Six Sigma
Encyclopedia
Six Sigma is a business management strategy
Strategic management
Strategic management is a field that deals with the major intended and emergent initiatives taken by general managers on behalf of owners, involving utilization of resources, to enhance the performance of firms in their external environments...
originally developed by Motorola
Motorola
Motorola, Inc. was an American multinational telecommunications company based in Schaumburg, Illinois, which was eventually divided into two independent public companies, Motorola Mobility and Motorola Solutions on January 4, 2011, after losing $4.3 billion from 2007 to 2009...
, USA in 1986. , it is widely used in many sectors of industry.
Six Sigma seeks to improve the quality of process outputs by identifying and removing the causes of defects (errors) and minimizing variability
Statistical dispersion
In statistics, statistical dispersion is variability or spread in a variable or a probability distribution...
in manufacturing
Manufacturing
Manufacturing is the use of machines, tools and labor to produce goods for use or sale. The term may refer to a range of human activity, from handicraft to high tech, but is most commonly applied to industrial production, in which raw materials are transformed into finished goods on a large scale...
and business process
Business process
A business process or business method is a collection of related, structured activities or tasks that produce a specific service or product for a particular customer or customers...
es. It uses a set of quality management
Quality management
The term Quality management has a specific meaning within many business sectors. This specific definition, which does not aim to assure 'good quality' by the more general definition , can be considered to have four main components: quality planning, quality control, quality assurance and quality...
methods, including statistical methods
Statistics
Statistics is the study of the collection, organization, analysis, and interpretation of data. It deals with all aspects of this, including the planning of data collection in terms of the design of surveys and experiments....
, and creates a special infrastructure of people within the organization ("Black Belts", "Green Belts", etc.) who are experts in these methods. Each Six Sigma project carried out within an organization follows a defined sequence of steps and has quantified financial targets (cost reduction and/or profit increase).
The term Six Sigma originated from terminology associated with manufacturing, specifically terms associated with statistical modeling of manufacturing processes
Process capability
A process is a unique combination of tools, materials, methods, and people engaged in producing a measurable output; for example a manufacturing line for machine parts...
. The maturity of a manufacturing process can be described by a sigma rating indicating its yield, or the percentage of defect-free products it creates. A six sigma process is one in which 99.99966% of the products manufactured are statistically expected to be free of defects (3.4 defects per million). Motorola set a goal of "six sigma" for all of its manufacturing operations, and this goal became a byword for the management and engineering practices used to achieve it.
Historical overview
Six Sigma originated as a set of practices designed to improve manufacturing processIndustrial process
Industrial processes are procedures involving chemical or mechanical steps to aid in the manufacture of an item or items, usually carried out on a very large scale. Industrial processes are the key components of heavy industry....
es and eliminate defects, but its application was subsequently extended to other types of business processes as well.
In Six Sigma, a defect is defined as any process output that does not meet customer specifications, or that could lead to creating an output that does not meet customer specifications.
The core of Six Sigma was “born” at Motorola
Motorola
Motorola, Inc. was an American multinational telecommunications company based in Schaumburg, Illinois, which was eventually divided into two independent public companies, Motorola Mobility and Motorola Solutions on January 4, 2011, after losing $4.3 billion from 2007 to 2009...
in the 1970s out of senior executive Art Sundry's criticism of Motorola’s bad quality. As a result of this criticism, the company discovered a connection between increases in quality and decreases in costs of production. At that time, the prevailing view was that quality costs extra money. In fact, it reduced total costs by driving down the costs for repair or control. Bill Smith
Bill Smith (Motorola engineer)
Bill Smith is the "Father of Six Sigma". Born in Brooklyn, New York, Smith graduated from the U.S. Naval Academy in 1952 and studied at the University of Minnesota School of Management...
subsequently formulated the particulars of the methodology at Motorola
Motorola
Motorola, Inc. was an American multinational telecommunications company based in Schaumburg, Illinois, which was eventually divided into two independent public companies, Motorola Mobility and Motorola Solutions on January 4, 2011, after losing $4.3 billion from 2007 to 2009...
in 1986. Six Sigma was heavily inspired by the quality improvement methodologies of the six preceding decades, such as quality control
Quality control
Quality control, or QC for short, is a process by which entities review the quality of all factors involved in production. This approach places an emphasis on three aspects:...
, Total Quality Management
Total Quality Management
Total quality management or TQM is an integrative philosophy of management for continuously improving the quality of products and processes....
(TQM), and Zero Defects
Zero Defects
"Zero Defects" is Step 7 of "Philip Crosby's 14 Step Quality Improvement Process" . Although applicable to any type of enterprise, it has been primarily adopted within industry supply chains wherever large volumes of components are being purchased .Zero Defects was a quality control program...
, based on the work of pioneers such as Shewhart
Walter A. Shewhart
Walter Andrew Shewhart March 18, 1891 - March 11, 1967) was an American physicist, engineer and statistician, sometimes known as the father of statistical quality control.W...
, Deming
W. Edwards Deming
William Edwards Deming was an American statistician, professor, author, lecturer and consultant. He is perhaps best known for his work in Japan...
, Juran
Joseph M. Juran
Joseph Moses Juran was a 20th century management consultant who is principally remembered as an evangelist for quality and quality management, writing several influential books on those subjects. He was the brother of Academy Award winner Nathan H...
, Ishikawa
Kaoru Ishikawa
was a Japanese university professor and influential quality management innovator best known in North America for the Ishikawa or cause and effect diagram that is used in the analysis of industrial process.- Biography :...
, Taguchi
Genichi Taguchi
is an engineer and statistician. From the 1950s onwards, Taguchi developed a methodology for applying statistics to improve the quality of manufactured goods...
and others.
Like its predecessors, Six Sigma doctrine asserts that:
- Continuous efforts to achieve stable and predictable process results (i.e., reduce process variationStatistical dispersionIn statistics, statistical dispersion is variability or spread in a variable or a probability distribution...
) are of vital importance to business success. - Manufacturing and business processes have characteristics that can be measured, analyzed, improved and controlled.
- Achieving sustained quality improvement requires commitment from the entire organization, particularly from top-level management.
Features that set Six Sigma apart from previous quality improvement initiatives include:
- A clear focus on achieving measurable and quantifiable financial returns from any Six Sigma project.
- An increased emphasis on strong and passionate management leadership and support.
- A special infrastructure of "Champions," "Master Black Belts," "Black Belts," "Green Belts", etc. to lead and implement the Six Sigma approach.
- A clear commitment to making decisions on the basis of verifiable data, rather than assumptions and guesswork.
The term "Six Sigma" comes from a field of statistics known as process capability
Process capability
A process is a unique combination of tools, materials, methods, and people engaged in producing a measurable output; for example a manufacturing line for machine parts...
studies. Originally, it referred to the ability of manufacturing processes to produce a very high proportion of output within specification. Processes that operate with "six sigma quality" over the short term are assumed to produce long-term defect levels below 3.4 defects per million opportunities
Defects per million opportunities
In process improvement efforts, defects per million opportunities or DPMO is a measure of process performance. It is defined as...
(DPMO). Six Sigma's implicit goal is to improve all processes to that level of quality or better.
Six Sigma is a registered service mark
Service mark
A service mark or servicemark is a trademark used in some countries, notably the United States, to identify a service rather than a product. When a service mark is federally registered, the standard registration symbol ® or "Reg U.S. Pat & TM Off" may be used...
and trademark of Motorola
Motorola
Motorola, Inc. was an American multinational telecommunications company based in Schaumburg, Illinois, which was eventually divided into two independent public companies, Motorola Mobility and Motorola Solutions on January 4, 2011, after losing $4.3 billion from 2007 to 2009...
Inc. Motorola reported over US$17 billion in savings from Six Sigma. Other early adopters of Six Sigma who achieved well-publicized success include Honeywell
Honeywell
Honeywell International, Inc. is a major conglomerate company that produces a variety of consumer products, engineering services, and aerospace systems for a wide variety of customers, from private consumers to major corporations and governments....
(previously known as AlliedSignal
AlliedSignal
AlliedSignal was an aerospace, automotive and engineering company that acquired and merged with Honeywell for $15 billion in 1999, after which the new group adopted the Honeywell name.AlliedSignal was created through a 1985 merger of Allied Corp...
) and General Electric
General Electric
General Electric Company , or GE, is an American multinational conglomerate corporation incorporated in Schenectady, New York and headquartered in Fairfield, Connecticut, United States...
, where Jack Welch
Jack Welch
John Francis "Jack" Welch, Jr. is an American chemical engineer, business executive, and author. He was Chairman and CEO of General Electric between 1981 and 2001...
introduced the method. By the late 1990s, about two-thirds of the Fortune 500
Fortune 500
The Fortune 500 is an annual list compiled and published by Fortune magazine that ranks the top 500 U.S. closely held and public corporations as ranked by their gross revenue after adjustments made by Fortune to exclude the impact of excise taxes companies collect. The list includes publicly and...
organizations had begun Six Sigma initiatives with the aim of reducing costs and improving quality.
In , some practitioners have combined Six Sigma ideas with lean manufacturing
Lean manufacturing
Lean manufacturing, lean enterprise, or lean production, often simply, "Lean," is a production practice that considers the expenditure of resources for any goal other than the creation of value for the end customer to be wasteful, and thus a target for elimination...
to create a methodology named Lean Six Sigma. The Lean Six Sigma methodology views lean manufacturing, which addresses process flow and waste issues, and Six Sigma, with its focus on variation and design, as complementary disciplines aimed at promoting "business and operational excellence". Companies such as IBM use Lean Six Sigma to focus transformation efforts not just on efficiency but also on growth. It serves as a foundation for innovation throughout the organization, from manufacturing and software development to sales and service delivery functions.
Methods
Six Sigma projects follow two project methodologies inspired by DemingW. Edwards Deming
William Edwards Deming was an American statistician, professor, author, lecturer and consultant. He is perhaps best known for his work in Japan...
's Plan-Do-Check-Act Cycle
PDCA
PDCA is an iterative four-step management method used in business for the control and continuous improvement of processes and products...
. These methodologies, composed of five phases each, bear the acronyms DMAIC and DMADV.
- DMAIC is used for projects aimed at improving an existing business process. DMAIC is pronounced as "duh-may-ick".
- DMADV is used for projects aimed at creating new product or process designs. DMADV is pronounced as "duh-mad-vee".
DMAIC
The DMAIC project methodology has five phases:- Define the problem, the voice of the customer, and the project goals, specifically.
- Measure key aspects of the current process and collect relevant data.
- Analyze the data to investigate and verify cause-and-effect relationships. Determine what the relationships are, and attempt to ensure that all factors have been considered. Seek out root cause of the defect under investigation.
- Improve or optimize the current process based upon data analysis using techniques such as design of experimentsDesign of experimentsIn general usage, design of experiments or experimental design is the design of any information-gathering exercises where variation is present, whether under the full control of the experimenter or not. However, in statistics, these terms are usually used for controlled experiments...
, poka yoke or mistake proofing, and standard work to create a new, future state process. Set up pilot runs to establish process capabilityProcess capabilityA process is a unique combination of tools, materials, methods, and people engaged in producing a measurable output; for example a manufacturing line for machine parts...
. - Control the future state process to ensure that any deviations from target are corrected before they result in defects. Implement control systems such as statistical process controlStatistical process controlStatistical process control is the application of statistical methods to the monitoring and control of a process to ensure that it operates at its full potential to produce conforming product. Under SPC, a process behaves predictably to produce as much conforming product as possible with the least...
, production boards , visual workplaces, and continuously monitor the process.
DMADV or DFSS
The DMADV project methodology, also known as DFSS ("Design For Six Sigma"), features five phases:- D
Quality management tools and methods used in Six Sigma
Within the individual phases of a DMAIC or DMADV project, Six Sigma utilizes many established quality-management tools that are also used outside of Six Sigma. The following table shows an overview of the main methods used.- 5 Whys5 WhysThe 5 Whys is a questions-asking method used to explore the cause/effect relationships underlying a particular problem. Ultimately, the goal of applying the 5 Whys method is to determine a root cause of a defect or problem.- Example :...
- Accelerated life testingAccelerated life testingAccelerated life testing is the process of testing a product by subjecting it to conditions in excess of its normal service parameters in an effort to uncover faults and potential modes of failure in a short amount of time...
- Analysis of varianceAnalysis of varianceIn statistics, analysis of variance is a collection of statistical models, and their associated procedures, in which the observed variance in a particular variable is partitioned into components attributable to different sources of variation...
- ANOVA Gauge R&R
- Axiomatic designAxiomatic designAxiomatic design is a systems design methodology using matrix methods to systematically analyze the transformation of customer needs into functional requirements, design parameters, and process variables....
- Business Process MappingBusiness Process MappingBusiness process mapping refers to activities involved in defining exactly what a business entity does, who is responsible, to what standard a process should be completed and how the success of a business process can be determined. Once this is done, there can be no uncertainty as to the...
- Cause & effects diagram (also known as fishbone or Ishikawa diagramIshikawa diagramIshikawa diagrams are causal diagrams that show the causes of a certain event -- created by Kaoru Ishikawa . Common uses of the Ishikawa diagram are product design and quality defect prevention, to identify potential factors causing an overall effect...
) - Check sheetCheck sheetThe check sheet is a simple document that is used for collecting data in real-time and at the location where the data is generated. The document is typically a blank form that is designed for the quick, easy, and efficient recording of the desired information, which can be either quantitative or...
- Chi-squared test of independence and fits
- Control chartControl chartControl charts, also known as Shewhart charts or process-behaviour charts, in statistical process control are tools used to determine whether or not a manufacturing or business process is in a state of statistical control.- Overview :...
- CorrelationCorrelationIn statistics, dependence refers to any statistical relationship between two random variables or two sets of data. Correlation refers to any of a broad class of statistical relationships involving dependence....
- Cost-benefit analysisCost-benefit analysisCost–benefit analysis , sometimes called benefit–cost analysis , is a systematic process for calculating and comparing benefits and costs of a project for two purposes: to determine if it is a sound investment , to see how it compares with alternate projects...
- CTQ treeCTQ TreeA CTQ tree is used to decompose broad customer requirements into more easily quantified requirements. CTQ Trees are often used in the Six Sigma methodology....
- Design of experimentsDesign of experimentsIn general usage, design of experiments or experimental design is the design of any information-gathering exercises where variation is present, whether under the full control of the experimenter or not. However, in statistics, these terms are usually used for controlled experiments...
- Failure mode and effects analysisFailure mode and effects analysisA failure modes and effects analysis is a procedure in product development and operations management for analysis of potential failure modes within a system for classification by the severity and likelihood of the failures...
(FMEA) - General linear modelGeneral linear modelThe general linear model is a statistical linear model.It may be written aswhere Y is a matrix with series of multivariate measurements, X is a matrix that might be a design matrix, B is a matrix containing parameters that are usually to be estimated and U is a matrix containing errors or...
- HistogramHistogramIn statistics, a histogram is a graphical representation showing a visual impression of the distribution of data. It is an estimate of the probability distribution of a continuous variable and was first introduced by Karl Pearson...
s
- Pareto analysisPareto analysisPareto analysis is a statistical technique in decision making that is used for selection of a limited number of tasks that produce significant overall effect. It uses the Pareto principle – the idea that by doing 20% of work, 80% of the advantage of doing the entire job can be generated...
- Pareto chart
- Pick chartPick chartA PICK chart is a Lean Six Sigma tool, developed by Lockheed Martin, for organizing process improvement ideas and categorizing them during the Identify and Prioritize Opportunities Phase of a Lean Six Sigma project.-Use:...
- Process capabilityProcess capabilityA process is a unique combination of tools, materials, methods, and people engaged in producing a measurable output; for example a manufacturing line for machine parts...
- Quality Function DeploymentQuality function deploymentQuality function deployment is a “method to transform user demands into design quality, to deploy the functions forming quality, and to deploy methods for achieving the design quality into subsystems and component parts, and ultimately to specific elements of the manufacturing process.”, as...
(QFD) - Quantitative marketing researchQuantitative marketing researchQuantitative marketing research is the application of quantitative research techniques to the field of marketing. It has roots in both the positivist view of the world, and the modern marketing viewpoint that marketing is an interactive process in which both the buyer and seller reach a satisfying...
through use of Enterprise Feedback ManagementEnterprise Feedback ManagementEnterprise feedback management is a system of processes and software that enables organizations to centrally manage deployment of surveys while dispersing authoring and analysis throughout an organization...
(EFM) systems - Regression analysisRegression analysisIn statistics, regression analysis includes many techniques for modeling and analyzing several variables, when the focus is on the relationship between a dependent variable and one or more independent variables...
- Root cause analysisRoot cause analysisRoot cause analysis is a class of problem solving methods aimed at identifying the root causes of problems or events.Root Cause Analysis is any structured approach to identifying the factors that resulted in the nature, the magnitude, the location, and the timing of the harmful outcomes of one...
- Run chartRun ChartA run chart, also known as a run-sequence plot is a graph that displays observed data in a time sequence. Often, the data displayed represent some aspect of the output or performance of a manufacturing or other business process.- Overview :...
s - Scatter diagram
- SIPOCSIPOCSIPOC is a six sigma tool. The acronym SIPOC stands for Suppliers, inputs, process, outputs, customers. A SIPOC is completed most easily by starting from the right and working towards the left.For example:Suppliers - grocers and vendors...
analysis (Suppliers, Inputs, Process, Outputs, Customers) - StratificationStratified samplingIn statistics, stratified sampling is a method of sampling from a population.In statistical surveys, when subpopulations within an overall population vary, it is advantageous to sample each subpopulation independently. Stratification is the process of dividing members of the population into...
- Taguchi methodsTaguchi methodsTaguchi methods are statistical methods developed by Genichi Taguchi to improve the quality of manufactured goods, and more recently also applied to, engineering, biotechnology, marketing and advertising...
- Taguchi Loss FunctionTaguchi loss functionThe Taguchi Loss Function is a graphical depiction of loss developed by the Japanese business statistician Genichi Taguchi to describe a phenomenon affecting the value of products produced by a company. Praised by Dr. W...
- TRIZTRIZTRIZ is "a problem-solving, analysis and forecasting tool derived from the study of patterns of invention in the global patent literature". It was developed by the Soviet inventor and science fiction author Genrich Altshuller and his colleagues, beginning in 1946...
Implementation roles
One key innovation of Six Sigma involves the "professionalizing" of quality management functions. Prior to Six Sigma, quality management in practice was largely relegated to the production floor and to statisticianStatistician
A statistician is someone who works with theoretical or applied statistics. The profession exists in both the private and public sectors. The core of that work is to measure, interpret, and describe the world and human activity patterns within it...
s in a separate quality department. Formal Six Sigma programs adopt a ranking terminology (similar to some martial arts systems) to define a hierarchy (and career path) that cuts across all business functions.
Six Sigma identifies several key roles for its successful implementation.
- 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 the other role holders with the freedom and resources to explore new ideas for breakthrough improvements.
- Champions take responsibility for Six Sigma implementation across the organization in an integrated manner. 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 100% of their time to Six Sigma. They assist champions and guide Black Belts and Green Belts. Apart from statistical tasks, they spend their time on ensuring consistent application of Six Sigma across various functions and departments.
- Black Belts operate under Master Black Belts to apply Six Sigma methodology to specific projects. They devote 100% of their time to Six Sigma. They primarily focus on Six Sigma project execution, 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.
Some organizations use additional belt colours, such as Yellow Belts, for employees that have 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.
Certification
Corporations such as early Six Sigma pioneers General Electric and Motorola developed certification programs as part of their Six Sigma implementation, verifying individuals' command of the Six Sigma methods at the relevant skill level (Green Belt, Black Belt etc.). Following this approach, many organizations in the 1990s starting offering Six Sigma certifications to their employees. Criteria for Green Belt and Black Belt certification vary; some companies simply require participation in a course and a Six Sigma project. There is no standard certification body, and different certification services are offered by various quality associations and other providers against a fee. The American Society for QualityAmerican Society for Quality
American Society for Quality , formerly known as American Society for Quality Control , is a knowledge-based global community of quality control experts, with nearly 85,000 members dedicated to the promotion and advancement of quality tools, principles, and practices in their workplaces and in...
for example requires Black Belt applicants to pass a written exam and to provide a signed affidavit stating that they have completed two projects, or one project combined with three years' practical experience in the body of knowledge. The International Quality Federation offers an online certification exam that organizations can use for their internal certification programs; it is statistically more demanding than the ASQ certification. Other providers offering certification services include the Juran Institute
Juran Institute
-History:Juran Institute is an international consulting company founded by quality expert Joseph M. Juran in 1979. It provides training and consulting services in quality improvement and Lean management as well as Six Sigma certification....
, Six Sigma Qualtec, Air Academy Associates and others.
Origin and meaning of the term "six sigma process"
The term "six sigma process" comes from the notion that if one has six standard deviationStandard deviation
Standard deviation is a widely used measure of variability or diversity used in statistics and probability theory. It shows how much variation or "dispersion" there is from the average...
s between the process mean
Mean
In statistics, mean has two related meanings:* the arithmetic mean .* the expected value of a random variable, which is also called the population mean....
and the nearest specification limit, as shown in the graph, practically no items will fail to meet specifications. This is based on the calculation method employed in process capability studies
Process capability
A process is a unique combination of tools, materials, methods, and people engaged in producing a measurable output; for example a manufacturing line for machine parts...
.
Capability studies measure the number of standard deviations between the process mean and the nearest specification limit in sigma units. As process standard deviation goes up, or the mean of the process moves away from the center of the tolerance, fewer standard deviations will fit between the mean and the nearest specification limit, decreasing the sigma number and increasing the likelihood of items outside specification.
Role of the 1.5 sigma shift
Experience has shown that processes usually do not perform as well in the long term as they do in the short term. As a result, the number of sigmas that will fit between the process mean and the nearest specification limit may well drop over time, compared to an initial short-term study. To account for this real-life increase in process variation over time, an empirically-based 1.5 sigma shift is introduced into the calculation. According to this idea, a process that fits 6 sigma between the process mean and the nearest specification limit in a short-term study will in the long term fit only 4.5 sigma – either because the process mean will move over time, or because the long-term standard deviation of the process will be greater than that observed in the short term, or both.Hence the widely accepted definition of a six sigma process is a process that produces 3.4 defective parts per million opportunities
Defects per million opportunities
In process improvement efforts, defects per million opportunities or DPMO is a measure of process performance. It is defined as...
(DPMO). This is based on the fact that a process that is normally distributed will have 3.4 parts per million beyond a point that is 4.5 standard deviations above or below the mean (one-sided capability study). So the 3.4 DPMO of a six sigma process in fact corresponds to 4.5 sigma, namely 6 sigma minus the 1.5-sigma shift introduced to account for long-term variation. This allows for the fact that special causes may result in a deterioration in process performance over time, and is designed to prevent underestimation of the defect levels likely to be encountered in real-life operation.
Sigma levels
The tablebelow gives long-term DPMO
Defects per million opportunities
In process improvement efforts, defects per million opportunities or DPMO is a measure of process performance. It is defined as...
values corresponding to various short-term sigma levels.
It must be understood that these figures assume that the process mean will shift by 1.5 sigma toward the side with the critical specification limit. In other words, they assume that after the initial study determining the short-term sigma level, the long-term Cpk value will turn out to be 0.5 less than the short-term Cpk value. So, for example, the DPMO
Defects per million opportunities
In process improvement efforts, defects per million opportunities or DPMO is a measure of process performance. It is defined as...
figure given for 1 sigma assumes that the long-term process mean will be 0.5 sigma beyond the specification limit (Cpk = –0.17), rather than 1 sigma within it, as it was in the short-term study (Cpk = 0.33). Note that the defect percentages indicate only defects exceeding the specification limit to which the process mean is nearest. Defects beyond the far specification limit are not included in the percentages.
| Sigma level | DPMO Defects per million opportunities In process improvement efforts, defects per million opportunities or DPMO is a measure of process performance. It is defined as... |
Percent defective | Percentage yield | Short-term Cpk | Long-term Cpk |
|---|---|---|---|---|---|
| 1 | 691,462 | 69% | 31% | 0.33 | –0.17 |
| 2 | 308,538 | 31% | 69% | 0.67 | 0.17 |
| 3 | 66,807 | 6.7% | 93.3% | 1.00 | 0.5 |
| 4 | 6,210 | 0.62% | 99.38% | 1.33 | 0.83 |
| 5 | 233 | 0.023% | 99.977% | 1.67 | 1.17 |
| 6 | 3.4 | 0.00034% | 99.99966% | 2.00 | 1.5 |
| 7 | 0.019 | 0.0000019% | 99.9999981% | 2.33 | 1.83 |
Application
Six Sigma mostly finds application in large organizations. An important factor in the spread of Six Sigma was GE's 1998 announcement of $350 million in savings thanks to Six Sigma, a figure that later grew to more than $1 billion. According to industry consultants like Thomas Pyzdek and John Kullmann, companies with fewer than 500 employees are less suited to Six Sigma implementation, or need to adapt the standard approach to make it work for them. This is due both to the infrastructure of Black Belts that Six Sigma requires, and to the fact that large organizations present more opportunities for the kinds of improvements Six Sigma is suited to bringing about.Lack of originality
Noted quality expert Joseph M. JuranJoseph M. Juran
Joseph Moses Juran was a 20th century management consultant who is principally remembered as an evangelist for quality and quality management, writing several influential books on those subjects. He was the brother of Academy Award winner Nathan H...
has described Six Sigma as "a basic version of quality improvement", stating that "there is nothing new there. It includes what we used to call facilitators. They've adopted more flamboyant terms, like belts with different colors. I think that concept has merit to set apart, to create specialists who can be very helpful. Again, that's not a new idea. The American Society for Quality
American Society for Quality
American Society for Quality , formerly known as American Society for Quality Control , is a knowledge-based global community of quality control experts, with nearly 85,000 members dedicated to the promotion and advancement of quality tools, principles, and practices in their workplaces and in...
long ago established certificates, such as for reliability engineers."
Role of consultants
The use of "Black Belts" as itinerant change agents has (controversially) fostered an industry of training and certification. Critics argue there is overselling of Six Sigma by too great a number of consulting firms, many of which claim expertise in Six Sigma when they have only a rudimentary understanding of the tools and techniques involved.Potential negative effects
A FortuneFortune (magazine)
Fortune is a global business magazine published by Time Inc. Founded by Henry Luce in 1930, the publishing business, consisting of Time, Life, Fortune, and Sports Illustrated, grew to become Time Warner. In turn, AOL grew as it acquired Time Warner in 2000 when Time Warner was the world's largest...
article stated that "of 58 large companies that have announced Six Sigma programs, 91 percent have trailed the S&P 500
S&P 500
The S&P 500 is a free-float capitalization-weighted index published since 1957 of the prices of 500 large-cap common stocks actively traded in the United States. The stocks included in the S&P 500 are those of large publicly held companies that trade on either of the two largest American stock...
since". The statement was attributed to "an analysis by Charles Holland
Charles Holland
Charles Holland was an English actor, was born in Chiswick, the son of a baker.He made his first appearance on the stage in the title role of Oroonoko at Drury Lane in 1755, John Palmer, Richard Yates and Susanna Cibber being in the cast...
of consulting firm Qualpro (which espouses a competing quality-improvement process)." The summary of the article is that Six Sigma is effective at what it is intended to do, but that it is "narrowly designed to fix an existing process" and does not help in "coming up with new products or disruptive technologies." Advocates of Six Sigma have argued that many of these claims are in error or ill-informed.
Articles with critics have appeared in the November-December 2006 issue of USA Army Logistician regarding Six-Sigma: "The dangers of a single paradigmatic orientation (in this case, that of technical rationality) can blind us to values associated with double-loop learning and the learning organization, organization adaptability, workforce creativity and development, humanizing the workplace, cultural awareness, and strategy making."
A BusinessWeek
BusinessWeek
Bloomberg Businessweek, commonly and formerly known as BusinessWeek, is a weekly business magazine published by Bloomberg L.P. It is currently headquartered in New York City.- History :...
article says that James McNerney
James McNerney
W. James McNerney, Jr, is an American business executive. He is the current CEO of Boeing Company.- Education :...
's introduction of Six Sigma at 3M
3M
3M Company , formerly known as the Minnesota Mining and Manufacturing Company, is an American multinational conglomerate corporation based in Maplewood, Minnesota, United States....
had the effect of stifling creativity and reports its removal from the research function. It cites two Wharton School
Wharton School of the University of Pennsylvania
The Wharton School is the business school of the University of Pennsylvania, an Ivy League university in Philadelphia, Pennsylvania. Wharton was the world’s first collegiate business school and the first business school in the United States...
professors who say that Six Sigma leads to incremental innovation at the expense of blue skies research
Blue skies research
Blue skies research is scientific research in domains where "real-world" applications are not immediately apparent...
. This phenomenon is further explored in the book, Going Lean, which describes a related approach known as lean dynamics
Lean dynamics
Lean dynamics is a business management practice that emphasizes the same primary outcome as lean manufacturing or lean production of eliminating wasteful expenditure of resources...
and provides data to show that Ford's "6 Sigma" program did little to change its fortunes.
Lack of Proof of evidence of its success
In articles and specially on Internet sites and in text books "claims" are made about the huge successes and millions of dollars that 6-Sigma has saved. 6 sigma seems to be a "silver bullet" method. But, there seems - somehow ironic - no trustworthy evidence for this:"probably more to the Six Sigma literature than concepts, relates to the evidence for Six Sigma’s success. So far, documented case studies using the Six Sigma methods are presented as the strongest evidence for its success. However, looking at these documented cases, and apart from a few that are detailed from the experience of leading organizations like GE and Motorola, most cases are not documented in a systemic or academic manner. In fact, the majority are case studies illustrated on websites, and are, at best, sketchy. They provide no mention of any specific Six Sigma methods that were used to resolve the problems. It has been argued that by relying on the Six Sigma criteria, management is lulled into the idea that something is being done about quality, whereas any resulting improvement is accidental (Latzko 1995). Thus, when looking at the evidence put forward for Six Sigma success, mostly by consultants and people with vested interests, the question that begs to be asked is: are we making a true improvement with Six Sigma methods or just getting skilled at telling stories? Everyone seems to believe that we are making true improvements, but there is some way to go to document these empirically and clarify the causal relations."
Based on arbitrary standards
While 3.4 defects per million opportunities might work well for certain products/processes, it might not operate optimally or cost effectively for others. A pacemakerArtificial pacemaker
A pacemaker is a medical device that uses electrical impulses, delivered by electrodes contacting the heart muscles, to regulate the beating of the heart...
process might need higher standards, for example, whereas a direct mail
Direct mail
Advertising mail, also known as direct mail, junk mail, or admail, is the delivery of advertising material to recipients of postal mail. The delivery of advertising mail forms a large and growing service for many postal services, and direct-mail marketing forms a significant portion of the direct...
advertising campaign might need lower standards. The basis and justification for choosing 6 (as opposed to 5 or 7, for example) as the number of standard deviations, together with the 1.5 sigma shift is not clearly explained. In addition, the Six Sigma model assumes that the process data always conform to the normal distribution. The calculation of defect rates for situations where the normal distribution model does not apply is not properly addressed in the current Six Sigma literature. This specially counts for reliability related defects and other not time invariant problems. The IEC, ARP, EN-ISO, DIN and other (inter)national standardization organizations have not created standards for the Six Sigma process. This might be the reason that it became a dominant domain of consultants (see critics above). .
Criticism of the 1.5 sigma shift
The statistician Donald J. WheelerDonald J. Wheeler
Donald J. Wheeler is an American author, statistician and expert in quality control.Wheeler graduated from the University of Texas in 1966 and holds M.S. and Ph.D. degrees in statistics from Southern Methodist University. From 1970 to 1982 he taught in the Statistics Department at the University of...
has dismissed the 1.5 sigma shift as "goofy" because of its arbitrary nature. Its universal applicability is seen as doubtful.
The 1.5 sigma shift has also become contentious because it results in stated "sigma levels" that reflect short-term rather than long-term performance: a process that has long-term defect levels corresponding to 4.5 sigma performance is, by Six Sigma convention, described as a "six sigma process." The accepted Six Sigma scoring system thus cannot be equated to actual normal distribution probabilities for the stated number of standard deviations, and this has been a key bone of contention about how Six Sigma measures are defined. The fact that it is rarely explained that a "6 sigma" process will have long-term defect rates corresponding to 4.5 sigma performance rather than actual 6 sigma performance has led several commentators to express the opinion that Six Sigma is a confidence trick
Confidence trick
A confidence trick is an attempt to defraud a person or group by gaining their confidence. A confidence artist is an individual working alone or in concert with others who exploits characteristics of the human psyche such as dishonesty and honesty, vanity, compassion, credulity, irresponsibility,...
.
Further reading
- Hahn, G. J., Hill, W. J., Hoerl, R. W. and Zinkgraf, S. A. (1999) The Impact of Six Sigma Improvement-A Glimpse into the Future of Statistics, The American Statistician, Vol. 53, No. 3, pp. 208–215.