ENIOLA ADEOYE

(200954313)

MSc Programme in Supply Chain and Operations Management (2009/2010 session)

DMEM Department

University of Strathclyde

Glasgow

A CRITICAL LITERATURE REVIEW OF SIX SIGMA

Management of Total Quality and Continuous Improvement: 56508/56942 Coursework assessment

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Table Of ContentsAbstract........................................................................... 2Introduction..................................................................... 3Definition of Six-Sigma..................................................... 4 - 10Training and Certification................................................ 10Sounding the Operational Dimension of Six-Sigma........ 11Trends and Future Research............................................ 11 - 12Conclusion....................................................................... 12References........................................................................ 13 - 15

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A CRITICAL LITERATURE REVIEW OF SIX –SIGMA

Abstract

Purpose- This paper is an attempt to critically review academic literature on six-sigma and showcase reasons to reconsider the definition of six-sigma in literature. It addresses the issues of certification and training in six-sigma as well, and it also looks at future trends of six-sigma and tries to propose areas for further research.

Design/Methodology/Approach- Academic literatures on six-sigma were selected based on their topics, dates of publication, and sources; selection was biased towards papers that particularly did literature review on six-sigma. In all about 50 papers were selected, which was screened down to 35. The selection criteria were having contents on terms, theory and concepts in six-sigma. Sources were scholarly articles searched from Emeraldinsight, science Direct and similar databases. These papers were reviewed describing their contents in terms of trends, sources, and main emphasis on findings.

Findings- Six-sigma is a methodology that evolved out of a thorough theoretical background based on some assumptions, but the definitions given to six-sigma in the literature seems to be silent about these assumptions. There exist a search for a definition of six-sigma that takes into account all its elements with precision and no ambiguity. There exist issues around individual certification of six-sigma practitioners and certification of companies as six-sigma companies; with more issues around company certification. Six-sigma has features/characteristics that need to be researched.

Research limitations/implications- As a literature review, this paper is exploratory in nature and thus more descriptive than analytical. It is also based on secondary knowledge as other literature reviews on six-sigma were used to reach some conclusions. This implies that, there remains a need to carry out a full comprehensive literature review based on the issues raised in this paper.

Practical Implication- Six-sigma will be understood and represented with precision and consistency as a universal set having sub-set elements.

Originality/value- Among the literature available on the definition of six-sigma, this paper is the only one that is not merely concerned about the holistic or functional definition of six-sigma, but also a precise and consistent one.

Keywords- Six-sigma, Definition, Sub-set, Sustainability, Certification.

Paper Type- Critical review

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Introduction

The 21st century is an explosion of various phenomena almost at the same time which have lead to tremendous changes on how we live and do business. The customer of this age is a quality fanatic because he is well informed about what he seeks, be it a product or a service. For businesses, they are faced with ever higher standards of quality, speed and responsiveness they had to meet and surpass (Hayes et al., 2005). New products and new services are destabilizing markets and opening up opportunities. Fast products development and error-free products can be responsible for cost reduction which can offer an organization a competitive edge over the strong competitors facing him from all over the world. Six-sigma emerged as a quality management methodology to almost a dominant role at a time like this as a quality arsenal where organizations can find tools for fast product (or service) development and error-free products (or service). From inception, six-sigma has evolved through three generations according to (Montgomery and Woodall, 2008), with its final stage describing it as having additional focus (apart from variability reduction and business performance improvement which are the first and second generation of six-sigma respectively) of creating value throughout the organization and for its stakeholders.

Six-sigma originated in industry and so were early documentations and literatures on it; academics started to write on six-sigma around 1993 (Allen and Brady, 2006). Though six-sigma has made a big impact on industry, (Linderman et al., 2003) observed that the academic community lags behind in its understanding of six-sigma. Unfortunately, this view persists in academia years after. According to (Schroeder et al., 2007) a conceptual definition and identification of underlying theory are the first requirements for understanding six-sigma.

In this paper, previous work done on reviewing literature in six-sigma will be discussed; various attempts to define six-sigma will also be examined and discussed and in the end open up a proposition for why a new definition should be considered. Training and certification in six-sigma are also issues that shall be discussed as well. While most author write exclusively about six-sigma as having a project approach, nothing is said about a matching operational dimension that will sustain whatever is the output of such project. From all the literatures considered, certain features became obvious which can be described as the characteristics of six-sigma. This paper finishes by providing conclusions and future directions for research.

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The Definition of Six-Sigma

Empirical academic research did not surface in six-sigma until 2000 upwards (Nonthaleerak and Hendry, 2006) and (Prabhushankar et al., 2008) argues that since academician starting showing interest in six-sigma after the folks from industry, the development that took place in the early days of six-sigma have not been properly tracked and thus ambiguity exist in the literature with respect to the contributions that were made by the pioneers.

A ground breaking literature on six-sigma from the academic community which can be regarded as the first literature review on the subject (Nonthaleerak and Hendry, 2006) was that by (Coronado and Anthony, 2002) where literatures were reviewed to bring out the critical success factors in the implementation of any six-sigma project. As these authors’ contribution to knowledge, the project management approach and skill component of six-sigma was reinforced to form a basic component of it, and so was support from high management, cultural change and training.

Precisely 201 articles were reviewed by (Allen and Brady, 2006) describing their trends, sources and findings. The literature was synthesized with emphasis on establishing its relationship to quality management theory and topics for future research. Their paper was directed to answering such questions as: (i) what is six-sigma? (ii) Its impacts on operational performance? (iii) The roles of academics in relation to six-sigma? How they arrived at their definition of six-sigma is of interest to this paper and it will be examined in details later. Another paper that has as one of its objectives to develop holistic definition of six-sigma was (Prabhushankar et al., 2008).

A comprehensive literature review of articles on six-sigma was carried out by (Nonthaleerak and Hendry, 2006) where 200 articles were reviewed to identify key research issues that have been explored to the time of their writing, investigated research methodology employed in literature, and suggested future research areas for six-sigma.

Linderman’s definition of six-sigma in (Linderman et al., 2003) was regarded as incomplete by (Allen and Brady, 2006) because defining six-sigma as a “method” omitted philosophy and principles. They went ahead to look at what popular books and training materials have to say about six-sigma and concluded that the definition of six-sigma must contain: “Practitioners applying six-sigma can and should benefit from applying statistical methods without the aid of statistical experts.” Finally, they claim that there are enough consensuses within the six-sigma literature to offer DMAIC and DMADV as additional details about the six-sigma method in its definition. In the end, they come up with this definition:

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“Six-Sigma is a method involving Define, Measure, Analyze, Improve, and Control (DMAIC) or Define, Measure, Analyze, Design, and Verity (DMADV) as phases. We include two principles in our definition. The first emphasizes attention to the bottom line in initiating projects. The second principle emphasizes the training of non-statisticians in the vocational use of statistical tools with minimal theory.”

What is interesting about this definition to this paper is that numerous sources have been consulted and various issues have been argued before it was reached; for example, while considering the work of (Linderman et al., 2003), (Allen and Brady, 2006) realized that there was no mention of a goal of less than 3.4 defects per million opportunities for every process in that definition, though they noted that six-sigma suggests it. Emphasis was rather placed on establishing goals based on customer’s requirements which six-sigma also advocates.

Keywords of (Allen and Brady, 2006) definition:

(i) - Attention to bottom line(ii) -Projects(iii) -Statistics(iv) -Training

The DMAIC and DMADV are also vital but in this case are sources of confusion, as certain issues were not clarified by their arguments. They reckoned multiple techniques are often used in six-sigma, therefore the definition of six-sigma as a “method” complicates reference to the techniques used in its application. They in the end proposed that the techniques should be referred to as sub-method. Is DMAIC used for six-sigma? And DMADV for Design for six-sigma? Or whenever we say “six-sigma” we expect that we should be understood out of context as regarding if we are referring to six-sigma that uses DMAIC (in which some have termed “continuous improvement” subset of six- sigma)? Or the one that uses DMADV (also known as design for six-sigma)? This paper will discuss these issues later.

Another attempt was made by (Prabhushankar et al., 2008) to define six-sigma in a holistic way, they checked the literature and discovered three categories of definitions for six-sigma:

(i) -That is statistics-based definitions(ii) -Management oriented-based definitions (iii) -Both statistic-based and management-oriented definitions

They ended up with this definition which they described as holistic definition of six-sigma:

“Six Sigma can be defined as a highly disciplined, organized, systematic, proactive, powerful and multifaceted problem-solving or continuous and/or breakthrough business/process improvement strategy that seeks to find and eliminate the sources of error or the causes of

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customer-defined mistakes or defects, drive out wastes in business processes, and reduce variation, thereby improving the efficiency and effectiveness of organizational operations, and strives to reach a level of 3.4 DPMO using extremely rigorous data gathering and statistical analysis, thereby meeting or even exceeding customers’ needs and expectations with a focus on financially measurable bottom-line results.”

Key phrases derived from various sources used by (Prabhushankar et al., 2008) at arriving at the definition given above are listed below:

(i) -Highly disciplined (ii) -Organized(iii) -Powerful, multifaceted, systematic, proactive(iv) -Continuous or breakthrough process improvement program or approach(v) -Business/Process improvement strategy(vi) -Process improvement philosophy (vii) -Eliminate sources of error or customer-defined mistakes/defects(viii) -Drive out/Minimize wastes in business process(ix) -Reduce variation (x) -Improve efficiency and effectiveness(xi) -Goal or 3.4 DPMO (xii) -Rigorous data gathering and statistical analysis(xiii) -Customer focus: meeting/exceeding customers’ needs or expectations(xiv) -Focus on financial bottom-line results

The importance of (Prabhushankar et al., 2008) review to this work is that it had looked at virtually all the definitions available on six-sigma to arrive at its own definition. It is not likely that any material picked up today be it a popular book on six-sigma, academic article or magazine on six-sigma that gives a definition of six-sigma will not contain at least one of the key words listed above.

(Prabhushankar et al., 2008) had done the job to a point. The issue now is, if a new kind of knowledge has a theoretical base, the assumptions used in formulating the theory should reflect in its definition and it should serve as the gate for anyone coming in to use such knowledge. “Rigorous academic research of six-sigma requires the formulation and identification of useful theories related to the phenomenon” (Linderman et al., 2003). The authors argue that without knowledge, improvement only occurs through incidental or implicit learning, meaning, an event that occurs by chance and is rarely understood. Many practitioners of six-sigma are considered ignorant of the term DPMO though they use it (Maleyeff and Krayenvenger, 2004). They pointed out that as a result of this and other misconceptions and the thriving business of six-sigma consulting (Bhote, 2002) suggested that two types of six-

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sigma exist: “the statistical six-sigma” and “the hyped six-sigma.” Six-sigma initial concepts were among issues considered by (Nonthaleerak and Hendry, 2006).

From all that has been discussed, it is obvious that six-sigma is a subject that is still in it formative years, only that it was too effective not to be noticed. It is clear from the definitions given to it that it has both quantitative (statistical) and qualitative (business/management) components like economics. Economics was initially only a descriptive subject and when the quantitative part was evolving, it was modelled after physic which was considered an ideal physical science for that purpose (Green, 1995). In the light of this, every physical law of physics reflects the assumption(s) behind it and the benefit of that is that whenever such law is used it can be used in an adaptable fashion. For example, Hooke’s law of elasticity: The elasticity in a spring is directly proportional to the load causing it, provided the elastic limit is not exceeded. Examples of how assumptions made behind a theory might reflect in the definition of a physical law, “provided air resistance is zero, or temperature is constant” etc. These were assumptions made when such laws were formulated and it reflected in their definitions. Various assumptions were made in the formulation of six-sigma, though they have raised a lot of controversies in the literature (Montgomery and Woodall, 2008), which need to be clarified (thus, still remains an area to research) in such a way that scholars will reach a consensus about and not argue and the outcome will be used to form a theoretical base in defining six-sigma without leaving out such contribution as (Prabhushankar et al., 2008) who gave a holistic definition of Six-sigma.

The assumptions made at the beginning of six-sigma have raised a lot of controversies in academia; these were the arguments of (Montgomery and Woodall, 2008):

“Under the Six Sigma concept, an assumption was made that when the process reached the Six Sigma quality level, the process mean was still subject to disturbances that could cause it to shift by as much as 1.5 standard deviations off target. Under this scenario, a Six Sigma process would produce up to 3.4 parts per million (ppm) non-conforming to specifications. The drifting mean aspect of the Six Sigma metric has been a source of controversy. Some have argued that there is an inconsistency in that we can only make predictions about process performance when the process is stable, i.e. the mean and standard deviation are constant over time. If the mean is drifting, a prediction of up to 3.4 ppm non-conforming to specifications may not be very reliable, because the mean might shift by more than the “allowed” 1.5 standard deviations.”

They also reported in their work that advocate of Deming’s philosophy have rejected six-sigma in some cases claiming it violated some of Deming’s 14 points. However they argued in the end that the 3.44 ppm metric is increasingly recognized as primarily a distraction; that the focus on variability reduction and elimination of waste and defects is what is key about six-sigma. This sounded more like the answer someone from industry will give to an issue like this and not someone in academia. Result should definitely satisfy someone in industry, since theoretical issues are secondary to practitioners (Stephens, 2001), but an academic will seek clarification of

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all concepts and the controversies associated with them. The literature lacks any interrogation of the theoretical basis of Six Sigma (Shahabuddin, 2008).

(Maleyeff and Krayenvenger, 2004) were very clever in their approach to addressing all the assumptions behind six-sigma and the controversies associated with them. They explained everything through and their word is worth seeing by anyone who craves an understanding on these issues. In brief, they explained that some practitioners may be aware that when part specifications are set six-sigma units from nominal specification, only 3.4 defects per million (DPMO) will occur (only when the process mean is shifted 1.5 sigma-units away from nominal and only when the process is normally distributed). A number of misconceptions exist regarding six-sigma they reckoned. For example, the goal of 3.4 DPMO is placed on each critical characteristic and not on final product, thus the quality level of a product will vary depending on the number of critical characteristics the product contained. The establishment of 3.4 DPMO goal at Motorola Corporation in the 1980s based on existing product designs and process characteristics. Three key factors recognized in product development were the product’s complexity [represented by a number of opportunities for defects (OFD)] contained in a product, the goal quality level of the final product and, the expected mean shift run-to-run which was assumed to be 1.5 sigma units.

Figures I a and I b below taken from (Montgomery and Woodall, 2008) illustrates the 1.5 sigma units shift allowance assumed about six-sigma. Another issue at this point is that the six-sigma curve though normally distributed is a varied version of the statistical normal curve. The implication of this is that six-sigma on the normal curve points to a position of 2 defects in 2 billion opportunities (also known as DPMO short-term in literature), while our 3.4 DPMO is only the six-sigma position on our six-sigma curve, but 4.5 sigma units on the normal curve (also known as DPMO long-term with 1.5 sigma units shift in literature).

These issues are still taking the attention of scholars and practitioners involved with six-sigma. For anyone interested in these issues, (Shahabuddin, 2008) “Six-sigma: Issues and problems” is worth seeing.

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Figures Ia and Ib taken from (Montgomery and Woodall, 2008)

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Another ambiguity about six-sigma’s definition is about its sub elements. Authors do use the term six-sigma and expect to be understood out of context especially when they have to talk about six-sigma and DFSS. (Coronado and Anthony, 2002) had this issue when literatures were reviewed to bring out the critical success factors of a Six-sigma project. This issue in the paper: Going from six-sigma to design for six-sigma (Coronado and Anthony, 2003); at a point they had to break the term “six-sigma” to its continuous improvement component and its DFSS to components clarify their point. Another issue that this points to is that: is the continuous improvement component actually six-sigma? Since it is reported in the literature that unless a DFSS is undertaken, the best that can result from a “conventional” six-sigma process is between 4.8 sigma units to 5.0 sigma units and the only way to guarantee six-sigma quality level is DFSS (Coronado and Anthony, 2002), (Coronado and Anthony, 2003). So is “six-sigma” six-sigma? Or something less when looking at it from the continuous improvement perspective? DFSS was described as taking six-sigma upstream by (Hasenkamp and Olme, 2008).

Is DFSS a continuation of six-sigma or its sub-set? The point of contention here is how we define six-sigma that will explain clearly in practical terms the relationship that exists between its CI component and DFSS component.

Training and Certification

The issue here is that there are a lot of programs with certifications ranging from Champions (sponsors of six-sigma projects) to Master Black Belt through to Yellow Belts. These certifications are for individuals and are not standardized; the content of what was taught and learnt depends on the organization rendering it. Also companies that are called six-sigma companies are called that by their own saying (Davenport, 2005). There is no certifying body like the case of ISO 9000 that has established an assessable quality standard across industries. The implication of this is that during the capability investigation in a six-sigma project, a company will easily see other companies that might be operating at a higher sigma level higher than them and with that have an option of outsourcing.

Six-sigma has attracted interest from different disciplines, this is accounted for based on the fact that it is a project that is team based, thus training must be framed in such a way that it takes care of everyone’s background. (Montgomery and Woodall, 2008) have advocated more training in business, management and even manufacturing for statisticians; because in their view, six-sigma has impacted the roles of statisticians of the future. On the other hand, statistical training has been recommended from those involved with six-sigma project that have no or weak statistical background (Anthony et al, 2005), (Allen and Brandy, 2006). This is often the case of an emerging knowledge that has both qualitative and quantitative components. To address issues such as these, the University of Arizona has established their own university based six-sigma programme and some other universities are following suit.

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Sounding the Operational Dimension of Six-Sigma

Six-sigma is often referred to as a project and thus has a starting date and a closing date. The literature is often silent about this. The discipline of six-sigma must possess within its package the knowledge of what to do when the six-sigma project is completed in operational terms. This is the only way that sustainability of the benefits of the project can be enhanced. At the end of every project, a product is delivered, how is this product launched in to an organization’s operating system? Certainly, it is being done somehow for us to report the success of six-sigma in various industries, but it has not been given attention in the literature. So much is said about the project, but nothing about the product and how to manage it since it is responsible for the result or changes that we see after the project.

Trends and Future Research

There is a concept termed “six-sigma enhancement” by (Nonthaleerak and Hendry, 2006) in their work, one point of interest to this paper among the points raised was widening the applicability of six-sigma in business with the example of lean six-sigma. This became the trend in the literature about six-sigma at some point, the widening of its applicability, either by combining/ integrating it with other methodologies or by applying it in an entirely new area. (Kwak and Anbari, 2006), recognized the efforts of researchers and practitioners to integrate six-sigma with other existing innovative management practices.

Some of such papers are these in Table I below:

Author(s) Topic1 Maleyeff, (2007) Improving Service Delivery in Government with Lean Six Sigma.2 Kent Snyder, (2004) Lean Six sigma in the Public Sector.3 Loon Ching Tang et al,

(2007)Fortification of Six Sigma: Expanding the DMAIC Toolset.

4 Yuriarto and Elhag, (2008)

Enhancing Six Sigma with System Dynamics.

5 Nonthaleerak and Hendry, (2008)

Exploring the Six Sigma Phenomenon using Multiple case Study Evidence.

6 Chassin, (1998) Is Health care ready for Six Sigma Quality?7 Jiantong and Wenchi,

(2007)Study of implementing Six Sigma in Banking.

8 McAdam et al, (2009) Customer – Oriented Six Sigma in Call centre Performance Measurement.

9 Henley and Dobie, (2005)

Assessing readiness for Six-sigma in a Service setting

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Jiju Anthony, (2004) Six-sigma in UK service organizations

1 Kumar, et al, (2007) Winning Customer loyalty in an Automotive company through

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1 Six Sigma: a case study. 13

Revere and black, (2003)Hammer and Goding, (2001)

Integrating and Comparing Principles and Characteristics of Six Sigma with Total Quality Management.

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Wyper and Harrison, (2000)

Integrating and Comparing Principles and Characteristics of Six Sigma with Human Resources Functions.

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Anthony, et al, (2003) Integrating and Comparing Principles and Characteristics of Six Sigma with Lean Production.

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Catherwood, (2002) Integrating and Comparing Principles and Characteristics of Six Sigma with ISO 9000.

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Dalgleish, (2003) Integrating and Comparing Principles and Characteristics of Six Sigma with ISO 9001.

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Murugappan and Keeni, (2003)

Integrating and Comparing Principles and Characteristics of Six Sigma with Capability Maturity Model.

Table I: showing different topics that depicts the applicability of Six Sigma.

The point now is that there is need to research the features of six-sigma in other to determine and decipher it compatibility factor as it is emerging as the gold mine of quality tools and techniques of the 21st century. Another question that will be solved by that is this: Is six-sigma analogous to a computer hardware that lots of programs can run on it or is it software that can run on a lot of hardwares? The understanding of this will help both scholars and practitioner in adapting six-sigma to new areas and may be in the future, we shall be able to adapt it to tackle a problem that is not normally distributed.

Conclusion

This paper has proposed that a definition of six-sigma should be derived with consensus among scholars and it must expose the theoretical base of six-sigma and all the assumptions made. It must explain clearly the relationship between the CI subset of six-sigma and the DFSS subset and how they fit in to the universal set of six-sigma without leaving out everything that is said about six-sigma so far that is correct. Certification of companies as a six-sigma company should be examined and six-sigma training should be given a baseline.The compatibility factor of six-sigma should be researched.

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