Six Sigma quality: a structuredreview and implications for future

researchMohamed Gamal Aboelmaged

Management Department, College of Business Administration,Ajman University of Science and Technology, Ajman, United Arab Emirates

Abstract

Purpose This paper aims to clarify emerging aspects and trends of Six Sigma literature over 17years, from 1992 to 2008.

Design/methodology/approach The literature on Six Sigma from 417 referred journal articles inbusiness and management disciplines, information systems and computer science, engineering,healthcare, etc. were systematically analyzed based on a scheme that consists of four distinctdimensions: publication year and journal, major themes, research type, and application sector (i.e.manufacturing vs service).

Findings A number of key findings emerged: Six Sigma research is growing rapidly, coveringvarious disciplines and domains with a great focus on Six Sigma tools and techniques; empiricalresearch is dominant with more emphasis on case study approach; and the growing gap betweenmanufacturing- and service-focused articles implies the return of Six Sigma to manufacturing as itsinitial base. Although a large volume of literature is available on Six Sigma, the topic is still underdevelopment and offers potential opportunities for further research and applications.

Originality/value The paper provides both academics and practitioners with a useful frameworkfor pursuing rigorous Six Sigma research through explaining the chronological growth of Six Sigma,challenging themes of Six Sigma research, dominating research types and application areas in SixSigma, and the major sources of Six Sigma information.

Keywords Six Sigma, Total quality management, Lean production, Supply chain management

Paper type Literature review

IntroductionSix Sigma has evolved from scientific management and continuous improvementtheories by combining the finest elements of many former quality initiatives.Originally, Motorola was the first to launch a Six Sigma program in the 1980s. In 1988,Motorola was the first company awarded the Baldrige Award, which led otherorganizations to show an increased interest in adopting and modifying Six Sigmamethodology. Companies such as Allied Signal, IBM, and General Electric adopted SixSigma as a corporate requirement for strategic and tactical operations to producehigh-level results, improve work processes, expand employees skills and change theculture. Now, Six Sigma is well established in almost every industry and manyorganizations worldwide have modified Six Sigma methodology and tools to fit theirown operations.

For the term Six Sigma there appears to be little consensus on its definition.Proposing an emergent definition of Six Sigma based on a grounded theory approach,Schroeder et al. (2008) concluded that Six Sigma offers a new structure that promotes

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Received March 2009Revised September 2009Accepted September 2009

International Journal of Quality &Reliability ManagementVol. 27 No. 3, 2010pp. 268-317q Emerald Group Publishing Limited0265-671XDOI 10.1108/02656711011023294

both control and exploration in improvement efforts. They asserted that academicsneed to develop a deeper and richer knowledge of Six Sigma so that they do not overhype or quickly dismiss it. Table I shows examples of Six Sigma definitions that reflectdifferent perspectives. From a statistical perspective, Six Sigma is a metric of processmeasurement symbolized by the Greek letter s that represents the amount of variationwith a normal data distribution. Fundamentally, Six Sigma quality level relates to 3.4defects per million opportunities (DPMO). The focus of Six Sigma is not on countingthe defects in processes, but the number of opportunities within a process that couldresult in defects so that causes of quality problems can be eliminated before they aretransformed into defects (Antony, 2006). From a business perspective, Six Sigma couldbe described as a process that allows companies to drastically focus on continuous andbreakthrough improvements in everyday business activities to increase customersatisfaction (Andersson et al., 2006).

In this paper, we classify the literature on Six Sigma research and present acomprehensive review of these studies. The review covers 417 journal articles

Andersson et al. (2006) Improvement program for reducing variation, whichfocuses on continuous and breakthroughimprovements

Antony (2002) A business performance improvement strategy thataims to reduce the number of mistakes/defects toas low as 3.4 occasions per million opportunities

Banuelas and Antony (2002) A philosophy that employs a well-structuredcontinuous improvement methodology to reduceprocess variability and drive out waste within thebusiness processes using statistical tools andtechniques

Behara et al. (1995) The rating that signifies best in class, with only 3.4defects per million units or operations

Bendell (2006) A strategic, company-wide, approach . . . focusing onvariation reduction, projects have the potential ofsimultaneously reducing cost and increasingcustomer satisfaction

Black and Revere (2006) A quality movement, a methodology, and ameasurement. As a quality movement, Six Sigma is amajor player in both manufacturing and serviceindustries throughout the world. As a methodology,it is used to evaluate the capability of a process toperform defect-free, where a defect is defined asanything that results in customer dissatisfaction

Chakrabarty and Tan (2007) A quality improvement program with a goal ofreducing the number of defects to as low as 3.4 partsper million opportunities or 0.0003 per cent

Kwak and Anbari (2006) A business strategy used to improve businessprofitability, to improve the effectiveness andefficiency of all operations to meet or exceedcustomer needs and expectations

Table I.Examples of Six Sigma

definitions

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published between 1992 and 2008. The paper is divided into four remaining sections.First, the research methodology used in the study is described. This is followed by theclassification framework in the second section. Third, Six Sigma articles are analyzedand the classification results are reported. Fourth, conclusions are presented and theimplications of the study are discussed.

Research methodologyThe research targeted peer-reviewed journal papers having more than two pages, asacademics and practitioners alike most often use journals to obtain information anddisseminate the highest level of research findings, both in width and breadth researchfindings. Therefore, editorials, news reports, book reviews, viewpoints, conferencepapers, masters and doctoral dissertations, textbooks, and unpublished workingpapers were excluded. The survey focused only on papers with Six Sigma as a part oftheir titles. The exceptions are those articles that are explicitly dealing with SixSigma but for some reasons the authors decided to use one of Six Sigmamethodologies, DMAIC or DFSS, in the title. Finally, to avoid never ending revisionof the article, the end of 2008 was selected as the cut-off date. These criteria shouldallow a quality and comprehensive set of papers on Six Sigma by different fields. Thecompiling effort has been carried out over 19 months through extensive databasesearch, internet search, reference checking, etc. However, it is possible that there existan article that is not surveyed in this paper.

Considering the nature of the research on Six Sigma, it would be difficult to groupthe literature under any specific disciplines. As a result, various online journaldatabases shown were selected and searched to provide a comprehensive bibliographyon Six Sigma literature. The literature contributions were primarily of articles fromresearch databases including Emerald, Science Direct (Elsevier), ProQuest Global,Interscience, Inderscience, ASQ, Springer and IEEE-Xplore. These databases provideonline delivery systems with full text access to thousands of high quality articles andjournals that cover a wide range of social and applied science titles including businessand management disciplines, engineering, healthcare and computer science. Thesearch yielded 417 Six Sigma articles from 147 journals. Each article was carefullyreviewed and then the data was organized to produce a classification from severalperspectives. Although this research is not exhaustive, it serves as a comprehensivebase for an understanding of Six Sigma research.

Classification frameworkThe classification framework was based on the literature review, the nature of SixSigma research, and the work of Nonthaleerak and Hendry (2006) and Brady and Allen(2006). The articles were reviewed, analyzed and classified based on four dimensions asfollows:

(1) Publication year and journal.

(2) Major theme and subject.

(3) Research type.

(4) Application sector: manufacturing vs service.

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This framework will provide guidelines for pursuing rigorous Six Sigma research byexplaining the chronological growth of Six Sigma, challenging themes of Six Sigmaresearch, dominating research types and application areas in Six Sigma and the majorsources of Six Sigma information.

Results and analysis of the classificationsDistribution by year of publicationFigure 1 shows the distribution of 417 Six Sigma articles published over the periodfrom 1992 to 2008. There appears to be limited research outputs before 2000. Theblooming years for Six Sigma research were between 2000 and 2006 since the numberof journal articles has increased significantly over this period, and started to decline in2007. However, the escalation in number of Six Sigma articles in 2008 is noteworthy.

Distribution of articles by journalThere were a total of 147 different journals from various business, engineering, statistics,information systems/technology and healthcare disciplines that published Six Sigmaarticles. Figure 2 demonstrates that the vast number of articles (122 articles, 53 percent)is published in 14 journals, while 196 articles (47 percent) were published in 133 journals,among them 91 journals published one article only and 42 journals published 2 to 4articles each. Among the leading journals, International Journal of Six Sigma andCompetitive Advantage had by far the largest number of articles per journal (72 articles,17.3 percent). Since 2004, the journal is devoted to advancing the understanding andpractice of Six Sigma research. To reflect the close relationship between total qualitymanagement and Six Sigma research, total quality management journals had the secondlargest percentages of Six Sigma articles. This includes Total Quality Management andBusiness Excellence and The TQM Journal (previously, The TQMMagazine which sharethe second position (27 articles, 6.5 percent each). Besides, the engineering perspective to

Figure 1.Distribution of Six Sigma

articles by year(1992-2008)

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quality deployment is noticeable in Six Sigma articles since the third and fourth largestpercentages of Six Sigma articles are in Quality Engineering (23 articles, 5.5 percent) andQuality and Reliability Engineering International (18 articles, 4.3 percent). InternationalJournal of Product Development (eight articles, 1.9 percent) had the fifth position.International Journal of Quality & Reliability Management and International Journal ofProduction Research share the sixth position (seven articles, 1.67 percent each). Theseventh position is shared by The Quality Management Journal and The Journal of

Figure 2.Distribution of Six Sigmaarticles by journals

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Validation Technology (six articles, 1.43 each). Four journals including MeasuringBusiness Excellence, Journal of Organizational Excellence, Journal of ManufacturingTechnology Management, and Journal of Healthcare Management share the eighthlargest percentages of Six Sigma articles (five articles, 1.2 percent each). Surprisingly,these 14 journals represent the main disciplines that construct Six Sigma research;business, engineering, and healthcare. A comprehensive list of all contributing journalsis illustrated in the Appendix.

Distribution of articles by themesTable II provides a comprehensive list containing the themes and their classifiedreferences for each theme. It is unavoidable to have an article that is relevant to morethan one theme, so listing an article under more than one theme was allowed. Forexample, an article may address critical success factors for Six Sigma implementationbut provide information on Six Sigma tools and techniques. In such a case, a moreweighted theme is chosen to classify the article according to the authors judgment. Atotal of 13 themes were identified in Six Sigma articles. The most heavily publishedtheme is in Six Sigma tools and techniques (169 articles). The two major Six Sigmamethodologies, DMAIC and DFSS, made up the second largest proportion within SixSigma themes (87 articles). DAMIC (54 articles) and DFSS, design for Six Sigma (33articles). The conventional relationship between Six Sigma and other qualityapproaches, TQM and continuous improvement in particular, had the third largestnumber of articles (48 articles), while the human structure of Six Sigma in terms of theBelt system had the fourth position (37 articles) (Figure 3).

This is followed by the relationship between Six Sigma and lean production in thefifth position (34 articles). Success factors for Six Sigma implementation is the sixthlargest proportion within Six Sigma themes (33 articles). Evaluating Six Sigma interms of challenges and benefits is in the seventh and eighth positions with 31 and 29articles continuously. Selection of Six Sigma project is in the ninth position (16 articles).Themes that link Six Sigma with management disciplines are also present. Thisinvolves organizational change in the tenth position (14 articles), supply chain in the11th position (13 articles) and organizational learning in the 13th position (sevenarticles). Surprisingly, there are relatively fewer articles on Six Sigma education in the12th position (11 articles). An elaboration of the cited themes is presented in thefollowing subsections.

Six Sigma tools and techniques. The great deal of Six Sigma literature has focused onSix Sigma tools and techniques. They can be described as practical methods and skillsemployed by Six Sigma project teams to tackle quality related problems for fosteringperformance improvement. While Six Sigma tool has a specific role and is often narrowin focus, Six Sigma technique has a wider application and requires specific skills,creativity and training (Antony, 2006). Examples of Six Sigma tools include Paretoanalysis, root cause analysis, process mapping or process flow chart, Gantt chart,affinity diagrams, run charts, histograms, quality function deployment (QFD), Kanomodel, brainstorming, etc. Examples of Six Sigma techniques include statistical processcontrol (SPC), process capability analysis, suppliers-input-process-output-customer(SIPOC), SERVQUAL, benchmarking, etc. Moreover, a Six Sigma technique can utilizevarious tools. For example, statistical process control (SPC) is a technique that utilizesvarious tools such as control charts, histograms, root cause analysis, etc.

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Theme References Total

Tools andtechniques

Adams et al. (2004); Al-Aomar (2006); Al-Aomar and Youssef (2006);Antony (2006); Antony (2007a); Antony and Fergusson (2004); Antony et al.(2001); Antony et al. (2005); Antony et al. (2007a); Antony et al. (2007c);Banuelas and Antony (2003); Banuelas et al. (2005); Basu (2004); Beard(2008); Bellows (2004); Benedetto (2003); Bhatnagar and Pandey (2005);Biedry (2001); Biehl (2004); Bigio et al. (2004); Box and Luceno (2000);Brewer and Eighme (2005); Bunce et al. (2008); Card (2000); Carrigan andKujawa (2006); Caulcutt (2001); Chan et al. (2005); Chang and Su (2007);Chang and Wang (2008); Chatterjee (2003); Chen et al. (2007); Chen et al.(2005a, b); Cheng (2007b, c); Cheng et al. (2008); Cook et al. (2005); Cupryket al. (2007); Das and Hughes (2006); De Koning and De Mast (2006); DeVore (2008); Doble (2005); Does et al. (2002); Drenckpohl et al. (2007);Echempati and White (2000); Ehie and Sheu (2005); Elberfeld et al. (2007);Eldridge et al. (2006); Erlandson (2006); Fairbanks (2007); Flott (2000);Frank (2003); Frankel et al. (2005); Fuller (2000b); Gack and Robison (2003);Glower (2006); Goh (2002b); Goh and Xie (2003); Goh and Xie (2004); Gohet al. (2003); Graves (2002); Hahn (2005); Hahn et al. (1999); Han and Lee(2002); Hare (2005); Harjac et al. (2008); Harrington and Trusko (2005);Henderson and Evans (2000); Hendricks and Kelbaugh (1998); Holtz andCampbell (2004); Hong and Goh (2003); Hsu et al. (2005, 2008); Huq (2006);Hutchins (2000); Hwang (2006); Ingram (2000a, b, c); Isaacson (2008);Johnston et al. (2008); Johnstone et al. (2003); Juras et al. (2007); Kanji (2008);Kapur and Feng (2005); Kaushik et al. (2008); Knowles et al. (2004); Krishnaand Dangayach (2007); Krishna et al. (2008); Kumi and Morrow (2006);Ladani et al. (2006); Lee-Mortimer (2006, 2007); Li et al. (2006); Lin et al.(2008); Lipscomb and Lewis (2004); Little (2003); Lloyd (2006); Lucier andSeshadri (2001); McAdam and Lafferty (2004); Mahanti (2005); Mahantiand Antony (2005, 2006); Mahesh et al. (2006); Maleyeff and Kaminsky(2002); Maleyeff and Krayenvenger (2004); Malhan and Rao (2005); Malligaand Srinivasan (2007); Manikandan et al. (2008); Manual (2006); Markarian(2004a, b); Miles (2006); Montgomery and Woodall (2008); Moorman (2005);Morgan and Cooper (2004); Mukhopadhyay and Ray (2006); Murugappanand Keeni (2003); Neagu and Hoerl (2005); Ng et al. (2005); Nonthaleerakand Hendry (2008); ONeill (2005); Pan and Cheng (2008); Pandey (2007);Patterson et al. (2005); Perng et al. (2008); Perry and Barker (2006); Phengand Hui (2004); Raisinghani et al. (2005); Rajagopalan et al. (2004);Ravichandran (2006, 2007, 2008); Revere et al. (2004); Sadagopan et al.(2005); Sahoo et al. (2008); Sarkar (2007a); Schon (2006); Schroeder et al.(2008); Sehwail and De Yong (2003); Sekhar and Mahanti (2006); Setijono(2008); Smith (1993); Snee (2004); Stewart and Spencer (2006); Su et al.(2005); Sudhahar et al. (2008); Taner et al. (2007); Tannock et al. (2007);Thakkar et al. (2006); Thiele et al. (2008); Thomas and Barton (2006);Thomas and Lewis (2007); Thompson et al. (2008); Ung et al. (2007); VanDen Heuvel et al. (2005); Van Iwaarden et al. (2008); Vaughan (1998); Voteand Huston (2005); Woodall (2001); Woodard (2005, 2006); Wright andBasu (2008); Xue-Liang et al. (2007); Yang (2004); Zaroukian and Sierra(2006); Zhan (2008)

169

(continued)

Table II.Classification of SixSigma articles by themes

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Theme References Total

Methodology 87DAMIC Antony (2006); Antony et al. (2007c); Bandyopadhyay and Jenicke (2007);

Bandyopadhyay and Lichtman (2007); Banuelas et al. (2005); Brewer andEighme (2005); Chen et al. (2005, 2008); Cronemyr (2007); De Koning andDe Mast (2005); Dedhia (2005); Dreachslin and Lee (2007); Drenckpohl et al.(2007); Edgeman and Dugan (2008); Edgeman et al. (2005); Friday-Stroudand Sutterfield (2007); Hamza (2008); Henderson and Evans (2000); Ho andChuang (2006); Holtz and Campbell (2004); Hu et al. (2005); Jenicke et al.(2008); Kaushik and Khanduja (2008); Kuei and Madu (2003); Kumar et al.(2008a, b); Kumi and Morrow (2006); Lee-Mortimer (2007); Li and Al-Refaie(2008); Li et al. (2008); Lipscomb and Lewis (2004); Lloyd (2006); McCartyand Fisher (2007); Mahanti and Antony (2005, 2006); Mahesh et al. (2006);Man (2002); Miles (2006); Neri et al. (2008); Sanders and Hild (2000c);Schroeder et al. (2008); Sehwail and De Yong (2003); Szeto and Tsang (2005);Taghaboni-Dutta and Moreland (2004); Taner et al. (2007); Tang et al. (2007);Thawani (2004); Thomas and Barton (2006); Thomas and Lewis (2007);Tong et al. (2004); Vote and Huston (2005); Wyper and Harrison (2000); Yeh(2007); Yeh et al. (2007) 54

DFSS Amer et al. (2008); Anand et al. (2007); Antony (2002); Banuelas and Antony(2003, 2004); Bayle et al. (2001); Chang and Su (2007); Chung et al. (2008);De Feo and Bar-El (2002); Erlandson (2006); Ferryanto (2007); Gerhorst et al.(2006); Goh (2001); Gremyr (2005); Hasenkamp and Olme (2008); Hu andAntony (2007); Hu and Pieprzak (2005); Johnson et al. (2006a); Kalamdaniand Khalaf (2006); Khalaf and Yang (2006); Kovach (2007); Kovach and Cho(2006); Liu et al. (2008); Mekki (2006); Rajagopal and Castillo (2007); Savage(2007); Savage and Son (2008); Shahin (2008); Sokovic et al. (2005); Thomasand Singh (2006); Yang (2005) 33

Quality approaches Aggogeri and Gentili (2008); Al-Mishari and Suliman (2008); Anderssonet al. (2006); Antony (2002); Black and McGlashan (2006); Camgoz-Akdag(2007); Cheng (2007c); Cheng (2008); Craven et al. (2006); Dahlgaard andDahlgaard-Park (2006); Davison and Al-Shaghana (2007); Delsanter(1992); Ehie and Sheu (2005); Ferng and Price (2005); Foster (2007);Freiesleben (2007); Furterer and Elshennawy (2005); Goeke and Offodile(2005); Green (2006b); Hagemeyer et al. (2006); Haikonen et al. (2004);Hild et al. (2000); Hoerl (1998); Hong and Goh (2004); Jeffery (2005);Klefsjo et al. (2006); Klefsjo et al. (2001); Knowles et al. (2004); Krishnaet al. (2008); Lupan et al. (2005); Pfeifer et al. (2004); Revere and Black(2003); Ribardo and Allen (2003); Ricondo and Viles (2005); Sadagopanet al. (2005); Sarkar (2007b); Savolainen and Haikonen (2007); Schroederet al. (2008); Stewart and Spencer (2006); Thirunavukkarasu et al. (2008);Thomas et al. (2008a); Walters (2005); Wessel and Burcher (2004); Yang(2004); Yang and Yeh (2007); Yeung, S. (2007); Zhang and Xu (2008);Zu et al. (2008) 48

(continued) Table II.

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Theme References Total

Belt system Andersson et al. (2006); Antony (2004b); Antony et al. (2001, 2005, 2007b, c);Banuelas et al. (2006); Bendell (2006); Black and McGlashan (2006); Blackand Revere (2006); Buch and Tolentino (2006a, b); Gowen (2005); Green(2006a); Green et al. (2006); Hagemeyer et al. (2006); Haikonen et al. (2004);Henderson and Evans (2000); Ho et al. (2008); Hoerl et al. (2001); Ingle andRoe (2001); Johnson et al. (2006b, c); Klefsjo et al. (2001); Kwak and Anbari(2006); Lee-Mortimer (2006); Linderman et al. (2003, 2006); Mitra (2004);Motwani et al. (2004); Pandey (2007); Pfeifer et al. (2004); Rasis et al.(2002a, b); Sadagopan et al. (2005); Savolainen and Haikonen (2007);Schroeder et al. (2008) 37

Lean production Al-Aomar (2006); Andersson et al. (2006); Bendell (2006); Bonilla et al. (2008);Brett and Queen (2005); Byrne et al. (2007); Chang and Su (2007); Cupryket al. (2007); Dahlgaard and Dahlgaard-Park (2006); De Koning et al. (2006,2008a, b); Fairbanks (2007); Ferng and Price (2005); Furterer andElshennawy (2005); Gibbons (2006); Hu et al. (2008); Jin et al. (2008); Khalafand Yang (2006); Kumar et al. (2006); Marti (2005); Mazzola et al. (2007);Morgan and Cooper (2004); Naslund (2008); Pickrell et al. (2005); Pojasek(2003); Proudlove et al. (2008); Ricondo and Viles (2005); Shah et al. (2008);Shahin and Alinavaz (2008); Sharma (2003); Su et al. (2006); Thomas et al.(2008b); Van Den Heuvel et al. (2006) 34

Success factors Antony (2004a, 2006, 2008a); Antony and Banuelas (2002); Antony andFergusson (2004); Antony et al. (2005, 2007a, 2008); Buch and Tolentino(2006a, b); Byrne (2003); Chakrabarty and Tan (2007); Cheng (2007a, 2008);Chung et al. (2008); Coronado and Antony (2002); Feng and Manuel (2008);Frings and Grant (2005); Gowen (2005); Hilton et al. (2008); Ho et al. (2008);Jenicke et al. (2008); Kumar (2007); Laosirihongthong et al. (2006); Lindermanet al. (2003, 2006); McAdam and Evans (2004b); Knowles et al. (2005);Sanders and Hild (2000a); Shanmugam (2007); Szeto and Tsang (2005);Wessel and Burcher (2004); Yang et al. (2008) 33

Challenges Antony (2004b, 2006, 2007b, 2008a, b); Antony et al. (2001, 2008); Cheng(2007a); Feld and Stone (2002); Gijo and Rao (2005); Goh and Xie (2004); Gohet al. (2006); Hammer (2002); Ho et al. (2006); Hoerl (1998); Kumar (2007);Kumar et al. (2008); Kwak and Anbari (2006); Lee and Choi (2006); Liu et al.(2008); McAdam and Evans (2004a, b); McAdam and Lafferty (2004);McAdam et al. (2005); McClusky (2006); Nonthaleerak and Hendry (2006);Sanders and Hild (2000b); Senapati (2004); Shahabuddin (2008); Van DenHeuvel et al. (2004); Yeung, S. (2007) 31

Benefits Agarwal and Bajaj (2008); Aggogeri and Gentili (2008); Antony (2004b,2006); Antony et al. (2001, 2005, 2007c); Behara et al. (1995); Carnell andLambert (2000); Chen et al. (2005); Das et al. (2006); De Mast (2006); Desai(2006, 2008); Douglas and Erwin (2000); Feld and Stone (2002); Freiesleben(2006); Ganesh (2004); Goh et al. (2006); Hutchins (2000); Johnson (2002,2006); Johnson and Swisher (2003); Kuei and Madu (2003); Kumar et al.(2007); Kwak and Anbari (2006); McClusky (2006); Sahoo et al. (2008); Snee(2004) 29

(continued)Table II.

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Theme References Total

Project selection Antony (2004a, b, 2006); Antony et al. (2001, 2005, 2007c); Banuelas et al.(2006); Bonilla et al. (2008); Hu et al. (2008); Jung and Lim (2007); Kumar et al.(2007, 2008); Kumi and Morrow (2006); Kwak and Anbari (2006); Savolainenand Haikonen (2007); Su and Chou (2008) 16

Organizationalchange

Brewer (2004); Carnell and Lambert (2000); Craven et al. (2006); Davison andAl-Shaghana (2007); De Feo and Bar-El (2002); Fazzari and Levitt (2008);Immaneni et al. (2007); Llorens-Montes and Molina (2006); Lok et al. (2008);Motwani et al. (2004); Rajamanoharan and Collier (2006); Sadagopan et al.(2005); Schroeder et al. (2008); Thawani (2004) 14

Supply chain Antony et al. (2006); Bandyopadhyay and Jenicke (2007); Chan et al. (2006);Chappell and Peck (2006); Das (2005); Dasgupta (2003); Garg et al. (2004);Gowen (2005); Knowles et al. (2005); Wang et al. (2004); Yang et al. (2007);Yeh et al. (2007) 13

Six Sigmaeducation

Anderson-Cook et al. (2005); Cook et al. (2005); Edgeman and Dugan (2008);Ho et al. (2006); Maleyeff and Kaminsky (2002); Man (2002); Mitra (2004);Montgomery et al. (2005); Rao and Rao (2007); Stevenson and Mergen (2006);Weinstein et al. (2008) 11

Org. learning Box (2006); Jeffery (2005); Lin et al. (2008); Motwani et al. (2004); Ricondo andViles (2005); Savolainen and Haikonen (2007); Wiklund and Wiklund (2002) 7 Table II.

Figure 3.Distribution of Six Sigma

articles by themes

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Six Sigma methodologies (DMAIC and DFSS). The second largest part of Six Sigmaliterature deals with the theorization and application of Six Sigma methodologies.There are two major improvement methodologies in Six Sigma. The first methodology,DMAIC, is used to improve already existing processes and can be divided into fivephases; define, measure, analyze, improve and control. Several studies have shownsuccessful cases of DMAIC application in a variety of contexts such as healthcare(Dreachslin and Lee, 2007), thermal power plants (Kaushik and Khanduja, 2008),retailing (Kumar et al., 2008a), financial services (Kumar et al., 2008b) andmanufacturing process (Li et al., 2008; Tong et al., 2004). In contrast, the secondmethodology, design for Six Sigma (DFSS), is used for new processes or when theexisting processes are unable to achieve business objectives such as customersatisfaction (Andersson et al., 2006). DFSS methodology can also be divided into fivephases (DMADV); define, measure, analyze, design and verify (Banuelas and Antony,2003). Antony (2002) refers to DFSS as a powerful approach to design products andprocesses in a cost effective and simple manner. Applications of DFSS are also variedfrom high-tech manufacturing (Chung et al., 2008) to designing new housing (Johnsonet al., 2006a).

Six Sigma belt system. A part of Six Sigma structure is the role of Six Sigma leaderswho initiate, support and review improvement projects. Most Six Sigma organizationsadopt the hierarchical level of black belt and green belt systems. A black belt is afull-time team leader dedicated to the Six Sigma initiative. Black belts are equippedwith expertise in using the Six Sigma methodology and statistical analysis techniquesfor process improvement. Individuals at the highest level of expertise in Six Sigmamethodologies are called master black belts. They teach, coach and mentor thelower-level black belts and green belts. About 5 percent of employees in Six Sigmaorganization will be black belts, while the rest are trained to be green belts. Green beltsare project leaders and/or process experts who integrate Six Sigma into their daily jobduties. They are trained in the use the Six Sigma methodology and dedicatingapproximately 30 percent of their time toward Six Sigma initiatives. Most of theliterature on Six Sigma belt system focuses mainly on belts training and attributes.For example, Ingle and Roe (2001) contrasted the Six Sigma black belt programs usedin both Motorola and General Electric (GE). They concluded that GE has a morestructured approach to training black belts than does Motorola. The program in GE ismore intensive, takes a shorter time and therefore results in a greater number ofaccredited black belts. The authors also warn about the dangers of focusing on themetric rather than the mission in black belt training since some people were onlybecoming black belts in order to be promoted, and those that could not become blackbelts were resentful and disillusioned. With regard to black belts attributes, Antonyet al. (2007b) and Black and McGlashan (2006) found that several characteristics weremore essential than others in considering potential black belt candidates. The keyattributes of Six Sigma black belts in manufacturing companies include effectivecommunicators, change agents, customer advocators, team builders, results-drivenmindset personnel and positive thinkers. With regard to green belts, Green (2006a) andGreen et al. (2006) uses case studies to examine the nature of their training, work andthe projects in which they were involved.

Selection of Six Sigma projects. Selection of Six Sigma projects has receivedsubstantial attention from authors (e.g. Antony, 2004a; Banuelas et al., 2006; Hu et al.,

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2008; Jung and Lim, 2007; Kumar et al., 2007; Su and Chou, 2008) given that the rightselection of Six Sigma projects is one of the most critical factors for the effectivedeployment of a Six Sigma program. Antony (2004a) has indicated some projectselection criteria when a service organization wants to implement Six Sigma programs.Those criteria include financing, customer satisfaction, cost, risks and alignment ofstrategic business goals and objectives. If project selection is systematically sloppy, theentire Six Sigma effort could fail. Based on the results of a survey study, Banuelas et al.(2006) have pointed to project selection criteria employed in UK organizations. Thesecriteria include customer satisfaction, financial benefits, top management commitmentand the integration with the companys strategy. Moreover, Su and Chou (2008)employed three main steps for selecting Six Sigma projects. Those steps areunderstanding and analyzing the voice of customers (VOCs), drawing up theorganizations business strategic policies and deploying the possible Six Sigmaprojects based on the organizations business policies and the voice of customers. Theysuggest that Six Sigma projects can be prioritized based on evaluating benefits andrisks of each project. However, the prioritization of projects in many organizations isstill based on pure subjective judgment and very few powerful tools are available forprioritizing projects (Su and Chou, 2008). Cost benefit analysis, cause and effect matrix,brainstorming and Pareto analysis are among these tools and techniques which can beemployed to identify and prioritize such projects (Banuelas et al., 2006).

Six Sigma and quality approaches. Six Sigma literature has linked Six Sigma toquality approaches through two pivotal perspectives. The first perspective links SixSigma to TQM, while the second treats Six Sigma as a continuous improvementapproach. Within the first perspective, Six Sigma authors (e.g. Andersson et al., 2006;Black and Revere, 2006; Dahlgaard and Dahlgaard-Park, 2006; Ferng and Price, 2005;Furterer and Elshennawy, 2005; Green, 2006a; Ricondo and Viles, 2005) asserted thatSix Sigma is not an alternative to TQM.

Even though most Six Sigma tools and techniques are already being applied in theTQM field and both approaches preach that continuous improvement of quality isessential to business success, there is a vital distinction between them. Hence, theimpression raised by some researchers (e.g. Thirunavukkarasu et al., 2008) that SixSigma could be easily implemented in a company that implements TQM is stilldebatable. While authors regard TQM as a mushy management system consisting ofvalues, methodologies and tools that aims to improve customer satisfaction, theyconsider Six Sigma as a more structured methodology that fosters product and processimprovement so that the defects are never produced in the first place. Contrary toTQM, Six Sigma allows organizations to measure process capability and improvementefforts internally and externally. Schroeder et al. (2008) have identified four coreadvantages of Six Sigma over TQM. These advantages involve the focus on financialand business results, use of a structured method for process improvement or newproduct introduction, use of specific metrics such as DPMO, critical-to-quality (CTQ),and use of a significant number of full-time improvement specialists. According toAntony and Banuelas (2002), Ford found that Six Sigma is more profit orientated, whileTQM focuses on fixing the quality problem regardless of the cost. The abovementioned differences affirm the necessity of critical ingredients related to Six Sigmatraining, structure and focus to ensure successful transformation from TQM to SixSigma in an organization.

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On the other hand, Six Sigma has gained popularity as a continuous improvementstrategy aimed at reducing process-variations (Antony, 2002; Ehie and Sheu, 2005;Haikonen et al., 2004; Savolainen and Haikonen, 2007; Stewart and Spencer, 2006). Thisview is triggered through the link between the DMAIC-structure described above andthe Demings plan-do-check-act (PDCA) cycle. The idea in both procedural practicesforms a continuum over time for dynamic continuous improvement structure to sustainbusiness performance and bottom-line (Savolainen and Haikonen, 2007). Operationally,continuous improvement should be guided by Six Sigma tools and techniques fordefining specific process to be improved, analyzing root causes and designing actionsfor making improvement (Ehie and Sheu, 2005).

Six Sigma and lean production. Recent Six Sigma studies have focused on therelationship between Six Sigma and lean production (e.g. Andersson et al., 2006;Arnheiter and Maleyeff, 2005; Bendell, 2006; Chang and Su, 2007; Dahlgaard andDahlgaard-Park, 2006; Ferng and Price, 2005; Naslund, 2008; Pickrell et al., 2005) or onthe implementation of the new labeled concept Lean Six Sigma (e.g. Bonilla et al.,2008; Byrne et al., 2007; Cupryk et al., 2007; De Koning et al., 2006, 2008a, b; Furtererand Elshennawy, 2005; Gibbons, 2006; Marti, 2005).

The authors arrived at a conclusion that lean and Six Sigma complement each otherand represent a powerful framework for eliminating process waste and variation whenused together. Lean production is primarily concerned with eliminating waste andreducing cycle time in processes, but cannot reduce variation alone. Six Sigma canreduce variation and improve process by applying a problem-solving approach usingstatistical tools, but alone does not reduce waste or cycle time. Another distinctionbetween the two approaches is related to the scope. Whereas lean productionencompasses the entire organization value chain, Six Sigma concentrates morenarrowly on specific project or process within an organization. Despite thesedifferences, both approaches share common features that may combined together todevelop the Lean Six Sigma concept as an improvement methodology thatmaximizes shareholder value and improves customer satisfaction, cost, quality,process speed and invested capital by reducing variation and eliminating waste in anorganization (Byrne et al., 2007). Typically, some of lean Six Sigma cases that havebeen reported in the literature are applied in service settings including financial service(De Koning et al., 2008a, b), healthcare (De Koning et al., 2006), and local government(Furterer and Elshennawy, 2005).

Six Sigma success factors. Key factors for success or failure during Six Sigmaimplementation have always been subject to intensive literature (e.g. Antony, 2004b,2006; Antony and Fergusson, 2004; Antony and Banuelas, 2002; Antony et al., 2005;Buch and Tolentino, 2006b; Chakrabarty and Tan, 2007; Coronado and Antony, 2002;Kumar, 2007; Kwak and Anbari, 2006; McAdam and Evans, 2004a; Revere et al., 2006;Szeto and Tsang, 2005; Wessel and Burcher, 2004). The most cited success factors inSix Sigma literature include the following:

. Strong top management involvement and commitment.

. Selection of Six Sigma projects.

. Changing organizational culture.

. Aligning Six Sigma projects to corporate business objectives.

. Cross-functional team working.

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. Effective communication.

. Infrastructure (both organizational and IT infrastructure).

. Training.

. Linking Six Sigma to business strategy, customer, HRM, suppliers.

. Measurement.

. Accountability.

. Understanding tools and techniques within Six Sigma.

. Project management skills.

Benefits of Six Sigma. When Six Sigma is implemented successfully, it will offer adisciplined approach for improving effectiveness and efficiency in a broad range ofbusinesses. The most cited benefit of Six Sigma in the literature is customersatisfaction (e.g. Behara et al., 1995; Chen et al., 2005; Das et al., 2006; Desai, 2006;Douglas and Erwin, 2000; Ganesh, 2004; Kuei and Madu, 2003; Kumar et al., 2007;Rylander and Provost, 2006). Freiesleben (2006) suggested that successful applicationof Six Sigma quality is positively correlated with better financial performance andprofit generation. In the manufacturing context, Six Sigma benefits are related tovarious areas such as reduction in process variability, reduction in in-process defectlevels, reduction in maintenance inspection time, improving capacity cycle time,improving inventory on-time delivery, increasing savings in capital expenditures,increase in profitability, reduction of operational costs, reduction in the cost of poorquality (COPQ), increase in productivity, reduction of cycle time, reduction of customercomplaints, improved sales and reduced inspection (Antony et al., 2005, 2007a; Kwakand Anbari, 2006). Service organizations adopting Six Sigma strategy, on the otherhand, will have various benefits. According to Antony (2006, 2004a), Antony et al.(2007c), and Kwak and Anbari (2006), Six Sigma benefits for service organizations mayinvolve improved accuracy of resources allocation, improving accuracy of reporting,reduced documentary defects, improving timely and accurate claims reimbursement,streamlining the process of service delivery, reduced inventory of equipment, reducedservice preparation times, improved customer satisfaction, reduced defect rate inservice processes, reduced variability of key service processes, transformation oforganizational culture from fire-fighting mode to fire-prevention mode with theattitude of continuous improvement of service process performance, reduced processcycle time and hence achieve faster service delivery, reduced service operational costs,increased market share, improved cross-functional teamwork across the entireorganization, increased employee morale, reduced number of non-value added steps incritical business processes through systematic elimination, leading to faster delivery ofservice, reduced cost of poor quality (COPQ) (costs associated with late delivery,customer complaints, costs associated with misdirected problem solving, etc.),increased awareness of various problem solving tools and techniques, leading togreater job satisfaction for employees, improved consistency level of service throughsystematic reduction of process variability and effective management decisions due toreliance on data and facts rather than assumptions and gut-feelings.

Six Sigma challenges. Bridging the gap between the theory and practice in SixSigma research has been given more attention by Six Sigma researchers (e.g. Antony,2004b, 2007b, 2008b; Chakrabarty and Tan, 2007; Goh and Xie, 2004; McAdam et al.,

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2005; McAdam and Evans, 2004a, b; Nonthaleerak and Hendry, 2007; Senapati, 2004;Shahabuddin, 2008). Although its powerful strategy and impact on industry andservice sectors, Six Sigma still lacks a theoretical underpinning with othermanagement theory (Antony, 2008b). However, Linderman et al. (2003, 2006)attempt to enhance the underlying theory by linking Six Sigma to goal theory. Theydevelop a set of propositions that need further empirical verification. McAdam andEvans (2004a, b) have claimed that the Six Sigma program is weak in understandingcustomer needs and transforming these needs into products. Other Six Sigmalimitations are related to its application. These challenges and limitations as illustratedby Antony (2004b, 2007b, 2008b) are as follows:

. The 1.5 sigma shift resulting in a 3.4 DPMO does not make sense in serviceprocesses.

. The impact of leadership styles on Six Sigma success needs more research.

. No unified standards have been accepted regarding the contents of belt training.

. The relationship between the cost of poor quality (COPQ) and the sigma qualitylevel (SQL) is based on experience not empirical research.

. The relationship between COPQ and its financial impact in SMEs needs furtherresearch since SMEs are hardly considering quality costs.

. Availability of quality data is still a great challenge in Six Sigma projects.

. In some cases, the solutions driven by Six Sigma are expensive and only a smallpart of the solution is implemented at the end.

. Six Sigma project selection in many organizations is based on subjectivejudgment.

. The calculation of defect rates is based on the assumption of normality, while thecalculation of defect rates for non-normal situations is not yet properlyaddressed.

. Owing to dynamic market demands, critical-to-quality characteristics (CTQs)should be critically examined at all times and refined as necessary.

. Training programs usually do not address forecasting and time series methods.

. Six Sigma research needs to investigate the validity of 5 sigma approachassumption in design for Six Sigma (DFSS).

. There is no standard curriculum for Six Sigma in many top schools.

Six Sigma education. A series of Six Sigma papers have pointed to the entry of SixSigma program in an educational context. Edgeman and Dugan (2008) have arguedthat the pragmatic and intellectual focus of Six Sigma combined with tools andstrategies from engineering and business, develops a magnet curriculum that attractmany students. They have suggested two deployment approaches for its academicinstruction. The first approach is via central control at the unit, departmental, orcollege level for their own students and to attract students from other fields, while theother approach is via a radiant instructional model with core courses and electivecourses in discipline specific areas that match students needs. Moreover, Antony(2008b), Ho et al. (2006), Mitra (2004), and Rao and Rao (2007) believe that a Six Sigmaframework provides an excellent platform for integrating statistical, management and

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technical tools and skills into the curricula of engineering and business schools to helpstudents tackle business problems in organizations. Further, Rao and Rao (2007)suggested that all students of management must leave the institution as certified blackbelts. Maleyeff and Kaminsky (2002) and Cook et al. (2005) have revealed a positivefeedback from students regarding a course on Six Sigma taught at US universities.However, successful academic adoption of Six Sigma curricula require not only finecontent, but also its organization and supporting culture that rely in part on intellectualand practical experiences from external contributors such as Six Sigma black belts(Edgeman and Dugan, 2008).

Six Sigma and organizational change. Many authors have seen Six Sigma as anorganizational change vehicle that possesses a culture of accountability, quality, andinnovation (Brewer, 2004; Carnell and Lambert, 2000; Craven et al., 2006; Davison andAl-Shaghana, 2007; Immaneni et al., 2007; Lok et al., 2008). Schroeder et al. (2008)suggested that Six Sigma should be viewed as an organization change process. Theview will improve Six Sigma implementation through identifying what needs to bechanged and boost change management process itself. Thawani (2004) revealed thatSix Sigma has been deployed strategically to change the culture of organizationthrough inculcating process control discipline in business context. The main issue isthat organizations need to know when and how changes can be made to deploy SixSigma tools. Sadagopan et al. (2005) suggested three Six Sigma transitions (i.e.physical, psychological, and mindset) which are required for successfulimplementation of Six Sigma program. These transitions ensure changes inresources, employees and management to facilitate the implementation of alternativeprocesses that achieve 3.4 DPMO in organizational performance. In the same vein,Llorens-Montes and Molina (2006) suggested that the implementation of a Six Sigmaprogram needs successful change management of behavioral and work processes toachieving planned aspirations. Moreover, Rajamanoharan and Collier (2006) usedchange management model as a framework to explore Six Sigma implementationissues. They indicated that successful change management can be facilitated byleadership support, learning capacity and IT leveragability while a low level of culturalreadiness and an inadequate knowledge-sharing capability inhibits successful change.A success story of organizational transformation process to implement Six Sigma inDow Chemicals has been reported by Motwani et al. (2004).

Six Sigma and supply chain. Several studies have investigated how Six Sigmamethodology can effectively be employed in supply chain management (SCM) to measure,monitor and improve the performance of the whole supply network. For example,Dasgupta (2003) called for the application of Six Sigma metrics as a comprehensive andflexible framework for evaluating and benchmarking the performance of a supply chainand its entities against world-class standards. Wang et al. (2004) developed an applicationguideline for the assessment, improvement and control of quality in SCM in Taiwan usingSix-Sigma improvement methodology. They advocated that improvements in the qualityof all supply chain processes lead to cost reductions as well as service enhancements.Although they demonstrated that Six Sigma has not been successfully adapted to deliversimilar benefits across supply chains, Knowles et al. (2005) concluded that Six Sigma doeshave something novel to offer organizations over the contribution of existing approaches tosupply chain improvement. They proposed a conceptual model that integrates theBalanced Scorecard, SCOR model (Supply Chain Reference model) and Six Sigma DMAIC

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methodology in a strategic- and operational-level cycles. Chappell and Peck (2006)concluded that Six Sigma can be applied to supply chains by following the DMAICframework and employing a mixture of quantitative and qualitative tools. However, theyalso suggest that it is difficult to implement Six Sigma methodology throughout the supplychain under some circumstances related to stock holding policies and levels of demand.Furthermore, Antony et al. (2006) proposed a Six Sigma constrained genetic algorithm(GA) based heuristic to optimize supply chain performance through the synchronization ofthe business processes. The suggested model aimed at minimizing the total cost andensuring very high delivery probability within the customer specified delivery window. Inthe same scene, Garg et al. (2004) introduced Six Sigma supply chains as a new notion todescribe and quantify supply chains with sharp and timely deliveries. Using inventoryoptimization (IOPT) problem, they show that the design of Six Sigma supply chains candeliver products within a customer specified delivery window, with at most 3.4 misseddeliveries per million. Presenting a real industry case about Six Sigma methodology for theSCM, Yang et al. (2007) argued how the black belt program in Samsung has producedhighly qualified and talented SCM specialists, who are currently training the methodologyto members in their organizations and leading SCM projects. As a result, SCM projects inSamsung are prepared and conducted in a more disciplined way and their outcomes arecontinuously monitored and shared through the companys repository.

Six Sigma and organizational learning. Few studies have looked at the link betweenSix Sigma and organizational learning from a perspective that Six Sigma methodologiesare mature enough to be integrated with different learning approaches. Wiklund andWiklund (2002) discussed Six Sigma as a company-wide approach for organizationalimprovement incorporating organizational learning. The authors covered the factors thatare essential for improving organizational learning and for stimulating the competence,development and motivation among personnel. Further, Ricondo and Viles (2005)considered Six Sigma as an improvement program that can be linked to organizationallearning under certain conditions depending on their problem-solving capabilities.Savolainen and Haikonen (2007) examined the dynamics of organizational learning in thecontext of Six Sigma implementation in organizations. They suggested that learning inSix Sigma implementation is a single-loop and incremental type where the learningprocess is characterized by measurement, detection and correction of errors and costreduction. Consequently, continuous improvement occurs through procedural practiceslike in the DMAIC-cycle that forms a structure for sustained learning process.

Distribution of articles by research method. The distribution of articles by researchmethod is shown in Table III. About 63 percent of the articles (263 articles) wereclassified as empirical articles using either surveys or case studies, while about 37percent of the articles (154 articles) were theoretical articles that usually employextensive literature review to focus on the development of concepts, propositions,models, or theory building. Also, it is clear that case study is the most dominantresearch method in Six Sigma articles (231 articles, 55.4 percent). Figure 4 shows thegrowing gap over the years between case study method and other research methods,particularly survey research. Case study method is used to document and analyze SixSigma implementation in particular contexts; industry, service, process or phase of aspecific project. Examples of Six Sigma case study research include Desai (2006)concerning applying Six Sigma approach to improve customer service in an Indiansmall scale industry, Echempati and White (2000) regarding analyzing hinge

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TotalMethod References n %

Case-focusedarticles

Adams et al. (2004); Agarwal and Bajaj (2008); Al-Aomar (2006); Al-Mishariand Suliman (2008); Amer et al. (2007, 2008); Anand et al. (2007); Antony andFergusson (2004); Antony et al. (2007c); Arul and Kohli (2004);Bandyopadhyay and Jenicke (2007); Bandyopadhyay and Lichtman (2007);Banuelas and Antony (2003); Banuelas et al. (2005); Bayle et al. (2001); Beard(2008); Behara et al. (1995); Benedetto (2003); Bigio et al. (2004); Bonilla et al.(2008); Box (2006); Brett and Queen (2005); Brewer (2004); Brewer andEighme (2005); Bunce et al. (2008); Byrne (2003); Camgoz-Akdag (2007); Chanet al. (2005); Chang and Su (2007); Chappell and Peck (2006); Chatterjee (2003);Chen et al. (2005a, b, 2007, 2008); Cheng et al. (2008a); Craven et al. (2006);Cupryk et al. (2007); Das (2005); Das and Hughes (2006); Dasgupta (2003);Davison and Al-Shaghana (2007); De Koning et al. (2006, 2008a, b); De Vore(2008); Desai (2006, 2008); Doble (2005); Does et al. (2002); Douglas and Erwin(2000); Dreachslin and Lee (2007); Drenckpohl et al. (2007); Echempati andWhite (2000); Edgeman et al. (2005); Ehie and Sheu (2005); Elberfeld et al.(2007); Eldridge et al. (2006); Erlandson (2006); Ferng and Price (2005); Frank(2003); Frankel et al. (2005); Furterer and Elshennawy (2005); Garg et al.(2004); Gerhorst et al. (2006); Gibbons (2006); Gijo and Rao (2005); Goel andChen (2008); Goh (2001, 2002b); Goh et al. (2003); Gowen (2008); Green (2006a);Green et al. (2006); Hagemeyer et al. (2006); Haikonen et al. (2004); Hamza(2008); Han and Lee (2002); Harjac et al. (2008); Harrington and Trusko (2005);Hasenkamp and Olme (2008); Henderson and Evans (2000); Hendricks andKelbaugh (1998); Hensley and Dobie (2005); Hild et al. (2000); Hilton et al.(2008); Ho and Chuang (2006); Ho et al. (2006, 2008); Holtz and Campbell(2004); Hong and Goh (2003, 2004); Hsu et al. (2008); Hu and Antony (2007);Hu and Pieprzak (2005); Hwang (2006); Immaneni et al. (2007); Ingle and Roe(2001); Isaacson (2008); Jenicke et al. (2008); Jin et al. (2008); Johnson (2002,2006); Johnson and Swisher (2003); Johnson et al. (2006a, b, c); Johnston et al.(2008); Johnstone et al. (2003a, b); Jung and Lim (2007); Juras et al. (2007);Kalamdani and Khalaf (2006); Kapur and Feng (2005); Kaushik andKhanduja (2008); Kaushik et al. (2008); Khalaf and Yang (2006); Knowles et al.(2004); Kovach (2007); Kovach and Cho (2006); Krishna and Dangayach(2007); Krishna et al. (2008); Kumar (2007); Kumar et al. (2006, 2007, 2008a, b);Kumi and Morrow (2006); Ladani et al. (2006); Lee-Mortimer (2006, 2007); Liand Al-Refaie (2008); Li et al. (2006, 2008); Lin et al. (2008); Lipscomb andLewis (2004); Liu et al. (2008); Lloyd (2006); Lok et al. (2008); Lucier andSeshadri (2001); McAdam and Lafferty (2004); Mahanti and Antony (2005,2006); Mahesh et al. (2006); Malhan and Rao (2005); Malliga and Srinivasan(2007); Manikandan et al. (2008); Markarian (2004a, b); Marti (2005); Martinet al. (2006); Mazzola et al. (2007); Mekki (2006); Miles (2006); Morgan andCooper (2004); Morusca and Cupryk (2005); Motwani et al. (2004);Mukhopadhyay and Ray (2006); Murugappan and Keeni (2003); Neagu andHoerl (2005); Neri et al. (2008); Ng et al. (2005); Nonthaleerak and Hendry(2008); ONeill (2005); Pan and Cheng (2008); Pandey (2007); Patterson et al.(2005); Perng et al. (2008); Perry and Barker (2006); Pheng and Hui (2004);Pickrell et al. (2005); Proudlove et al. (2008); Rajagopal and Castillo (2007);Rajagopalan et al. (2004); Rasis et al. (2002a); Rasis et al. (2002b);Ravichandran (2006, 2008); Revere and Black (2003); Revere et al. (2004);Sadagopan et al. (2005); Sahoo et al. (2008); Sarkar (2007a, b); Savage (2007);Savage and Son (2008); Savolainen and Haikonen (2007); Sehwail and DeYong (2003); Sekhar and Mahanti (2006); Setijono (2008); Shahin (2008);Sharma (2003); Smith (1993); Sokovic et al. (2005); Stewart and Spencer(2006); Su and Chou (2008); Su et al. (2006); Su et al. (2005); Sudhahar et al.(2008); Taghaboni-Dutta and Moreland (2004); Tang et al. (2007); Tannocket al. (2007); Thakkar et al. (2006); Thiele et al. (2008); Thomas and Barton(2006); Thomas and Lewis (2007); Thomas et al. (2008a, b); Thomas andSingh (2006); Thompson et al. (2008); Tong et al. (2004); Ung et al. (2007); VanDen Heuvel et al. (2004, 2005, 2006); Van Iwaarden et al. (2008); Vaughan(1998); Vote and Huston (2005); Wang et al. (2004); Woodall (2001); Woodard(2005, 2006); Wright and Basu (2008); Wyper and Harrison (2000); Xue-Lianget al. (2007); Yang and Yeh (2007); Yang et al. (2007); Yeh (2007); Yeung, V.(2007); Zaroukian and Sierra (2006); Zhan (2008); Zhang and Xu (2008) 231 55.4

(continued )

Table III.Classification of Six

Sigma articles byresearch method

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alignment problems using six-sigma quality, Furterer and Elshennawy (2005) onimplementing TQM and lean Six Sigma tools in local government, Gerhorst et al. (2006)about using DFSS in product development at Ford Motor Company and Knowles et al.(2004) on Six Sigma application at a UK food manufacturer. The analysis is typicallynarrow, in-depth and provides a thorough examination of a limited Six Sigma area.Some case study articles represent anecdotal examples of Six Sigma practices, withoutexploring practice in any rigorous or in-depth manner. On the contrary, surveysrepresent the least dominant research method in Six Sigma articles (32 articles, 7.7percent) where typical wide perspective or superficial generalization are employed to a

TotalMethod References n %

Review-focusedarticles

Aggogeri and Gentili (2008); Al-Aomar and Youssef (2006); Anderson-Cooket al. (2005); Andersson et al. (2006); Antony (2002, 2004b, 2006, 2007a, b,2008b); Antony and Banuelas (2002); Antony et al. (2006); Arnheiter andMaleyeff (2005); Banuelas and Antony (2004); Basu (2004); Bellows (2004);Bendell (2006); Biedry (2001); Biehl (2004); Bisgaard and Freiesleben (2000);Black and McGlashan (2006); Box and Luceno (2000); Brady and Allen (2006);Brewer and Bagranoff (2004); Byrne et al. (2007); Card (2000); Carnell andLambert (2000); Carrigan and Kujawa (2006); Caulcutt (2001); Chan et al.(2006); Cook et al. (2005); Coronado and Antony (2002); Cronemyr (2007);Dahlgaard and Dahlgaard-Park (2006); Das et al. (2006); De Feo (2000); DeFeo and Bar-El (2002); De Koning and De Mast (2005, 2006); De Mast (2006,2007); Dedhia (2005); Delsanter (1992); Edgeman and Dugan (2008);Fairbanks (2007); Fazzari and Levitt (2008); Feld and Stone (2002); Ferryanto(2007); Flott (2000); Foster (2007); Freiesleben (2006, 2007); Friday-Stroud andSutterfield (2007); Fuller (2000a, b); Gack and Robison (2003); Ganesh (2004);Garg et al. (2004); Glower (2006); Goeke and Offodile (2005); Goh (2002a); Gohand Xie (2003, 2004); Goh et al. (2006); Graves (2002); Green (2006b); Gremyr(2005); Hahn (2005); Hahn et al. (1999, 2000); Hammer (2002); Hare (2005);Hoerl (1998, 2004); Hoerl et al. (2001); Hsieh et al. (2007); Hu et al. (2005, 2008);Huq (2006); Hutchins (2000); Ingram (2000a, b, c); Jeffery (2005); Johnson(2006); Kanji (2008); Kleasen (2007); Klefsjo et al. (2001, 2006); Knowles et al.(2005); Kuei and Madu (2003); Kumar, M. et al. (2008); Kumar, U. et al. (2008);Kwak and Anbari (2006); Lanyon (2003); Lee and Choi (2006); Linderman et al.(2006); Linderman et al. (2003); Little (2003); Llorens-Montes and Molina(2006); Lupan et al. (2005); McAdam et al. (2005); McCarty and Fisher (2007);McClusky (2006); Mahanti (2005); Maleyeff and Kaminsky (2002); Maleyeffand Krayenvenger (2004); Man (2002); Manual (2006); Markarian (2004a, b);Mitra (2004); Montgomery et al. (2005); Moorman (2005); Naslund (2008);Nonthaleerak and Hendry (2006, 2007); Pfeifer et al. (2004); Pojasek (2003);Prabhushankar et al. (2008); Raisinghani et al. (2005); Rajamanoharan andCollier (2006); Rao and Rao (2007); Ravichandran (2007); Ribardo and Allen(2003); Ricondo and Viles (2005); Rudisill and Clary (2004); Rylander andProvost (2006); Sanders and Hild (2000a, b, c); Schroeder et al. (2008);Senapati (2004); Shah et al. (2008); Shahabuddin (2008); Shahin and Alinavaz(2008); Shanmugam (2007); Smith and Phadke (2005); Snee (2004); Sodhi andSodhi (2005); Stevenson and Mergen (2006); Thawani (2004);Thirunavukkarasu et al. (2008); Treville et al. (2008); Vestal (2004); Walters(2005); Weinstein et al. (2008); Wiklund and Wiklund (2002); Yang, C. (2004);Yang, K. (2004, 2005); Yeung (2007); Yilmaz and Chatterjee (2000); Zu et al.(2008) 154 36.9

Survey-focusedarticles

Antony (2004a, 2008a); Antony et al. (2001, 2005, 2007a, b, 2008); Banuelaset al. (2006); Bhatnagar and Pandey (2005); Black and Revere (2006); Buchand Tolentino (2006a, b); Chakrabarty and Tan (2007); Chang and Wang(2008); Cheng (2007a, b, c, 2008); Chung et al. (2008); Feng and Manuel (2008);Frings and Grant (2005); Gowen (2005); Kumar et al. (2007);Laosirihongthong et al. (2006); McAdam and Evans (2004a, b); Revere et al.(2006); Schon (2006); Szeto and Tsang (2005); Taner et al. (2007); Wessel andBurcher (2004); Yang et al. (2008) 32 7.7Table III.

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large number of cases. Examples of Six Sigma survey research involve Feng andManuel (2008) who conducted a national survey of Six Sigma programs in UShealthcare organizations, Antony (2004a) regarding Six Sigma application in UKservice organizations, Antony et al. (2005) concerning Six Sigma implementation inmanufacturing SMEs in the UK, and Black and McGlashan (2006) on essentialcharacteristics of Six Sigma black belt candidates in US companies.

Distribution of articles by sector: manufacturing vs serviceAccording to this distribution, empirical Six Sigma articles (263 articles, 63.3 percent)are broken down into two major sectors; manufacturing and service. Table IV showsthat the majority of empirical articles are deemed to be manufacturing-focused (169articles, 64.3 percent). This category comprises articles examining Six Sigma withinmanufacturing contexts such as semiconductor (e.g. Su and Chou, 2008; Su et al., 2005),automotive (e.g. Chen et al., 2005; Krishna et al., 2008; Kumar et al., 2007), aerospace(e.g. Maleyeff and Krayenvenger, 2004), chemical (e.g. Motwani et al., 2004; Doble,2005), software (e.g. Antony and Fergusson, 2004; Hong and Goh, 2003, 2004; Mahanti,2005; Mahanti and Antony, 2005, 2006), pharmaceutical (e.g. Cupryk et al., 2007;Morusca and Cupryk, 2005), steel (e.g. Sarkar, 2007a, b) and aluminum (e.g. Das andHughes, 2006) industries. On the contrary, service-focused articles constitute the leastpublished empirical articles in Six Sigma (52 articles, 34 percent). Healthcare context,however, is the most dominant setting in the service category. Examples of Six Sigmaarticles in healthcare include Antony et al. (2007c), De Koning et al. (2006), Dreachslinand Lee (2007), Feng and Manuel (2008), Harrington and Trusko (2005), Jin et al. (2008),Johnstone et al. (2003a), Lloyd and Holsenbach (2006), Proudlove et al. (2008), andTaner et al. (2007). Other service contexts may include government (e.g. Furterer andElshennawy, 2005; Ho and Chuang, 2006), banking (e.g. Immaneni et al., 2007), andeducation (e.g. Thakkar et al., 2006; Weinstein et al., 2008). Table IV provides acomprehensive list containing classified references for each of Six Sigma application

Figure 4.Distribution of Six Sigma

articles by researchmethod (1992-2008)

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TotalSector References n %

Manufacturing-focused

Agarwal and Bajaj (2008); Al-Mishari and Suliman (2008); Amer et al.(2007, 2008); Anand et al. (2007); Antony (2008a); Antony andFergusson (2004); Antony et al. (2005, 2007a, b, 2008); Arul and Kohli(2004); Bandyopadhyay and Jenicke (2007); Banuelas and Antony(2003); Banuelas et al. (2005, 2006); Bayle et al. (2001); Bhatnagar andPandey (2005); Black and Revere (2006); Brewer (2004); Buch andTolentino (2006a, b); Bunce et al. (2008); Byrne (2003); Camgoz-Akdag(2007); Chang and Wang (2008); Chatterjee (2003); Chen et al. (2005,2007); Cheng (2007a, b, c); Cheng et al. (2008a); Chung et al. (2008b);Cupryk et al. (2007); Das (2005); Das and Hughes (2006); Dasgupta(2003); Davison and Al-Shaghana (2007); De Vore (2008); Desai (2006);Doble (2005); Echempati and White (2000); Ehie and Sheu (2005);Erlandson (2006); Gerhorst et al. (2006); Gibbons (2006); Gijo and Rao(2005); Goel and Chen (2008); Goh (2001); Goh (2002b); Gowen (2005);Green (2006a); Green et al. (2006); Hagemeyer et al. (2006); Haikonenet al. (2004); Hamza (2008); Han and Lee (2002); Harjac et al. (2008);Hasenkamp and Olme (2008); Henderson and Evans (2000);Hendricks and Kelbaugh (1998); Hild et al. (2000); Ho et al. (2008);Holtz and Campbell (2004); Hong and Goh (2003, 2004); Hsu et al.(2008); Hu and Antony (2007); Hu and Pieprzak (2005); Hwang (2006);Ingle and Roe (2001); Johnson (2002); Johnson and Swisher (2003);Johnson et al. (2006b, c); Johnston et al. (2008); Jung and Lim (2007);Kalamdani and Khalaf (2006); Kapur and Feng (2005); Kaushik andKhanduja (2008); Kaushik et al. (2008); Khalaf and Yang (2006);Knowles et al. (2004); Kovach and Cho (2006); Krishna andDangayach (2007); Krishna et al. (2008); Kumar (2007); Kumar, M et al.(2006, 2007); Kumar, U. et al. (2007); Ladani et al. (2006); Lee-Mortimer(2006); Lee-Mortimer (2007); Li et al. (2008); Li and Al-Refaie (2008); Liet al. (2006); Lin et al. (2008); Liu et al. (2008); Lok et al. (2008); Lucierand Seshadri (2001); McAdam and Evans (2004a, b); McAdam andLafferty (2004); Mahanti and Antony (2005); Mekki (2006); Mahantiand Antony (2006); Mahesh et al. (2006); Maleyeff and Kaminsky(2002); Manikandan et al. (2008); Markarian (2004a, b); Mazzola et al.(2007); Miles (2006); Morusca and Cupryk (2005); Motwani et al.(2004); Mukhopadhyay and Ray (2006); Murugappan and Keeni(2003); Neagu and Hoerl (2005); Nonthaleerak and Hendry (2008); Panand Cheng (2008); Pandey (2007); Patterson et al. (2005); Perng et al.(2008); Pickrell et al. (2005); Rajagopal and Castillo (2007);Rajagopalan et al. (2004); Rasis et al. (2002a, b); Ravichandran (2008);Revere et al. (2006); Sadagopan et al. (2005); Sahoo et al. (2008); Sarkar(2007a, b); Savage (2007); Savage and Son (2008); Savolainen andHaikonen (2007); Schon (2006); Sekhar and Mahanti (2006); Setijono(2008); Shahin (2008); Sharma (2003); Smith (1993); Sokovic et al.(2005); Su and Chou (2008); Su et al. (2005); Sudhahar et al. (2008);Szeto and Tsang (2005); Tang et al. (2007); Tannock et al. (2007);Thomas and Barton (2006); Thomas and Lewis (2007); Thomas et al.(2008a, b); Thomas and Singh (2006); Tong et al. (2004); Ung et al.(2007); Van Iwaarden et al. (2008); Vaughan (1998); Wang et al. (2004);Wessel and Burcher (2004); Wright and Basu (2008); Wyper andHarrison (2000); Yang and Yeh (2007); Yang et al. (2007, 2008); Yeh(2007); Yeh et al. (2007); Zhan (2008) 169 64.3

(continued )

Table IV.Classification of SixSigma articles byapplication sector

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TotalSector References n %

Service-focused Adams et al. (2004); Al-Aomar (2006); Antony (2004a); Antony et al.(2001, 2007c); Bandyopadhyay and Lichtman (2007); Beard (2008);Behara et al. (1995); Benedetto (2003); Bigio et al. (2004); Bonilla et al.(2008); Box (2006); Brett and Queen (2005); Brewer and Eighme(2005); Chakrabarty and Tan (2007); Chan et al. (2005); Chang andSu (2007); Chappell and Peck (2006); Chen et al. (2005, 2008); Cheng(2008); Craven et al. (2006); De Koning et al. (2006, 2008a, b); Desai(2008); Does et al. (2002); Douglas and Erwin (2000); Dreachslin andLee (2007); Drenckpohl et al. (2007); Edgeman et al. (2005); Elberfeldet al. (2007); Eldridge et al. (2006); Feng and Manuel (2008); Ferngand Price (2005); Frank (2003); Frankel et al. (2005); Frings andGrant (2005); Furterer and Elshennawy (2005); Garg et al. (2004);Goh et al. (2003); Gowen (2008); Harrington and Trusko (2005);Hensley and Dobie (2005); Hilton et al. (2008); Ho and Chuang (2006);Ho et al. (2006); Immaneni et al. (2007); Isaacson (2008); Jenicke et al.(2008); Jin et al. (2008); Johnson et al. (2006a); Johnstone et al.(2003a, b); Juras et al. (2007); Kovach (2007); Kumar et al. (2008a, b);Kumi and Morrow (2006); Lipscomb and Lewis (2004); Lloyd (2006);Malhan and Rao (2005); Malliga and Srinivasan (2007); Marti (2005);Martin et al. (2006); Morgan and Cooper (2004); Neri et al. (2008); Nget al. (2005); ONeill (2005); Perry and Barker (2006); Pheng and Hui(2004); Proudlove et al. (2008); Ravichandran (2006); Revere andBlack (2003); Revere et al. (2004); Sehwail and De Yong (2003);Stewart and Spencer (2006); Snee (2004); Taghaboni-Dutta andMoreland (2004); Taner et al. (2007); Thakkar et al. (2006); Thieleet al. (2008); Thompson et al. (2008); Van Den Heuvel et al. (2004,2005, 2006); Vote and Huston (2005); Woodall (2001); Woodard(2005, 2006); Wright and Basu (2008); Yeh (2007); Yeung (2007);Zaroukian and Sierra (2006) 94 35.7 Table IV.

Figure 5.Distribution of Six Sigma

articles by applicationsector (1992-2008)

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289

contexts. Figure 5 demonstrates the growing gap between manufacturing andservice focused Six Sigma research over years.

Conclusions and future research directionsOur conclusions are based on the analysis of 417 Six Sigma articles that werepublished in 147 journals over a 17-year period from 1992 to 2008. Overall, we haveobserved that Six Sigma research has attracted the attention of both practitioners andacademics. In particular, research activities on Six Sigma have increased significantlyafter 1999. The trend implies that more than 98 percent of Six Sigma articles werepublished between 2000 and 2008. Clearly Six Sigma research is difficult to confine tospecific discipline since it is scattered across various journals from various domainsand fields.

The review has observed that Six Sigma research is empirical in nature whichreinforces the use of real-world data. Case study was the dominant approach in SixSigma research and this is may be due to the fact that quality problems inmanufacturing and service contexts are usually treated as a case in terms ofdocumentation and analysis. In addition, the lack of implementing Six Sigma tools andmethodologies across a wide range of processes or organizations makes the use ofsurvey approach impractical.

Although modifications have been made in the Six Sigma framework to extend itsapplication from manufacturing to service context, the increasing gap between thenumbers of manufacturing and service focused Six Sigma articles since 2005implies the return of Six Sigma to manufacturing as its initial base.

Although this review does not claim to be exhaustive, it does provide reasonableinsights into the state of the art in Six Sigma research. One of the most significantfindings from our analysis has been the great empirical focus on Six Sigma tools andtechniques. There is very little room for clarifying the confusion in the literature as towhat constitutes Six Sigma theory and how does it integrate with other improvementstrategies. We would argue that theoretical development is critical to the developmentof Six Sigma studies. Based on the literature review presented in this paper, we identifybelow a number of research implications and directions for future research as follows:

. There is no doubt that Six Sigma research will grow rapidly in future coveringvarious disciplines and domains. Hence, there is a need to construct and clearlypresent the application of Six Sigma within each domain in a proposedframework or generic model.

. It is not surprising that a large portion of the reviewed articles in this study wererelated to Six Sigma tools, techniques, and methodologies. This reflects theresearchers concern of the core nature of Six Sigma as a more structured qualityapproach compared to TQM. Detailed analysis of these tools and methodologieswithin manufacturing and service contexts is required.

. We expect more research to be conducted on user experiences reflecting SixSigma pros and cons in such context.

. While researchers try to develop new Six Sigma applications, the capabilities ofuser infrastructure need to be considered.

. More theory based empirical research is needed to enhance the construction ofSix Sigma theory.

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. There is a great potential for practicable application of survey approach in SixSigma research as a wide range of processes or organizations adopt Six Sigmatools and methodologies.

. Since the combined use of analytical and empirical research techniques has thepotential to offer greater insights into research, it is desirable to see more papersapply triangulation approach in Six Sigma research through the use of multipledata collection methods.

. Researchers are encouraged to map the efforts of Six Sigma research inmanufacturing and service organizations to a proposed framework and thenprovide a through analysis on each framework.

. Researchers and practitioners are encouraged to propose a standard Six Sigmacurriculum design with multidisciplinary orientation.

. Managing Six Sigma risks and crises is a new attractive topic for researchers.

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