empathising with users, defining the problem and generating ideas, prototyping and testing solutions, and then implementing and scaling the solution. Design Thinking provides a structured process for creativity and innovation that can be applied to various industries and problems.
• ISO 9000: ISO 9000 is a family of standards that provide a framework for quality management. The standards are focused on establishing a quality management system that is designed to meet customer requirements, improve customer satisfaction, and continually improve the effectiveness of the system. The standards were first published by the International Organization for Standardization (ISO) in 1987, and they have since been revised and updated several times.
• Kaizen: Kaizen is a Japanese term that means “continuous improvement.” The approach involves making small, incremental improvements to a process over time, focusing on involving everyone in an organisation in the pursuit of improvement. Kaizen is often used in conjunction with other quality management methodologies, such as TQM and Lean. It was popularised by Masaaki Imai in his book “Kaizen: The Key to Japan’s Competitive Success,” and companies across a range of industries have used it.
• Lean and Lean Manufacturing (also known as Lean Production) is based on the Toyota Production System, which includes principles such as “Just-in-Time” (JIT) production, “Jidoka” (automation with a human touch), and “Kaizen” (continuous improvement) as a system for reducing waste and improving efficiency in manufacturing. It is a continuous improvement methodology focusing on reducing waste and increasing efficiency in a value stream by identifying and eliminating non-value-added activities to improve flow and reduce lead times. It involves using techniques such as value stream mapping, continuous flow, and pull systems to eliminate non-value-added activities and improve production processes. Lean is often used in combination with Six Sigma, in a method known as Lean Six Sigma.
• Statistical Process Control (SPC): SPC is a methodology that uses statistical tools and techniques to monitor and control production processes using statistical methods. The goal of SPC is to identify and eliminate sources of variation in the production process, which can lead to defects and reduced quality. The approach was developed in the 1920s by Walter Shewhart, a quality management expert who worked for Bell Laboratories. SPC involves using control charts to monitor process performance, identify sources of variation, and take corrective action as needed.
• Theory of Constraints (TOC): TOC is a methodology that focuses on identifying and eliminating constraints that limit the overall performance of a system. The approach is based on the idea that every system has at least one constraint that limits its ability to achieve its goals, and by identifying and addressing that constraint, overall performance can be improved. It is a management philosophy developed by Eliyahu Goldratt^[5] in the 1980s. The approach involves identifying and removing bottlenecks in a process, with a focus on improving throughput and reducing lead times. TOC emphasises the importance of balancing flow, inventory, and capacity, and it provides tools such as the Five Focusing Steps and the Drum-Buffer-Rope scheduling methods.
• Total Quality Management (TQM): TQM is a comprehensive approach to quality management that emphasises continuous improvement and customer satisfaction. TQM is a holistic approach to quality management developed in the 1950s and 1960s by W. Edwards Deming, Joseph M. Juran, and other quality management experts. It emphasises a team-based approach to problem-solving and encourages everyone in an organisation to take responsibility for quality. It is often considered a precursor to Six Sigma, and many of its principles are incorporated into the Six Sigma methodology.

These are just a few examples of the many approaches and methodologies that are considered to be alternatives or enhancements to Six Sigma. The best strategy will depend on specific needs and goals, as well as the culture and capabilities of the organisation, which must evaluate options and select the right approach for them. While each quality management methodology has unique characteristics and is suited to different organisational contexts and goals, many of them can be applied across various industries, including manufacturing, finance, law, the medical field, and creativity.

Origins of Six Sigma
In the mid-1980s, the Chairman of Motorola calculated his company’s quality level as 4 Sigma. He set a new target; to achieve the standard of 6 Sigma. Over several years, quality levels improved to 5.5 Sigma, saving Motorola a reported US$2.2 billion. Other US manufacturing companies began to adopt Six Sigma, but it was not until General Electric in the mid-1990s adopted it that it truly began to take shape as a management system. Since then, Six Sigma has spread to European manufacturing companies.

6 Sigma at GE
“6 Sigma – The Breakthrough Strategy, is the most important initiative GE has ever taken…it is part of the genetic code of our future leadership.”
Jack Welch, former CEO, GE

Once the world’s most successful business, the US company GE applied the principles of Six Sigma for years. Its former chief executive Jack Welch regarded it as the most important initiative that GE ever took.

Who kickstarted the Process Improvement Movement?
W. Edwards Deming^[6] is considered one of the pioneers of the process improvement movement. He is known for his work in promoting quality management and statistical process control in manufacturing and business practices. His teachings and ideas have been influential in the development of various quality management methodologies, including Six Sigma. Deming’s 14 Points for Management, which he introduced in the 1980s, are widely regarded as the foundation of modern quality management.

Deming’s 14 Points for Management are a set of principles aimed at improving an organisation’s quality and competitiveness. The 14 points are:

• Create constancy of purpose toward improvement of product and service.
• Adopt a new philosophy.
• Cease dependence on mass inspection.
• End the practice of awarding business on price tag alone; instead, minimise total cost.
• Improve constantly and forever every process for planning, production and service.
• Institute training on the job.
• Institute leadership.
• Drive out fear.
• Break down barriers between staff areas.
• Eliminate slogans, exhortations, and targets for the workforce.
• Eliminate numerical quotas for the workforce and numerical goals for management.
• Remove barriers that rob people of pride in workmanship, and eliminate the annual rating or merit system.
• Institute a vigorous program of education and self-improvement for everyone.
• Put everybody in the company to work to accomplish the transformation.

Benefits of Six Sigma
Often, a management team takes an insider view of the business based on average measures of recent interaction with customers. Customers don’t judge a business on averages – they feel the variance in each transaction. Six Sigma focuses first on reducing process variation and then on improving the process capability. Its benefits are:

• Productivity increases
• Cycle time reduction
• Higher throughput
• Reduced defects
• High levels of outgoing quality
• Standardised improvement methodology across the organisation
• A set of techniques and tools to simplify improvement efforts
• Greater customer satisfaction
• Dramatic improvement in the “bottom-line”.

Key Concepts
The goal of Six Sigma is “Bottom-line” financial improvement. At its core, it revolves around a few key concepts:

• Critical to Quality: the attributes most important to the customer.
• Defect: failing to deliver what the customer wants.
• Process Capability: what your process can deliver.
• Variation: what the customer sees and feels.
• Stable Operations: ensuring consistent, predictable processes to improve what the customer sees and feels.
• Design for Six Sigma: designing to meet customer needs and process capability.

How Does it Work?
Six Sigma is founded on a statistical approach, which assumes that a business comprises a system of interconnected processes. It is systematic, scientific and fact-based. As a closed-loop process, it eliminates unproductive steps, often focuses on new measurements, and applies technology for improvement. Each process contains variations (defects), and all these variations have a cause.

“If I had to reduce my message to management to just a few words, I’d say that it all had to do with reducing variations.”
W. Edwards Deming

At the heart of Six Sigma is an improvement process methodology based on five successive steps (DMAIC), which is an anacronym for:

Comparisons with Other Initiatives
Six Sigma is complementary to other initiatives such as ISO 9000 registration, which is mainly procedural; Total Quality Management (TQM), which is predominantly cultural and Statistical Process Control (SPC), which is primarily statistical process control monitoring. These initiatives attempt to improve quality levels but typically reach a plateau. The Six Sigma approach goes to the next level by recognising that improved quality is a means to an end – but not the end itself.

Lean manufacturing compared with Six Sigma
Both support the reduction of waste in businesses. Lean manufacturing focuses on ‘making value flow’, i.e. providing an easy-to-follow, uninterrupted product flow with minimal waste. Six Sigma focuses on variation-related or lack of process knowledge-related waste such as quality issues, tampering leading to amplified variation in the product delivery process etc.  If applied in an integrated fashion, the tools are complementary and should be used in a ‘hand and glove’ approach.

There are multiple implementation methods for Six Sigma. The appropriate method that drives an organisation’s highest return on investment depends largely on the business and the business environment in which it operates.

The following questions are worth considering before deciding on the appropriate implementation model:

• What performance level is the organisation currently achieving?
• What is the goal for performance?
• What is the required time frame?
• Which level of the organisation is supporting the initiative?
• What kinds of results are targeted?
• What kind of talent is available in the organisation?
• How concentrated will the effort be?
• What are the key leverage points in the organisation?
• What are the key business metrics for the organisation?
• Which implementation method best supports breakthrough improvements for those metrics?
• What is the budget (monetary as well as resource-related)?

The Breakthrough Strategy

Six Sigma in Service Businesses
Quality in a service business means minimum process cycle times, high customer satisfaction ratings, timeliness and accuracy of reports and their delivery, problem free service delivery, reliable processes and order fulfilment, smooth back-office systems etc. Any variation from the target value of service processes costs money. The Six Sigma methodology improves the process of service delivery so that it is focused on this target as close as possible to minimise cost.

In today’s intensely competitive economy, only breakthrough strategies can yield the results shareholders demand. The single most important determination of executive and organisational success lies in the ability to transform existing business strategies and lead an organisation that can create innovative new strategies effectively. There are eight fundamental stages in applying the Breakthrough Strategy to achieve Six Sigma performance:

1. Recognition
2. Definition
3. Measurement
4. Analysis
5. Improvement
6. Control
7. Standardisation
8. Integration.

Each stage is designed to ensure that:

• Companies apply the Breakthrough Strategy in a methodical and disciplined way.
• Six Sigma projects are correctly defined and executed.
• The results of these projects are incorporated into the day-to-day business.

The Breakthrough Strategy applies at each level achieving different yet complementary results. Success at each level is defined to the extent of the improvement in the organisation’s quality and profitability. The Breakthrough Strategy is a fluid methodology that works its way up and down the hierarchies of an organisation. This is one of the reasons Six Sigma needs to be understood and integrated at every company level.

Six Sigma is focused on driving business results. Compared to many other initiatives, it is not a training program with the hope for increased productivity in the future, but rather it focuses on driving business results directly. Projects and candidates are specifically selected to accelerate business performance. Training is provided as a means to drive business results versus being a means of its own. Thus, Six Sigma is different to other initiatives:

• The initiative is business-focused, not quality-focused.
• The leadership is Committed, Competent, and Involved.
• The methodology and tools are data-driven and statistically validated.
• The best people in the organisation are 100% dedicated to defect reduction.
• The focus is on specific projects.
• Provision of a common language to global companies.

Training
Several organisations throughout the UK now provide specific and tailored training on understanding the Six Sigma process and the use of six sigma tools. The student will be trained in the methodology and tools used through real projects with bottom-line impact on the firm’s profitability. A list of training organisations is provided next, but an organisation needs to check their suitability thoroughly.

Training Organisations

• www.isixsigma.com/co/six_sigma
• www.sixsigma.co.uk/training.html
• www.minitab.com/Ltd/sigma_training.htm
• www.papiliolimited.com
• www.smallpeice.co.uk
• www.6sigma-tm.com/SixSigma_main.htm
• www.adamssixsigma.com
• www.sixsigmasystems.com/six_sigma_training.htm
• www.sixsigmascotland.co.uk
• www.statsoft.co.uk/training.html
• www.qualityquest.com/consultancy/6sigma.htm
• http://www.xr-associates.co.uk/qspro_1.html
• http://www.powerdigm.co.uk

Six Sigma Champions

A Six Sigma Champion is usually a top executive or senior manager who “talks the talk” and “walks the walk” of Six Sigma. They are the catalyst and driving force behind an organisation’s Six Sigma implementation. Six Sigma champions are used in many organisations to provide ‘program management’. Champions support project and candidate selection and handle any administrative, reporting-related activity. They act as an interface to operational leadership.

Tools and Terms
There are various tools and terms used in Six Sigma – they relate primarily to quality. Some of them are:

• Control Chart – Monitors variance in a process over time and alerts the business to unexpected variances which may cause defects.
• Defect Measurement – Accounting for the number or frequency of defects that cause lapses in product or service quality.
• Pareto Diagram – Focuses on efforts or the problems that have the greatest potential for improvement by showing relative frequency and/or size in a descending bar graph. Based on the proven Pareto principle: 20% of the sources cause 80% of any problems.
• Process Mapping – Illustrated description of how things get done, which enables participants to visualise an entire process and identify areas of strength and weaknesses. It helps reduce cycle time and defects while recognising the value of individual contributions.

How to get to the power of Six Sigma

Subir Chowdhury‘s book, The Power of Six Sigma provides:

• an excellent overview that demystifies the key elements of implementing Six Sigma.
• practical guidelines for making it happen.
• a clear explanation of how Six Sigma’s disciplined, customer-focused processes enhance organisational effectiveness and improve bottom line results.
• Root Cause Analysis – The study of the original reason for non-conformance with a process. When the root cause is removed or corrected, the non-conformance will be eliminated.
• Statistical Process Control – The application of statistical methods to analyse data, study and monitor process capability and performance.
• Tree Diagram – Graphically shows any broad goal broken into different levels of detailed actions. It encourages team members to expand their thinking when creating solutions.
• Control – The state of stability, normal variation and predictability. The process of regulating and guiding operations and processes using quantitative data.
• CTQ: Critical to Quality (Critical “Y”) – The element of a process or practice that directly impacts its perceived quality.
• Customer Needs, Expectations – Needs, as defined by customers, which meet their basic requirements and standards.
• Defects – Sources of customer irritation. Defects are costly to both customers and manufacturers or service providers. Eliminating defects provides cost benefits.
• Variance – A change in a process or business practice that may alter its expected outcome.

Examples of Six Sigma Organisations

The Six Sigma Academy
The Breakthrough Strategy® is the centrepiece offering of the Six Sigma Academy. They invented it and perfected it. Their services have evolved to reflect best practices from every client they have worked with. Their services are designed to help corporations smoothly and efficiently deploy the Breakthrough Strategy, to achieve breakthrough improvements in corporate performance.
Source: www.6-sigma.com

The following are just a few examples of organisations successfully implementing Six Sigma. Many other companies and organisations in various industries and regions have also adopted Six Sigma as a way to improve their processes and business results.

USA:

• GE (General Electric)
• Motorola
• Honeywell
• Bank of America
• DuPont

UK:

• British Telecom
• Royal Bank of Scotland
• AstraZeneca
• Shell
• British Airways

Continental Europe:

• Siemens AG
• Daimler AG
• Deutsche Bank
• Nokia
• Philips Electronics

Far East:

• Toyota Motor Corporation
• Sony Corporation
• Samsung Electronics
• Honda Motor Co., Ltd.
• LG Electronics Inc.

Failures in applying Six sigmas: organisations that tried it and it made things worse, not better
It’s difficult to say that Six Sigma has “failed” as an approach, as it has been widely adopted and has been successful for many organisations. However, like any methodology or tool, Six Sigma may not always produce the desired results in every situation. There have been instances where organisations have struggled with the implementation of Six Sigma for various reasons, such as:

• Lack of executive commitment and buy-in: Six Sigma requires strong leadership support and commitment from top executives, as well as adequate resources and budget allocation, to be successful.
• Resistance to change: Change can be difficult for some employees, especially those unfamiliar with Six Sigma or who have difficulty adapting to new methods.
• Inadequate training: Six Sigma requires well-trained personnel at all levels of the organisation. If employees are not adequately trained, they may not fully understand or be able to implement the methodology properly.
• Lack of focus: Six Sigma projects should be aligned with the organisation’s overall strategy and goals, and focus should be kept on what will bring the most value to the organisation. Without this focus, projects may not produce the desired results.
• Inflexibility: Six Sigma is a structured methodology, but it may not always be appropriate for every situation. Some organisations may find it too rigid or inflexible for their specific needs, which can lead to failure.

The list above provides just a few examples, and in contrast, Six Sigma has been successful for many organisations. The key to success with Six Sigma is to ensure proper implementation, which includes a commitment to continuous improvement, clear goals and objectives, adequate training and resources, and strong leadership support.

Getting Advice
There are many resources available for organisations looking to become Six Sigma companies. Here are a few places you can go for advice:

Tools from the Juran Institute
The Juran Institute (www.juran.com) provides a wide range of training, consulting services and products developed to improve an organisation’s business performance by focusing on improving and re-engineering the quality of goods, services, and processes. Some of the tools they provide are:

The Six Sigma Basic Training Kit is a complete, six-step program for familiarising your organisation’s improvement teams with Six Sigma.

How To Design Six Sigma Quality Into Products And Services – a 125-page reference guide containing all the basics steps for anyone going through training in breakthrough design/planning.

Six Sigma Improvement Breakthrough is a systematic methodology for creating sustained improvements to Six Sigma levels in important production and repetitive processes.

• Online Resources: There are many online resources available, such as websites, blogs, and forums, that provide information and advice on how to implement Six Sigma in your organisation. Some popular Six Sigma websites include SixSigma.us, iSixSigma, and Six Sigma Daily.
• Six Sigma Consultants: Many consultants specialise in Six Sigma and can help you with everything from planning and implementation to training and continuous improvement. You can find consultants by searching online or through professional organisations, such as the Institute of Management.
• Six Sigma Networking Groups: Joining Six Sigma networking groups can be a great way to connect with other professionals interested in Six Sigma, learn from their experiences, and share your own. You can find these groups online or through professional organisations.
• Six Sigma Tools and Software Providers: Many software and tool providers offer Six Sigma-related products and services, such as Minitab, JMP, and QI Macros. These providers can help you with data analysis and process improvement, among other things.
• Six Sigma Training and Certification Providers: Many organisations offer Six Sigma training and certification, such as the American Society for Quality (ASQ) and the International Association for Six Sigma Certification (IASSC). They can provide training, certification, and support to help you implement Six Sigma in your organisation.

The above are just a few examples of the many resources available to help organisations implement Six Sigma. Organisations need to take the time to research and understand the best approach for them and to seek out the help and resources they need to ensure successful implementation.

Six Sigma in the UK
In the UK, Six Sigma certification is highly sought after by many businesses, including global and blue-chip companies, such as BAE Systems, The Very Group, and Unipart Group. Six Sigma certification can help enhance skills, advance the career of practitioners of the method, and increase their salary.

There are four types of Six Sigma certification in the UK: Yellow Belt, Green Belt, Black Belt, and Master Black Belt. Yellow Belt provides a base level of knowledge, while Green and Black Belt build on this to show how to launch and lead Six Sigma projects. Master Black Belt is the highest certification level, requiring extensive experience and expertise in Six Sigma. All courses include exams.

There is not a single standardised body that issues Six Sigma certification in the UK, but some of the most recognised institutes are:

• Leanscape, which offers online and in-person courses that are accredited by the Council for Six Sigma Certification and the International Association for Six Sigma Certification. Leanscape has worked with some of the biggest names in the industry, such as Google, Amazon, and HSBC.
• Six Sigma UK, which offers online and classroom courses that are accredited by the British Quality Foundation and the Royal Statistical Society. Six Sigma UK has trained over 10,000 professionals and has a high success rate in graduates.
• The Knowledge Academy, which offers online and classroom courses that are accredited by the International Association for Six Sigma Certification and the Lean Six Sigma Society of Professionals. The Knowledge Academy has a global presence and a network of experienced trainers.

Quality Management^[7]
A key innovation of Six Sigma involves professionalising quality management. Before Six Sigma, quality management was largely relegated to the production floor and to statisticians in a separate quality department. Formal Six Sigma programs adopt an elite ranking terminology similar to martial arts systems like judo to define a hierarchy (and career path) that spans business functions and levels.

Six Sigma identifies several roles for successful implementation^[8]:

• Executive Leadership includes the CEO and other members of top management. They are responsible for setting up a vision for Six Sigma implementation. They also empower other stakeholders with the freedom and resources to transcend departmental barriers and overcome resistance to change.^[9]
• Champions take responsibility for Six Sigma implementation across the organisation. The Executive Leadership draws them from upper management. Champions also act as mentors to Black Belts.
• Master Black Belts, identified by Champions, act as in-house coaches on Six Sigma. They devote all their time to Six Sigma, assisting Champions and guiding Black Belts and Green Belts. In addition to statistical tasks, they ensure that Six Sigma is applied consistently across departments and job functions.
• Black Belts operate under Master Black Belts to apply Six Sigma to specific projects. They also devote all their time to Six Sigma. They primarily focus on Six Sigma project execution and special leadership with special tasks, whereas Champions and Master Black Belts focus on identifying projects/functions for Six Sigma.
• Green Belts are the employees who take up Six Sigma implementation along with their other job responsibilities, operating under the guidance of Black Belts.

According to proponents, special training is needed for all of the above practitioners to ensure they follow the methodology and use the data-driven approach correctly.^[10]

Some organisations use additional belt colours, such as “Yellow belts” for employees with basic training in Six Sigma tools and generally participate in projects, and “White belts” for those locally trained in the concepts but do not participate in the project team. “Orange belts” are also mentioned to be used for special cases.^[11]

Six Sigma Articles and Web Resources
General Electric, the giant US corporation which popularised Six Sigma as a result of its outstanding success under the leadership of its CEO Jack Welch, has published very useful information on the subject at www.ge.com/sixsigma

Other resources you may find useful are:

• Free Lean Six Sigma Resources by Six Sigma Global Institute. This web page offers several free Lean Six Sigma resources, such as videos and informative articles, for professionals interested in learning more about quality and process improvement. It covers topics such as Lean Six Sigma basics, tools, case studies, and certification. The URL is https://www.6sigmacertificationonline.com/lean-six-sigma-resources/
• Lean and Six Sigma Articles by 6 Sigma. This web page provides a collection of Lean and Six Sigma articles written by experts and practitioners covering various aspects and applications of the methodologies. It covers topics such as Six Sigma history, benefits, challenges, tools, techniques, and examples. The URL is https://www.6sigma.us/six-sigma-articles.php
• Check our Free Six Sigma Resources by Six Sigma UK. This web page offers a range of free Six Sigma resources, such as guides, templates, calculators, and glossaries, that can help with Six Sigma training and implementation. It covers topics such as Six Sigma principles, roles, phases, tools, and techniques. The URL is https://www.sixsigma.co.uk/resources
• Six Sigma – Overview, Principles, and Methodology by Corporate Finance Institute. This web page provides a comprehensive overview of Six Sigma, its principles, and its methodology. It covers topics such as Six Sigma history, objectives, benefits, levels, roles, and methods. It also explains the difference between Six Sigma and Lean Six Sigma. The URL is https://corporatefinanceinstitute.com/resources/management/six-sigma/
• iSixSigma: Six Sigma Resources for Six Sigma Quality by iSixSigma. This web page is a portal for Six Sigma resources, such as articles, blogs, forums, webinars, podcasts, and events, that cater to Six Sigma quality professionals. It covers topics such as Six Sigma basics, best practices, case studies, trends, and news. The URL is https://www.isixsigma.com/
• Understanding Six Sigma: A Comprehensive Guide to Quality Improvement by PECB. This web page is a comprehensive guide to Six Sigma, its origins, benefits, and its implementation. It covers topics such as Six Sigma history, philosophy, goals, methods, tools, and techniques. It also provides tips and advice on how to achieve Six Sigma certification. The URL is https://pecb.com/article/understanding-six-sigma-a-comprehensive-guide-to-quality-improvement

Glossary

ACRONYMS & TERMS – THEIR MEANING

Reflections
As this paper says, Six Sigma is a methodology used to improve the quality and efficiency of a process by identifying and removing the causes of defects and minimising variability in the process. It was originally developed by Motorola in the mid-1980s and has since been adopted by many organisations in many and various industries.

The term “six sigma” refers to a statistical measure of process variation, and in the Six Sigma methodology, it is used to represent a target level of quality performance. The goal of Six Sigma is to achieve a process performance level of 3.4 defects per million opportunities (DPMO), which translates to a 99.99966% defect-free rate.

As I’ve said, the Six Sigma methodology typically involves five phases: Define, Measure, Analyze, Improve, and Control (DMAIC). These phases systematically identify and eliminate defects, improve process efficiency, and sustain the gains made through continuous monitoring and improvement.

Why Organisations should consider Six Sigma
Six Sigma can help organisations improve operational efficiency, reduce costs, and increase customer satisfaction. Its methodology has been widely adopted in industries such as manufacturing, healthcare, and finance but can be applied to any process where quality improvement is needed.

Accounting and Law
Six Sigma has been applied in a variety of fields, including accounting and law. While it may be more commonly associated with manufacturing and other industrial settings, the principles and methods of Six Sigma can be applied to improve quality and efficiency in a wide range of industries and professions.

• In the case of accounting, for example, Six Sigma can be used to improve the accuracy and timeliness of financial reporting, reduce errors in billing and collections, or streamline internal processes related to accounts payable or payroll. This could involve using statistical analysis tools to identify the root cause of errors and implementing process improvements to prevent them from occurring in the future.
• Similarly, Six Sigma can be used in the legal field to improve the efficiency of contract review, reduce document preparation errors, improve the quality of legal research and analysis, and identify and eliminate bottlenecks and unnecessary steps.

In fact, there are several Six Sigma certification programs specifically geared toward professionals in the fields of accounting and law. These programs provide training and education on the principles and methods of Six Sigma, as well as practical examples of how it can be applied in specific contexts.

Examples of accounting and law firms that have applied Six Sigma methodologies in their operations:

• Deloitte is one of the world’s largest accounting and consulting firms, and it has incorporated Six Sigma methodologies into its operations to improve process efficiency and reduce errors. For example, Deloitte has used Six Sigma to streamline its tax preparation process, improve financial reporting accuracy, and reduce internal control errors.
• PwC is another large accounting and consulting firm that has implemented Six Sigma methodologies in its operations. PwC has used Six Sigma to improve the quality and efficiency of its auditing process, reduce billing errors, and streamline its internal operations.
• GE Capital is a financial services division of General Electric and has been a leader in implementing Six Sigma methodologies in its operations. GE Capital has used Six Sigma to improve the accuracy and timeliness of its financial reporting, reduce costs, and improve customer satisfaction.
• Skadden, Arps, Slate, Meagher & Flom (Scadden) is a global law firm that has applied Six Sigma methodologies to improve the efficiency and quality of its legal operations. For example, Skadden has used Six Sigma to improve its document review process accuracy, streamline its due diligence procedures, and reduce errors in its legal research.
• Seyfarth Shaw is a law firm recognised for its use of Six Sigma methodologies to improve the efficiency and quality of its legal services. The firm has used Six Sigma to improve the accuracy and consistency of its legal drafting, reduce errors in contract review, and streamline its internal operations.

Physicians
Six Sigma can be used in healthcare to improve patient care, reduce medical errors, and increase efficiency in operations. For example, a hospital or GP practice might use Six Sigma to improve patient satisfaction scores, reduce wait times for tests and procedures, and eliminate errors in medication administration.

To Conclude
Six Sigma has already been successfully applied in healthcare, with many hospitals and healthcare providers adopting Six Sigma methodologies to improve their operations and patient outcomes. For example, the Cleveland Clinic, one of the largest and most respected healthcare systems in the United States, has implemented Six Sigma methodologies to improve the quality of patient care and reduce medical errors. The Arizona Diamondbacks, a Major League Baseball team, have also used Six Sigma to improve their operations, reducing concession wait times and increasing sales revenue.

So, while Six Sigma was initially developed for manufacturing processes, it has proven to be a versatile and effective methodology that can be applied to many different fields and industries.

I always thought six sigma was a way an organisation discovered how to achieve optimal performance and quality and designed their processes to work in that way only. At its core, Six Sigma is a set of tools and methodologies that organisations can use to improve the quality of their products, services, and processes. Six Sigma aims to reduce variability and defects in these areas to achieve optimal performance and quality. It follows a structured approach to problem-solving and process improvement that involves defining the problem, measuring the current process performance, analysing the data to identify the root causes of defects, improving the process to eliminate the causes of defects, and controlling the process to sustain the improvements over time.

In practice, Six Sigma mostly finds application in large organisations. According to industry consultants like Thomas Pyzdek and John Kullmann, organisations with fewer than 500 employees are less suited to Six Sigma or need to adapt the standard approach for it to work for them. However, Six Sigma has many tools and techniques that work well in small to mid-size organisations. The fact that an organisation is not big enough to afford black belts does not diminish its ability to make improvements using this set of tools and techniques. The infrastructure described as necessary to support Six Sigma is a result of the size of the organisation rather than a requirement of Six Sigma itself.^[12]

Many successes arising from the adoption of Six Sigma are chronicled in this paper. But failures should be mentioned too. While there are many advocates for a Six Sigma approach for all the reasons set out in this paper, Six Sigma is not a panacea for all organisational maladies. More than half of projects are unsuccessful: in 2010, the Wall Street Journal^[13] reported that more than 60% of projects fail.

A review of academic literature^[14] found 34 common failure factors in 56 papers on Lean, Six Sigma, and LSS from 1995-2013. Among them were (summarised):

• Lack of top management attitude, commitment, and involvement, and lack of leadership and vision.
• Lack of training and education, lack of resources (financial, technical, human, etc.).
• Poor project selection and prioritisation; weak link to strategic objectives of the organisation.
• Resistance to culture change, poor communication, and lack of consideration of the human factors.
• Lack of awareness of the benefits of Lean/Six Sigma and lack of technical understanding of tools, techniques, and practices.

The ultimate aim of Six Sigma is to achieve a level of performance where the likelihood of a defect or error occurring is extremely low, or “six standard deviations” away from the mean, hence the name “Six Sigma.”

So, Six Sigma is not just about finding optimal performance and equality, but also about designing and implementing a structured approach to achieve and sustain that level of performance over time.

References and Further Information

Books

• Certified Lean Six Sigma White Belt Training: Six Sigma White Belt Certification (Accredited) | Six Sigma White Belt & Seven Basic Tools of Quality Simple and Easy!, by Sobia Publication (9 January 2023), available at: https://www.amazon.co.uk/Certified-Lean-Sigma-White-Training-ebook/dp/B0BS1NCYYV
• Essential Guide to Lean Six Sigma & Business Improvement: The secrets every leader or manager should know; a practical roadmap to successful cultural and business change through Lean Six Sigma, by John Wellwood (10 May 2021), available at: https://www.amazon.co.uk/Essential-Guide-Sigma-Business-Improvement/dp/B094N5CWLZ/
• Lean & Lean Six Sigma: For Project Management: 5 (Management Success), by Peter Oliver and Concise Reads (9 April 2018), available at: https://www.amazon.co.uk/Lean-Six-Sigma-Project-Management/dp/1980779244/
• Lean Six Sigma – Green Belt Handbook, by Shweta Ravi (24 July 2017), available at: https://www.amazon.co.uk/Lean-Six-Sigma-Green-Handbook/dp/1521901910/
• Lean Six Sigma and Minitab (7th Edition): The Complete Toolbox Guide for Business Improvement, by Quentin Brook (1 October 2022), available at: https://www.amazon.co.uk/Lean-Six-Sigma-Minitab-7th/dp/0995789959/
• Lean Six Sigma Black Belt Exam Guide 2020 Practice Test Questions & Dumps: 100+ Exam Practice Questions For CSSBB Updated 2020 Paperback, available at: https://www.amazon.co.uk/Sigma-Black-Guide-Practice-Questions/dp/B085RQRMDK/
• Lean Six Sigma Journal, by creative journaling (5 January 2023), available at: https://www.amazon.co.uk/Lean-Sigma-Journal-creative-journaling/dp/B0BRM14GXS/
• Lean Six Sigma Notebook: Plan your LSS Project from A to Z, by creative journaling (8 January 2023), available at: https://www.amazon.co.uk/LEAN-SIX-SIGMA-TOOLBOOK-project/dp/B0BHNNZWM4/
• Lean Six Sigma QuickStart Guide: The Simplified Beginner’s Guide To Lean Six Sigma (QuickStart Guides™ – Business), by Benjamin Sweeney (5 September 2014), available at: https://www.amazon.co.uk/Lean-Six-Sigma-QuickStart-Guide-ebook/dp/B00ND9OMXG/
• Lean Six Sigma: 3 Books in 1: The Complete Guide to Implementing Six Sigma Methodology for Continuous Manufacturing Process Improvement (Lean Methodology), by Jeffrey Ries (29 September 2022), available at: https://www.amazon.co.uk/Lean-Six-Sigma-Implementing-Manufacturing/dp/B0BGNC7SZX/
• Lean Six Sigma: Plan your LSS Project from A to Z, by creative journaling (10 October 2022), available at: https://www.amazon.co.uk/Lean-Six-Sigma-Plan-Project/dp/B0BJ4WR7JJ/
• Plan your Lean Six Sigma Project, by creative journaling (9 January 2023), available at: https://www.amazon.co.uk/plan-your-lean-sigma-Project/dp/B0BRYWHZFW/
• Six Sigma For Dummies, 2nd Edition, by Gygi (27 September 2012), available at: https://www.amazon.co.uk/Six-Sigma-Dummies-Craig-Gygi/dp/1118120353/
• Six Sigma Green Belt Study Guide: Prep Book with Practice Test Questions for the ASQ Certification Exam [3rd Edition], by Joshua Rueda (23 May 2022), available at: https://www.amazon.co.uk/Sigma-Green-Belt-Study-Guide/dp/1637751966/
• Six Sigma Notebook: Plan your Lean Six Sigma Projects from A to Z, by creative journaling (28 December 2022), available at: https://www.amazon.co.uk/Six-Sigma-Notebook-Plan-Projects/dp/B0BRDK8L6K
• Six Sigma: A Complete Step-by-Step Guide: A Complete Training & Reference Guide for White Belts, Yellow Belts, Green Belts, and Black Belts, by Council for Six Sigma Certification and Craig Joseph Setter (19 July 2018), available at: https://www.amazon.co.uk/Six-Sigma-Step-Step-Reference/dp/1732592608/
• Six Sigma: Step-by-Step Guide to Six Sigma (Six Sigma Tools, DMAIC, Value Stream Mapping, Launching a Project and Implementing Six Sigma), by Jason Bennett and Jennifer Bowen (12 November 2018), available at: https://www.amazon.co.uk/Six-Sigma-Step-Step-Implementing/dp/1724653148/
• The Lean Six Sigma Pocket Toolbook: A Quick Reference Guide to 100 Tools for Improving Quality and Speed, by Michael L. George (22 September 2004), available at: https://www.amazon.co.uk/Lean-Six-Sigma-Pocket-Toolbook/dp/0071441190/
• The McGraw-Hill 36-Hour Course: Lean Six Sigma (McGraw-Hill 36-Hour Courses), by Sheila Shaffie (30 April 2012), available at: https://www.amazon.co.uk/McGraw-Hill-36-Hour-Course-Sigma-Courses/dp/0071743855

Videos

• Lean Six Sigma In 8 Minutes by Simplilearn. The video explains what Lean Six Sigma is, how it works, and why it is important. It also covers the basics of the Lean Six Sigma methodology and the difference between Lean and Six Sigma. https://www.youtube.com/watch?v=s2HCrhNVfak
• Learn Six Sigma Black Belt – Certification Made Simple by Udemy. This course teaches the skills and knowledge required to become a Six Sigma Black Belt professional. It covers the updated ASQ® CSSBB BoK and includes 18 videos added in July 2022. The course also provides quizzes, assignments, and practice exams. https://www.udemy.com/course/six-sigma-black-belt/
• Six Sigma In 9 Minutes by Simplilearn. This video explains what Six Sigma is, how it works, and why it is important. It also covers the basics of the Six Sigma methodology and the difference between Six Sigma and Lean Six Sigma. https://www.youtube.com/watch?v=4EDYfSl-fmc
• Six Sigma Training Videos [2022 Updated] by Simplilearn. This playlist of 38 videos provides an introduction and overview of Six Sigma, its history, benefits, levels, roles, and methods. The videos are from Simplilearn, a leading provider of Six Sigma certification and training. The videos are about 10 minutes long on average. https://www.youtube.com/playlist?list=PLEiEAq2VkUUIPW1oBXy5PNbdeV1frCQkT
• Six Sigma Training Videos [2022 Updated] by teracourses.com. This is a playlist of 38 videos that cover various topics and concepts of Six Sigma, such as DMAIC, Lean, tools, techniques, case studies, and certification. The videos are from different sources and instructors, and range from 5 minutes to 3 hours in length. https://teracourses.com/ar/course/6-sigma-course3

CAUTION: This paper is compiled from the sources stated but has not been externally reviewed. Parts of this paper include information provided via artificial intelligence which, although checked by the author, is not always accurate or reliable. Neither we nor any third parties provide any warranty or guarantee as to the accuracy, timeliness, performance, completeness or suitability of the information and materials covered in this paper for any particular purpose. Such information and materials may contain inaccuracies or errors and we expressly exclude liability for any such inaccuracies or errors to the fullest extent permitted by law. Your use of any information or materials on this website is entirely at your own risk, for which we shall not be liable. It shall be your own responsibility to ensure that any products, services or information available through this paper meet your specific requirements and you should neither take action nor exercise inaction without taking appropriate professional advice. The hyperlinks were current at the date of publication.

End Notes and Explanations

1. Source: This paper has been compiled from an earlier paper I wrote some years ago, and now updated by further research including machine-generated artificial intelligence at: bing.com [chat] and https://chat.openai.com ↑
2. See article at: Information Week (https://www.informationweek.com/it-life/whatever-happened-to-six-sigma-) ↑

3. Explanation: In 1986, Bill Smith and Mikel Harry, two engineers at Motorola were accredited to having developed “Six Sigma”, and in 1995, Jack Welch made it the central business strategy of General Electric. Source: https://www.sciencedirect.com/topics/computer-science/six-sigma

4. Explanation: Motorola, who hold the Six Sigma trademark, said in 2010 that the data-driven defect-reduction process had saved the company more than $16 billion over the previous 15 years. Six Sigma has generated similarly stunning results at companies here and abroad in the manufacturing, transactional, and service sectors. All businesses – regardless of sector, size, or project – link their success to one factor. In Six Sigma parlance, it is the Black Belt. While the late Bill Smith, a Motorola senior engineer and scientist, commonly gets credit for initiating the Six Sigma concept, the wordsmith who originated the belt argot is Dr Mikel Harry. Excerpted with acknowledgement from: https://www.isixsigma.com/history/history-six-sigma-black-belt-naming-convention/ ↑

5. Explanation: Eliyahu Moshe Goldratt was an Israeli business management guru. He was the originator of the Optimized Production Technique, the Theory of Constraints (TOC), the Thinking Processes, Drum-Buffer-Rope, Critical Chain Project Management and other TOC derived tools. Source: https://en.wikipedia.org/wiki/Eliyahu_M._Goldratt ↑

6. Explanation: Dr William Edwards Deming offered 14 key principles for management to follow to improve the effectiveness of a business or organisation significantly. The principles (points) were first presented in his book Out of the Crisis. (Source: https://deming.org/explore/fourteen-points/). Deming (October 14, 1900 – December 20, 1993) was an American engineer, statistician, professor, author, lecturer, and management consultant. Educated initially as an electrical engineer and later specialising in mathematical physics, he helped develop the sampling techniques still used by the US Department of the Census and the Bureau of Labor Statistics. He is also known as the father of the quality movement and was hugely influential in post-WWII Japan. He is most well-known for his theories of management. Source: https://en.wikipedia.org/wiki/W._Edwards_Deming ↑

7. Source: https://en.wikipedia.org/wiki/Six_Sigma ↑

8. Source: Harry, Mikel; Schroeder, Richard (2000). Six Sigma. Random House, Inc. ISBN 0-385-49437-8. Cited at: https://en.wikipedia.org/wiki/Six_Sigma ↑

9. Source: “Six sigma support from upper management”. 6sigma.us. Cited at: https://en.wikipedia.org/wiki/Six_Sigma ↑

10. Source: Bertels, Thomas (2003) Rath & Strong’s Six Sigma Leadership Handbook. John Wiley and Sons. pp 57–83 ISBN 0-471-25124-0. Cited at: https://en.wikipedia.org/wiki/Six_Sigma ↑

11. Source: Harry, Mikel J.; Mann, Prem S.; De Hodgins, Ofelia C.; Hulbert, Richard L.; Lacke, Christopher J. (20 September 2011). Practitioner’s Guide to Statistics and Lean Six Sigma for Process Improvements. John Wiley and Sons. pp. 30–. ISBN 978-1-118-21021-5. Cited at: https://en.wikipedia.org/wiki/Six_Sigma ↑

12. Source: https://www.qualitydigest.com/nov01/html/sixsigmaarticle.html Cited at: https://en.wikipedia.org/wiki/Six_Sigma ↑

13. Source: https://www.wsj.com/articles/SB10001424052748703298004574457471313938130 ↑

14. Source:  Albliwi, S.; Antony, J.; Halim Lim, S.A.; van der Wiele, T. (2014). “Critical failure factors of Lean Six Sigma: a systematic literature review”.  International Journal of Quality & Reliability Management. 31 (9): 1012–1030. doi:10.1108/IJQRM-09-2013-0147. Cited at: https://en.wikipedia.org/wiki/Six_Sigma ↑