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Six Sigma: a literature review
Article in International Journal of Lean Six Sigma · August 2010
DOI: 10.1108/20401461011075017
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Six Sigma: a literature review
B Tjahjono*, P Ball, V I Vitanov, C Scorzafave, J Nogueira, J Calleja, M Minguet, L
Narasimha, A Rivas, A Srivastava, S Srivastava and A Yadav
Manufacturing Department, School of Applied Sciences, Cranfield University,
Cranfield, Bedford MK43 0AL, UK
Abstract
Purpose: The purpose of the work presented in this paper is to capture the current
state of Six Sigma as well as to document the current practices of Six Sigma through a
systematic literature review so as to extend and update the previous work of Brady and
Allen (2006).
Design/methodology/approach: The approach to this research is to answer the
questions such as what is Six Sigma?, what are the applications of the Six Sigma?,
what are the main enablers and barriers to its application?, and what are the emerging
trends? These questions are used to guide the search of papers from various
publication databases even if it is expected that existing literature might not be
sufficiently developed to translate each question directly into a finding. The literature is
then analysed and the major emerging themes are presented.
Findings: Seven key findings (topics on which the views of the authors converged) and
two issues (topics on which authors had differing views) have been established. These
include the interpretation of Six Sigma, tools and techniques, implementation of Six
Sigma, benefits, adoption, enablers and links to other disciplines.
Originality/value: The systematic literature review approach used in this paper allows
emerging trends and issues in Six Sigma to be highlighted in a structured and thematic
manner, enabling the future work to progress as Six Sigma continues to develop and
evolve. The findings also open up new opportunities to apply Six Sigma in the fields
that are not widely explored before for instance sustainability and Product-Service
Systems (PSS).
Keywords: Six Sigma, literature review, DMAIC, DFSS, process improvement
Paper type: Literature review
*Corresponding author
Address: Building 50, Manufacturing Department, School of Applied Sciences,
Cranfield University, Cranfield, Bedford MK43 0AL, UK
Phone: +44 1234 750111 ext 5453
Email: b.tjahjono@cranfield.ac.uk
1
1.
Introduction
Since the introduction of the initial six-step process by Motorola University Design for
Manufacturing training programme in 1988 (Watson and DeYong, 2010), Six Sigma
has evolved to become an extension to Total Quality Management (TQM) (Green,
2006). As a project-driven management approach, the range of Six Sigma applications
is also growing from reduction of defects in an organisation’s processes, products and
services, to become a business strategy that focuses on improving understanding of
customer requirements, business productivity and financial performance (Kwak and
Anbari, 2006). Six Sigma has branched out initially from the electronics industries (e.g.
Motorola and Texas Instruments) to many other sectors. In the last two decades, this
growth has become more prevalent as Six Sigma principles have also been
implemented in service industries in the context of supply chain (Arnheiter & Maleyeff,
2005; Wei et al, 2010), as well as hospitals (Sehwail & DeYong, 2003; van den Heuvel
at al, 2005), local government (Furterer & Elshennawy, 2005) and public sectors (Patel,
S.C. and Zu, 2009; Kumar & Bauer, 2010).
The purpose of this paper is therefore to capture the state-of-the-art within the Six
Sigma philosophy as well as to document notable development of practices through a
systematic literature review. The methodology includes targeting relevant publications
databases, searching these using a wide range of keywords and phrases associated
with Six Sigma, and then reviewing each paper identified. The outcome of these
reviews was the extraction of a set of key findings, compiled and grouped by topics.
2.
Research programme
2.1
Scope and research questions
This review of literature, to a large extent, aims to extend the work of Brady and Allen
(2006) who incorporated Six Sigma publications from 1990 to 2003 and complement
2
their findings. For this reason, the systematic literature review in this paper considers a
defined time frame from 2004 to 2009. To provide a global vision of the subject matter,
the scope of this work is not limited in terms of industrial sectors considered but only in
terms of the type of sources used, i.e. from journal publications from established
databases.
The initial approach to this research was to answer the following questions:
1. What is Six Sigma?
2. What are the applications of the Six Sigma?
3. What are the main enablers and barriers to its application?
4. What are the emerging trends?
The purpose of these questions was to guide the search even if it was expected that
existing literature might not be sufficiently developed to translate each question directly
into a finding.
2.2
Search strategy
The search strategy was developed by first identifying the relevant data sources and
keywords. The databases included Scopus, ABI/Inform, IEEE Xplore and Emerald. The
time frame was chosen initially to include only the literature published between 2004
and 2009, however, as the research progressed, this was extended as a result of cross
citations to include papers from 2000.
The search set out by choosing a set of keywords and possible combinations that could
be significant to Six Sigma. The concept of Six Sigma embraces a very wide range of
aspects and so a considerable number of search strings were deemed necessary.
These captured all the aspects that characterise Six Sigma, such as definition,
methodology, techniques, tools, implementation, enablers and issues. Keywords
3
related to other important concepts to analyse possible connections were also used.
Examples of these include lean, supply chain management, process management and
sustainability.
Table 1 shows the number of items associated with some of the search strings used. It
shows the publications related to the implementation of Six Sigma, the associated tools
and techniques and the DMAIC methodology. Also quite developed in literature is the
topic of “Lean and Six Sigma”. Perhaps surprisingly, the keywords “Six Sigma +
sustainability” only retrieved 12, although the concept of sustainable production was
presented almost 30 years ago (Miron and Skarke, 1981).
Table 1 – Keywords search results
Keywords
S1
S2
S3
S4
S5
S6
S7
S8
S9
S10
Six Sigma + definition
Six Sigma + implementation
DMAIC
DFSS
Six Sigma + Tools OR Techniques
Six Sigma + simulation
Six Sigma + sustainability
Six Sigma + TQM
Six Sigma + Lean
Six Sigma + Supply Chain
Journal papers
(Scopus+ABI)
12+14
114+100
83+56
46+19
207+145
30+12
7+5
27+55
108+123
18+16
The main exclusion criterion in this search was to take into account only papers
focused primarily on Six Sigma, ignoring consequently the ones that cited it as
methodology used but did not go in depth in the dissertation about it.
2.3
Results and analysis
The search strategy initially identified 210 publications. However, each work was
checked by first reading the abstracts so that those that appeared to be outside the
scope of the review, because of the vagueness and lack of detail for instance, were
excluded. Following the screening, the papers were reduced to 167 as a result from
more thorough examination to derive the main contents. By analysing the authorships
4
of those papers (Figures 1 and 2) it can be seen how the interest is roughly equally
distributed between industry and academia, and how the applications of Six Sigma in
the service sector are becoming more prevalent. After this step, 76 publications were
identified as being available and suitable for the present work and an analysis was
conducted on these particular papers because of the higher level of detail offered
compared to the rest of the papers. The results of these search help provide the
following series of key findings.
Figure 1 – Number of articles and their authorship
Figure 2 – Percentage of articles focused on manufacturing and services
5
3.
GENERATION OF KEY FINDINGS
The literature review established seven key findings (topics on which the views of the
authors converged) and two principal issues (topics on which authors had differing
views). This section presents each of them.
3.1
Definition of Six Sigma
From the various definitions found in the reviewed publications, it was possible to
identify at least four streams of thought of Six Sigma.
The first stream defines Six Sigma as a set of statistical tools adopted within the quality
management to construct a framework for process improvement (Goh and Xie, 2004;
McAdam and Evans, 2004). The objective is to enhance the Six Sigma level of
performance measures referred to as the Critical to Quality (CTQ) which reflects the
customer requirements through a group of tools for the analysis of the data. Statistical
tools identify the main quality indicator which is the Parts per Million (PPM) of nonconforming products (Mitra, 2004). Achieving a Six Sigma level means having a
process that generates outputs with less than 3.4 defective parts per million (Coleman,
2008; Anand et al, 2007). Here, Six Sigma is recognised as a problem solving method
that uses quality and statistical tools for basic process improvements but not
necessarily a comprehensive management system.
The second stream defines Six Sigma as an operational philosophy of management
which can be shared beneficially by customers, shareholders, employees and suppliers
(Chakrabarty and Tan, 2007). Thanks to its flexibility, Six Sigma application is not
limited only to manufacturing but can be extended to the whole supply chain which
include the provision of services. It is, according to Yang et al (2007), useful to enforce
a more disciplined approach towards supply chain projects to define and execute them
more rigorously. Six Sigma is also defined as a multifaceted, customer oriented,
6
structured, systematic, proactive and quantitative philosophical approach for business
improvement to increase quality, speed up the deliveries and reduce costs (Mahanti
and Antony, 2005).
The third stream defines Six Sigma as a business culture. This stream argues that the
success of Six Sigma does not rely only on statistical tools and techniques but also on
the commitment of the top management to guarantee the involvement of the
employees in the organisation. Markarian (2004) considers Six Sigma as a rigorous top
down methodology which demands detailed analysis, fact based decisions and a
control plan to ensure ongoing quality control of a process. This organisational aspect
is also shown in the work of Pheng and Hui (2004), who define Six Sigma as a ‘cultural
and belief’ system which guides the organisation in repositioning itself towards world
class business performance by enhancing factual decision making. Similar definition is
given by Schroeder et al (2008) who consider Six Sigma as an organised structure
using process improvement specialists with the aim of achieving strategic objectives.
The fourth definition refers Six Sigma to as an analysis methodology that uses the
scientific methods. Banuelas and Antony (2004) and Thawani (2004) consider it as a
well structured continuous improvement methodology to reduce process variability and
remove waste within the business processes. Black and Revere (2006) support this by
claiming Six Sigma as a popular and widely used quality improvement methodology.
Kumar et al (2007) argue that Six Sigma ia an extension to quality improvement
initiatives such as the Total Quality Management (TQM) because of the similarities
between the Six Sigma method of Design, Measure, Analyse, Improve, Control
(DMAIC) and the Deming’s PDCA (Plan, Do, Check and Act). Using the DMAIC
method sequentially can help integrate human aspects (culture change, training,
customer focus) and process aspects (process stability and capability, variation
reduction) within the Six Sigma implementation (Antony et al, 2005).
7
Finding 1: Four interpretations of Six Sigma have been identified in the literature as a
set of statistical tools, an operational philosophy of management, a
business culture and an analysis methodology that uses the scientific
methods, although the streams are not mutually exclusive but instead,
overlapping.
3.2
Six Sigma implementation
Al-Mishari & Suliman (2008) suggest three possible ‘on-ramps’ or approaches an
organisation can take to implement Six Sigma. The first is through a business
transformation approach where an organisation undergoes complete change to convert
its traditional method of working in order to regain lost customers or to overcome the
heavy losses. The second is the strategic improvement approach limited to one or two
critical business needs focusing on major opportunities and weaknesses. The third is a
problem-solving approach which focuses only on persistent problems.
In this respect, many of the publications suggest the Design, Measure, Analyse,
Improve, Control (DMAIC) and the Design for Six Sigma (DFSS) methods as the two
most common methodologies to implement Six Sigma, although according to Edgeman
and Dugan (2008), the main objectives of the two techniques are quite different.
While DMAIC is a problem solving method which aims at process improvement, DFSS
is defined by Watson and DeYong (2010) as “a process to define, design and deliver
innovative products provide competitively attractive value to customers in a manner
that achieves the critical-to-quality characteristics for all the significant functions”. It is
therefore clear from this definition that DFSS is used in the context of new product
development that focuses on quality from the very beginning (Edgeman and Dugan,
2008). To this end, Mader (2006) believed that companies with strong market growth
and competitive position will be better-off with DFSS (focusing on product development
8
and innovation), whereas for companies with stagnant market or relatively less
competitive, DMAIC is generally a more favourable choice focusing on cost reduction,
retrenchment or divestiture.
Deploying the two approaches in different parts of the business simultaneously is
possible, even if most of the publications reviewed presented the case studies based
on either of them. As a general trend, many organisations have now extended DMAIC
to include DFSS (Mader, 2006). Possible reason is that many companies typically train
their employees in DMAIC first then expand it to DFSS which is tailored to the context
of new product and/or service development. In this respect, Banuelas and Antony
(2004) stated that in order to achieve the Six Sigma figure of 3.4 parts per million of
defects is to redesign products, key processes and services by means of DFSS. This
argument is, however, debatable as no literature clearly accepts or rejects this
hypothesis. Nonetheless, Edgeman and Dugan (2008) argue that both DMAIC and
DFSS are firmly rooted in the scientific method and are in many ways analogous to the
familiar approaches used either by the hypothesis testing or the iterative experimental
design.
The literature further shows that there are several variations for DMAIC (even if it
remains the most commonly adopted methodology) such as P-DMAIC (ProjectDMAIC), E-DMAIC (Enterprise-DMAIC) and DMAICR (DMAIC Report). The differences
are mostly in terms of the number and type of phases, rather than the tools used.
DMAICR, for instance, adds the final step of “Reporting the benefits of the reengineered process” into DMAIC (Senapati, 2004). Numerous variations of DFSS also
exist, for example DMADV (Define Measure Analyse Design Verify), DCOV (Design
Characterise Optimise Verify), IDOV (Identify Design Optimise Validate), ICOV (Identify
Characterise Optimize Verify) and DMADV (Define Measure Analyse Design Verify),
but in this case, there are no significant differences amongst them. The selection of the
9
methodology, in the end, depends on the specific requirements (Chakrabarty and Tan,
2007) and some companies implement Six Sigma not only at the project level but also
at the enterprise level (Ward et al, 2008). In these instances, either P-DMAIC or EDMAIC approach is generally used (Breyfogle III, 2008). Watson and DeYong (2010)
provide a comprehensive chronological alternative approaches to DFSS.
Finding 2: Depending on the purpose, there are two principal methodologies in which
Six Sigma can be implemented: DMAIC and DFSS. DMAIC is generally
used for process improvement and DFSS for new development of product
and services. Literature presents many variations of both.
3.3
Tools and techniques of Six Sigma
Many tools and techniques that can be applied to Six Sigma projects are available both
in the literature and public domain, e.g. Halliday (2005). Although most of these tools
are already well known and applied in other contexts, Six Sigma provides a customer
focused, well defined methodology supported by a clear set of comprehensive tools for
process improvement (van Iwaarden et al, 2008). Basic tools of DMAIC, typically used
at the Yellow-Belt level of competence include flowcharts, check sheets, Pareto
diagrams, cause/effect diagrams, scatter diagrams, histograms and Statistical Process
Control (Ferrin et al, 2005). More advanced tools such as regression analysis (e.g. with
indicator variables, curvilinear regression and logistic regression), hypothesis testing,
control charts and Design of Experiments typically feature at the Black-Belt level. This
also means Six Sigma may be viewed as a combination of existing tools and
techniques available well before Motorola developed this approach (van Iwaarden et al,
2008).
Tools are also available in various forms such as models, analysis templates and
procedures (de Koning and de Mast, 2006) and it is this wealth of techniques that
10
complicates the process, making the need of a robust set of what are essential
improvement tools to be used within the DMAIC process more obvious (Brady and
Allen, 2006). One important aspect to consider when embarking any Six Sigma project
is that tools will have to adapt and develop as the project matures. Often, simple tools
are enough to reduce the defects of a complex manufacturing system in the initial
stages (Raja, 2006).
Even though tools and techniques vary, it is essential to apply the right tool in the right
situation in order to achieve successful results. This perhaps justifies why it is a
common practice in the literature to catalogue the main tools within the five phases of
the DMAIC approach. However, there is an absence of standardised decision
procedures to choose the most appropriate tools in a specific context (Hagemeyer et
al., 2006; Kumar et al., 2008a; Williams, 2009; de Koning et al., 2008). Likewise, as put
forward by Brady and Allen (2006), finding literature that provides methods for specific
projects and the associated financial results is often difficult because of the
confidentiality reasons.
Over the years, companies have included numerous tools into the Six Sigma approach
to make them more effective and to eliminate possible gaps after its application. Such
toolsets include statistical and analytical tools both from industrial engineering and
operations research fields (Bunce et al, 2008). In this instance, these tools enrich the
practical and industrial approach with a stronger theoretical basis to achieve a better
equipment and resources utilisation (Maciel Junior et al, 2005).
The tools within the DFSS methodology are usually different from those of the DMAIC.
Chakrabarty and Tan (2007) claim that DFSS typically includes innovation tools such
as the theory of creative problem solving and axiomatic design which DMAIC does not,
although it could.
11
One notable observation during the review was the use of simulation techniques within
the ‘Improve’ phase. Although not part of the keyword search, the use of simulation is
commonly referenced in the papers but does not consistently appear in the tool
categorisation lists. Simulation is one of the tools deserving special mention as an
emerging technique that can play an important role in Six Sigma initiative today and is
considered by some authors, for example McCarthy and Stauffer (2001), to be “vital to
the long-term success of Six Sigma projects”. The evolution of computer hardware has
enabled the use of powerful simulation packages for the Analyse and Improve stages,
as it allows significant savings in the Design of Experiments phase by testing solutions
before implementation (Gladwin, 2003). Simulation has been very successful on its
own for the past twenty years but this tool was not seen as complementary to Six
Sigma and only few articles addressed the combination of such tool and methodology.
This is no longer the case today, and although still few, some authors such as
McCarthy and Stauffer (2001) state in their text that Six Sigma has already delivered
significant results without the benefit of simulation but agree that simulation could make
Six Sigma even more successful in the coming years.
Finding 3: The literature provides a wealth variety of tools and techniques which are
often classified within the DMAIC approach but with little detail on specific
examples of their applications. Basic tools are often sufficient for the initial
improvements of most processes but the simulation techniques open up a
new and promising avenue to enhance the merits already achieved by Six
Sigma.
Issue 1:
The variety of tools available sometimes causes confusion as to which
tools work best for specific business requirements. Existing literature also
categorises the Six Sigma tools based under DMAIC, however, alternative
12
approaches such as DFSS, DCOV or DMADV lack this classification of
tools.
3.4
Benefits of Six Sigma
Reduced costs, reduced project time, improved results and improved data integrity are
some of the benefits of Six Sigma suggested by Ferrin et al (2005). In addition, the
literature tends to analyse the techniques used to optimise the process performance.
The approach taken in many cases, e.g. by Lin et al (2008) and Antony et al (2005a), is
to give the solutions and the methods built by Six Sigma to achieve sensible
improvements, providing a learning process for managers in order to take a wide view
of the system and change effectively the business (Thawesaengskulthai and Tannock,
2008). There are many benefits that can be derived from the adoption of Six Sigma. It
could enhance product development cycles and process design, shorting product lead
times by reducing the cycle time of the overall manufacturing process. Six Sigma can
be used to find and eliminate the root causes of the problem, so reducing the variability
in the process in order to prevent defects.
There are also organisational implications. Indeed Six Sigma methodologies provide
guidelines which could help the workers understand how to carry out the job and train
them to solve potential problems. As a consequence, they become more aware of the
production process thereby improving their morale and reducing the human-related
defects (Hong et al, 2007). With respect to the role of Six Sigma in reducing the
defects, it has been demonstrated in several studies that the defect rate per unit (DPU)
is reduced after its implementation in manufacturing systems (Kumar et al, 2006).
The adoption of Six Sigma has improved both the efficiency of the line and production
capability, including minimising waste such as reduced need for inspection, removed
useless components and excessive movements and decreased time for repair (Oke,
13
2007). For this reason, Six Sigma can be used to build predictive models based on
experiences gathered from earlier uncorrected measures to ensure a continuous
improvement of the process (Johnston et al, 2008). In recent years, knowledge
management has contributed to facilitate the implementation of Six Sigma and has
emerged as a source of competitive advantage within the businesses (Gowen III et al,
2008). Six Sigma is also recognised as a strategy that drives the cultural change to
improve profitability of the company increasing the benefits from savings generated
when the defect is detected at a very early stage (Antony et al, 2005a). However, van
Iwaarden et al (2008) state that the approach to Six Sigma varies between
organisations because they integrate different techniques according to their needs, so
there might be disagreement regarding the benefits as they depend on the industry and
even the country where Six Sigma is applied.
Six Sigma also helps improve the relationships outside and within the organisation
(Kumar et al, 2006). It can strengthen the customer loyalty by satisfying their needs
and expectations and it works as a direct link to company’s management which helps
establish a common language from the board to the shop floor.
Finding 4: Six Sigma has many benefits and, unsurprisingly, the most frequently
cited are the reduction and prevention of defects which affect the quality
of both products and processes.
3.5
Six Sigma Adoption
Over time, Six Sigma has developed and undergone significant changes. It initially
applied in the manufacturing sector but has now spanned over service and financial
sectors (Aghili, 2009). Antony (2007) grouped these changes into three generations.
The first generation of Six Sigma (1987-1994) was focused on reduction of defects and
saw success with Motorola. The second generation (1994-2000) was concentrated on
14
cost reduction and was adopted by companies such as General Electric, Du Pont and
Honeywell. The third generation (2000 onwards) is oriented to creating value for the
customers and the enterprise itself, and finds its application within companies like
Posco and Samsung. This is more oriented to service and commercial business
processes including transactional systems quality, which takes into account delivery
times, customer waiting time to receive services, inventory service levels, etc.
Although the application of Six Sigma in service sectors is growing, the majority of the
publications reviewed discuss the implementation and the problems encountered within
the manufacturing sectors. Possible explanation of this is, according to Hensley &
Dobie (2005), is because the service sector is dealing with intangible entities such as
customer service, i.e. providing the assistance necessary to establish good
relationships with them and aiming at an efficient communication to meet their
expectations, where the success is more difficult to quantify. On the contrary, in the
manufacturing sectors where an automatic data collection is used, for example in
assembly lines, measuring the impact of the quality control programme is much easier
to do. Furthermore, large organisations tend to initially introduced Six Sigma in their
manufacturing facilities. Only after enhancing their knowledge about the tools and
techniques to adopt, they gradually spread it to the service operations.
Literature also shows there is a different level of interest shown in the Six Sigma
adoption not only in terms of type of operations (manufacturing or service) but also in
terms of company size. In particular, multinational companies are often reported to
have reaped the full benefits of Six Sigma. However, because of the project-based
approach in DMAIC, Small and Medium Enterprises (SME) should also benefit from it
(Antony et al, 2005a).
15
It also emerged that many large companies, e.g. Xerox, Fidelity Investments, integrate
Six Sigma with other techniques such as Lean (Ranch, 2006; Hensley & Dobie, 2005),
Quality Management System (Morgan & Brennig, 2006), and Kaizen/Continuous
Improvement, e.g. Caterpillar (Haikonen et al, 2004). This shows how the availability of
resources can play an important role in successful adoption of Six Sigma that can be
powerfully integrated other techniques to get optimum benefits out of it (Nonthaleerak,
& Hendry, 2008). Furthermore, Pantano et al (2006) proposed the application of Six
Sigma in a cluster of small companies so that they can share their resources and
achieve the needed level of inputs as possible solution to overcome the difficulties
found in the SMEs.
Finding 5: Six Sigma is very much in use within the manufacturing sector but is
growing in the service sector. More research is required to understand Six
Sigma adoption within the SMEs.
3.6
Enablers of Six Sigma
There is little evidence in the literature to highlight linkage between Six Sigma and
organisation
culture
despite
their
combinatorial
significance
in
present
day
manufacturing or service organisations (Davison & Shagana, 2007). However, sound
success of it is likely in the event of continuous refinement of culture in organisation
(Kwak & Anbari, 2006). Lee-Mortimer (2007) observed a company wide training to
promote Six Sigma as a relevant tactic to combat initial reluctance towards cultural
change. He also suggested that reducing the levels in organisational structure may
speed up the adoption of Six Sigma culture. Welch (2005) believed that it is necessary
to make Six Sigma a leadership tool for transformation that should permeate into all
levels of businesses. The effort required is to change the approach to the
implementation of Six Sigma projects from merely using a set of tools to the creation of
a culture that should be deeply embedded in every employee (Antony, 2004).
16
Involvement and commitment from top management is the prime enabler in increasing
level of a Six Sigma programme implementation (Chung et al, 2008). Furthermore, in
order to facilitate the communication within the organisation and to support the
implementation process, Information Technology and state-of-the-art Information
Systems infrastructure are fundamental. They continually enable integration of complex
tasks in obtaining feasible quality improvement solutions in a short time frame (Hsieh et
al, 2007). Thanks to an organised and systematic approach, the role of Six Sigma as a
‘managerial tool’ for improving quality and productivity can be extended to a ‘systemic
tool’ for quality and process control (Han et al, 2008).
It is important to note that Six Sigma does not provide a quick and easy solution to all
types of manufacturing problems and the environment in which it is introduced (LeeMortimer, 2006). Furthermore, he also suggested that small and medium enterprises
should gradually adopt Six Sigma as it will help to evenly stretch their resources and
capabilities to get the most out of them. Regardless the size of the company, McAdam
& Laffert (2004) agree that empowerment of people, involvement, motivation, effective
communication, reward and recognition system play a critical role in the success of Six
Sigma implementation. This can be achievable through a transformational leadership,
which is helpful in motivating employees to attain transcendental goals rather than their
own short term interests (Montes & Molina, 2006). This means adapting the strategy
definition, although the above mentioned authors suggest there are few papers in
literature regarding the integration of Six Sigma perspective and practices into the
strategy formulation process even if it inherently is a concern for a successful Six
Sigma initiative.
The linkage between Six Sigma and organisation culture needs to be understood.
Successfully enabling these factors, nurturing quality culture amongst workforce and
taking concern for the issues expressed above, will shape improvements and increase
17
productivity, thereby making Six Sigma more pervasive and indispensable in both
manufacturing and service organisations.
Finding 6: Committed leadership of top management and fully fledged training are
crucial to the success of Six Sigma implementation. Blending IT expertise
with Six Sigma to propel improvements and plausible significant savings
are also important. Human resource functions need good harmonisation
with Six Sigma approach leading to a general involvement within the
organisation.
3.7
Links to other disciplines
The pressure to remain competitive by providing a high quality product to satisfy the
customer requirements has led to a comprehensive analysis of quality, speed and
agility within and outside the company boundaries. Existing literature explicitly identifies
higher customer satisfaction as a significant benefit from the integration of Lean and
Six Sigma concepts (Thomas et al, 2009; Teresko, 2008) but it does not show
consensus about how to create such integration. The majority of the papers present the
DMAIC approach as a roadmap and suggests to call on Lean tools when appropriate to
carry out the two kind of practices in parallel (Thomas et al, 2009; Proudlove et al,
2008; de Koning et al, 2008). In other cases, some authors identified the absence of a
systemic methodology to merge the two concepts resulting in the implementation of
Lean and Six Sigma in sequence (Näslund, 2008; Shah et al, 2008). What is evident
and common, however, is that the amalgamation of the two complementary techniques
has brought significant benefits to the company performance.
Six Sigma has also been applied by Kumar et al (2008b) in the context of supply chain
design. They used DMAIC approach to analyse mitigation of container security risk.
Thanks to the Six Sigma process approach orientation, the supply chain can be
18
monitored and improved using the Six Sigma metrics. Those metrics create a common
denominator (Defect per Unit) for the analysis of all the systems on the same scale,
from products to processes (Dasgupta, 2003; Kumar et al, 2008b).
As previously stated, there is a debate among the authors about the originality of Six
Sigma. Six Sigma offers a common metric to align and evaluate the performance of all
the functions within the organisation and gives a methodology to translate the TQM
philosophy into practices. Six Sigma also keeps the main principles of TQM such as
customer focus (identified as Critical To Quality in the “Define” phase within DMAIC),
employee involvement (Green belts and Black belts team leaders who lead selfdirected work teams are empowered to make changes), continuous improvement (the
“Control” phase within DMAIC), enlightened leadership (represented by the champion
in Six Sigma team) and fact-based decision making (Six Sigma is visibly data oriented)
(Green, 2006; Black and Revere, 2006). There are many benefits applying both Six
Sigma and TQM in complementary because in fact Six Sigma is the extension to TQM,
in which the TQM philosophy is at the core of Six Sigma. As Andersson et al (2006) put
forward, Six Sigma is a structured methodology within the more general framework of
TQM and it provides a series of concepts and tools that support the overall principles
and aims of TQM.
The literature also demonstrates the link between Six Sigma and Kaizen (continuous
improvement) and defines a structure to improve the company performance using the
DMAIC steps and making Six Sigma an ongoing effort (Savolainen & Haikonen, 2007;
Ehie & Sheu, 2005; Murugappan & Keeni, 2003). In fact, Kaizen tools are major tools in
Six Sigma Green belt project.
Not widely documented, however, is the relationship between Six Sigma and the
Process Management. Hammer (2002) recognises the standing-alone as major limit of
19
Six Sigma and states that it should be more aligned with the enterprise and part of the
Process Management in order to identify when the Six Sigma approach is not enough
and a radical re-engineering of the process in needed. Equally rarely reported is the
link between Six Sigma and sustainability. The first authors to study the topic of
sustainability in the production phase were Miron and Skarke (1981). The reason for
this was possibly because the concept of sustainability within Six Sigma is implicitly
contained within the Control phase of the DMAIC. Further research might be needed to
identify possible benefits driven by Six Sigma in this promising field.
Finding 7: Six Sigma is a complementary approach to Lean, an extension to TQM
and is suitable to many applications thanks to its process-oriented view,
brought together in a structured methodology to increase the system
performance and to ensure a continuous improvement culture.
Issue 2:
The key areas of connection between Six Sigma and sustainability as well
as the integration between Six Sigma and the Enterprise Process
Management remain relatively unexplored.
4.
CONCLUSIONS
In recent years there has been a lot of interest in the application of Six Sigma
principles. Numerous papers have been presented on this subject substantiating the
importance of adopting Six Sigma to improve process performance. This research is
carried out to identify the latest trends, various approaches, tools and techniques,
benefits and combinations of Six Sigma with other concepts by carrying out a
systematic, thematic literature review.
Although there is a considerable amount of publication about Six Sigma and therefore
a lot of different points of view, it is possible to identify four interpretations of Six Sigma:
a set of statistical tools, an operational philosophy of management, a business culture
20
and an analysis methodology that uses the scientific methods, although the streams
are not mutually exclusive but instead, overlapping. The main goals of Six Sigma,
however, remain unchanged, i.e. improving efficiency, profitability and capability in the
process.
There are a large number of tools and techniques within Six Sigma. The variety of
tools, however, often causes confusion as to which tools work best for what
circumstance of the businesses. A systematic way to guide the selection of these of
tools is desirable. Existing literature also traditionally categorises these Six Sigma tools
under DMAIC but classification of tools under other alternative approaches such as
DFSS, DCOV or DMADV is lacking. Possible explanation of this is that all these DFSS
tools are custom-selected for a particular R&D process, industry and use, so a fixed
formulation is not possible beyond a broad categorisation (Watson, 2005).
Another issue, as mentioned before, is to clarify the use of the statistical tools and to
understand how the simulation can help in the proactive analysis of the systems.
Simulation techniques have been identified as one of the promising ones.
The main enabler for Six Sigma implementation is the top management commitment
that can promote an effective companywide training to let all the employees be
involved in the project.
The initial methodology of Six Sigma was focused on process improvement and
accordingly DMAIC approach was universally adopted, but as time progressed, the
need of implementing Six Sigma at design stage of product (or process) was felt crucial
and hence the concept of Design for Six Sigma (DFSS) was developed. Several
slightly different variations of the aforementioned approaches are available in the
literature.
21
Despite the increased number of papers discussing the adoption of Six Sigma in the
service sector in the last few years, the detailed implementation in Small and Medium
Enterprises (SMEs) was not widely reported in the academic literature, with the
exception of e.g. Antony et al (2005a) and Nonthaleerak & Hendry (2008).
The literature also supports the view that by adopting Six Sigma the variability in a
process will be reduced. In addition to the direct savings which are achieved by
improved quality and reduced scrap, the organisation can also be benefited from the
indirect savings such as in lower rework cost, minimum product recalls, low warranty
liabilities, higher customer satisfaction and brand loyalty.
These findings support the view that despite Six Sigma is considered as a fully
developed methodology, further research is needed to establish a more systematic
approach to help companies, especially SMEs, embark on Six Sigma projects.
Although the general approach is quite well known and largely applied in large
manufacturing organisations, further work is required to investigate implementation of
Six Sigma in the service sector as well as in smaller companies.
This paper has extended the work of Brady and Allen (2006). The findings and issues
have provided new insights to take Six Sigma to the next level. This work also
contributes the theoretical platform enabling deeper analyses to be carried out on the
highlighted fields. As Six Sigma continues to develop and evolve, this type of work
should also carry on.
As for the future work, the key findings and issues arising from the evidence gained in
the literature need to be further validated, in particular, confirmation of the possible link
between Six Sigma and other concepts such as sustainability and the emerging
business model of Product Service Systems (PSS) (Baines et al, 2009). How Six
Sigma can be used to facilitate manufacturing organisations to shift from selling
22
product-only to selling integrated product and services, for example, is yet to be
explored. The authors are mindful that Six Sigma principles and theories were not
developed solely in the academic journals, but instead progressed out of the
practitioners. The role of academics in this respect is to underpin these developments
with a theoretical basis.
5.
REFERENCES
Aghili, S. (2009), “A Six Sigma Approach to Internal Audits”, Strategic Finance, vol. 90,
no. 8, pp. 38-43
Al-Mishari, S.T. and Suliman, S. (2008), “Integrating Six-Sigma with other reliability
improvement methods in equipment reliability and maintenance applications”,
Journal of Quality in Maintenance Engineering, vol. 14, no. 1, pp. 59-70
Anand, R. B., Shukla, S. K., Ghorpade, A., Tiwari, M. K. and Shankar, R. (2007), “Six
Sigma-based approach to optimise deep drawing operation variables”,
International Journal of Production Research, vol.45, no. 10, pp. 2365-2385
Andersson, R. and Eriksson, H. and Torstensson, H. (2006), “Similarities and
differences between TQM, six sigma and lean”, TQM Magazine, vol. 18, no. 3, pp.
282-296
Antony, J. (2004), "Some pros and cons of six sigma: an academic perspective", TQM
Magazine, vol. 16, no. 4, pp. 303-306
Antony, J. (2007), “Is six sigma a management fad or fact?”, Assembly Automation, vol.
27, no. 1, pp. 17-19
Antony, J., Kumar, M. and Madu, C. N. (2005a), ”Six Sigma in small and medium sized
UK manufacturing enterprises”, International Journal of Quality and Reliability
Management, vol. 22, no. 8, pp. 860-874
Antony, J., Kumar, M. and Tiwari, M. K. (2005b), “An application of Six Sigma
methodology to reduce the engine-overheating problem in an automotive
company”, Proceedings of the Institution of Mechanical Engineers, Part B: Journal
of Engineering Manufacture, vol. 219, no. 8, pp. 633-646
Arnheiter, E.D. and Maleyeff, J. 2005), “The integration of lean management and Six
Sigma”, The TQM Magazine, vol. 17, no. 1, pp. 5-18
23
Baines, T.S., Lightfoot, H.W, Benedettini, O. and Kay, J.M. (2009), “The servitization of
manufacturing: a review of literature and reflection on future challenges”, Journal
of Manufacturing Technology Management, vol. 20, no. 5, pp. 547-567
Banuelas, R. and Antony, J. (2004), “Six Sigma or Design for Six Sigma”, TQM
Magazine, vol. 16, no. 4, pp.250-263
Black, K. and Revere, L. (2006), “Six Sigma arises from the ashes of TQM with a twist”,
International Journal of Health Care Quality Assurance, vol. 19, no. 3, pp. 259-266
Brady, J.E. and Allen, T.T. (2006), "Six Sigma Literature: A Review and Agenda for
Future Research", Quality and Reliability Engineering International, vol. 22, pp.
335-367
Breyfogle III, F. W. (2008), “Better Fostering Innovation: 9 steps that improve lean six
sigma”, Business Performance Management Magazine, vol. 6, no. 3, pp. 16-20
Bunce, M. M., Wang, L. and Bidanda, B. (2008), “Leveraging Six Sigma with industrial
engineering tools ins crateless retort production”, International Journal of
Production Research, vol. 46, no. 23, pp. 6701-6719
Chakrabarty, A. and Tan, K. C. (2007), “The current state of Six Sigma application in
services”, Managing Service Quality, vol. 17, no. 2, pp.194-208
Chung, Y.C., Hsu, Y.W., and Tsai, C.H. (2008), "An empirical study on the correlation
between Critical DFSS success factors, DFSS implementation activity levels and
business competitive advantages in Taiwan's high-tech manufacturers.", Total
Quality Management, vol. 19, no. 6, pp. 595-607
Coleman, S. (2008), “Six Sigma: An opportunity for statistics and for statisticians”,
Significance, vol. 5, issue 2, pp. 94-96
Dasgupta, T. (2003), “Using the six-sigma metric to measure and improve the
performance of a supply chain”, Total Quality Management and Business
Excellence, vol. 14, no. 3, pp. 355-366
Davison, L. and Shaghana, K.A (2007), "The Link between Six Sigma and Quality
Culture: An Empirical Study", Total Quality Management, vol. 18, no. 3, pp. 249265
de Koning, H. and de Mast, J. (2006), “A rational reconstruction of Six-Sigma’s
breakthrough cookbook”, International Journal of Quality & Reliability
Management, vol. 23, no. 7, pp.766-787
24
de Koning, H., de Mast, J., Does, R.J.M.M., Vermaat, T. and Simons, S. (2008),
“Generic Lean Six Sigma Project Definitions in Financial Services”, Quality
Management Journal, vol. 15, no. 4, pp. 32-45
Edgeman, R. L. and Dugan, J. P. (2008), “Six Sigma from products to pollution to
people”, Total Quality Management, vol. 19, no. 1-2, pp. 1-9
Ehie, I. and Sheu, C. (2005), “Integrating six sigma and theory of constraints for
continuous improvement: A case study”, Journal of Manufacturing Technology
Management, vol. 16, no. 5, pp. 542-553
Ferrin, D., Miller, M. and Muthler, D. (2005), “Lean sigma and simulation, so what’s the
correlation? V2”, in: Proceedings of the 2005 Winter Simulation Conference, 4-7
December 2005, Orlando, Florida, pp. 2011-2015
Furterer, S. and Elshennawy, A.K. (2005) “Implementation of TQM and lean Six Sigma
tools in local government: a framework and a case study”, Total Quality
Management & Business Excellence, vol. 16, issue 10, pp. 1179 - 1191
Gladwin, B. (2003), “Six Sigma & Simulation”, Promodel White Paper,
http://www.hearne.com.au/attachments/White%20Paper_Simulation%20Enhances
%20Six%20Sigma.pdf, last accessed 2 June 2010
Goh, T. N. and Xie, M. (2004), “Improving on the Six Sigma paradigm”, TQM
magazine, vol. 16, no. 4, pp. 235-240
Gowen III, C. R., Stock, G. N. And McFadden, K. L. (2008), “Simultaneous
implementation of Six Sigma and knowledge management in hospitals”,
International Journal of Production Research, vol. 46, no. 23, pp. 6781-6795
Green, F. B. (2006), “Six-sigma and the revival of TQM”, Total Quality Management
and Business Excellence, vol. 17, no. 10, pp. 1281-1286
Hagemeyer, C., Gershenson, J. K. and Johnson, D. M. (2006), “Classification and
application of problem solving quality tools”, TQM Magazine, vol. 18, no. 5, pp.
455-483
Haikonen, A., Savolainen, T. and Järvinen, P. (2004), “Exploring Six Sigma and CI
capability development: Preliminary case study findings on management role”,
Journal of Manufacturing Technology Management, vol. 15, no. 4, pp. 369-378
Halliday, S. (2005), “Application of Tools in Six Sigma”,
http://www.wdpc.co.uk/articles/tools6sig.pdf, last accessed 25 November 2009.
25
Hammer, M. (2002), “Process management and the future of six sigma”, MIT Sloan
Management Review, vol. 43, no. 2, pp. 26-32
Han, H.S., Chae, M.J., Im, K.S. and Ryu, H.D. (2008), "Six Sigma-Based Approach to
Improve Performance in Construction Operations", Journal of Management in
Engineering, vol. 24, no. 1, pp. 21-31
Hensley, R. L. and Dobie, K. (2005), “Assessing readiness for Six Sigma in a service
setting”, Managing Service Quality, vol. 15, no. 1, pp. 82-101
Hong, K., Nagarajah, R., Iovenitti, P., and Dunn, M. (2007), “A Sociotechnical
Approach to Achieve Zero Defect Manufacturing of Complex Manual Assemblies”,
Human Factors and Ergonomics in Manufacturing, vol. 17, no. 2, pp. 137–148
Hsieh, C.T., Lin, B. and Manduca, B. (2007), "Information Technology and Six Sigma
Implementation", Journal of Computer Information Systems, vol. 47, no. 4, pp. 1-10
Johnston, A. B., Maguire, L. P., McGinnity, T. M. (2008), “Disentangling causal
relationships of a manufacturing process using genetic algorithms and six-sigma
techniques”, International Journal of Production Research, vol.46, no. 22, pp.
6251-6268
Kumar, M., Antony, J., Antony, F. J. and Madu, C. N. (2006), “Winning Customer
Loyalty in an Automotive Company through Six Sigma: a Case Study”, Quality
Reliability Engineering International, vol. 23, pp. 849–866
Kumar, M., Antony, J., Madu, C. N., Montgomery, D. C., and Park, S. H. (2008),
“Common myths of Six Sigma demystified”, International Journal of Quality and
Reliability Management, vol. 25, no. 8, pp. 878-895
Kumar, S., Jensen, H. and Menge, H. (2008), “Analyzing Mitigation of Container
Security Risk Using Six Sigma DMAIC Approach in Supply Chain Design”,
Transportation Journal, vol. 47, no. 2, pp. 54-67
Kumar, U. D., Nowicki, D., Ramirez-Marquez, J. R. and Verma, D. (2007), “On the
optimal selection of process alternatives in a Six Sigma implementation”,
International Journal of Production Economics, no. 111, pp. 456-467
Kumar, S. and Bauer, K.F. (2010) “Exploring the Use of Lean Thinking and Six Sigma
in Public Housing Authorities”, Quality Management Journal, vol. 17, no. 1
Kwak, Y.H. and Anbari, F.T. (2006), "Benefits, Obstacles and future of Six Sigma
approach", Technovation, vol. 26, no. 5-6, pp. 708-715
26
Lee-Mortimer, A. (2006), "Six Sigma: a vita improvement approach when applied to the
right problems, in the right environment", Assembly Automation, vol. 26, no. 1, pp.
10-17
Lee-Mortimer, A. (2007), "Leading UK manufacturer probes the potential of Six Sigma",
Assembly Automation, vol. 27, no. 4, pp. 302-308
Lin, L. C., Li, T. S. and Kiang, J. P. (2008), “A Continual Improvement Framework with
Integration of CMMI and Six-Sigma Model for Auto Industry”, Quality and Reliability
Engineering International, vol. 25, issue 5, pp. 551 - 569
Maciel Junior, H., Batista Turrioni, J., Cesar Rosati, A., Garcia Neto, D., Kenji Goto, F.,
Fujioka Mologni, J., Machado Fernandes, M. (2008), “Application of Design for Six
Sigma (DFSS) on an Automotive Technology Development Process”, SAE
Technical paper series
Mader, D. P (2006), “Deploying the 'D' in DFSS”, Quality Progress, vol. 39, no. 7, pp.
73-74
Mahanti, R. and Antony, J. (2005),”Confluence of Six Sigma, Simulation and Software
development”, Managerial Auditing Journal, vol. 20, no.7, pp.739-762
Markarian, J. (2004),”What is Six Sigma?”, Reinforced Plastics July-Aug 2004, pp. 4649
Mcadam, R. and Evans, A. (2004), “Challenges to Six Sigma in a high technology
mass manufacturing environments”, Total Quality Management, vol. 15, no. 5-6,
pp. 699-706
McAdam, R. and Laffert, B. (2004), "A multilevel case study critique of six sigma:
Statistical control or strategic change?", International Journal of Operations and
Production Management, vol. 24, no. 5-6, pp. 530-549
McCarthy, B. and Stauffer, R. (2001), “Enhancing six sigma through simulation with
iGrafx process for six sigma”, in: Proceedings of the 2001 Winter Simulation
Conference, vol. 2, 9-12 December 2001, Arlington, USA, p. 1241-1247
Miron, J.R. and Skarke, P. (1981), “Non-price information and price sustainability in the
Koopmanns-Beckmann problem”, Journal of Regional Science, vol.21, no.1,
pp.117-122
Mitra, A. (2004),”Six Sigma Education: a critical role for academia”, TQM magazine,
vol. 16, no. 4, pp.293-302
27
Montes, F.J.L. and Molina, L.M. (2006), "Six Sigma and Management Theory:
Processes, Content and Effectiveness", Total Quality Management, vol. 17, no. 4,
pp. 485-506
Morgan, J. and Brennig, M. J. (2006), “Six Sigma and the Future of Quality”,
Management Services, vol. 50, no. 2, pp. 46-47
Murugappan, M. and Keeny, G., (2003), “Blending CMM and Six Sigma to meet
business goals”, IEEE Software, vol. 20, no.2, pp.42-48
Näslund, D. (2008), “Lean, six sigma and lean sigma: Fads or real process
improvement methods?”, Business Process Management Journal, vol. 14, no. 3,
pp. 269-287
Nonthaleerak, P. and Hendry, L. (2008),”Exploring the Six Sigma phenomenon using
multiple case study evidence”, International Journal of Operations and Production
management, vol. 28, no. 3, pp.279-303
Oke, S. A. (2007), “Six Sigma: A literature Review”, South African Journal of Industrial
Engineering, vol. 18, no. 2, pp. 109-129
Pantano, V., Kane, P. O. and Smith, K. (2006), “Cluster-Based Six Sigma Deployment
in Small and Medium Sized Enterprises”, Management of Innovation and
Technology, vol. 2, pp. 788-792
Patel, S.C. and Zu, X. (2009), “E-government application development using the Six
Sigma approach”, Electronic Government, an International Journal, vol. 6, no. 3,
pp. 295 - 306
Pheng, L. S. and Hui, M. S. (2004), “Implementing and Applying Six Sigma in
Construction”, Journal of Construction Engineering and Management, vol. 130, no.
4, pp. 482-489
Proudlove, N. and Moxham, C. and Boaden, R. (2008), “Lessons for lean in healthcare
from using six sigma in the NHS”, Public Money and Management, vol. 28, no. 1,
pp. 27-34
Raja, A. (2006), “Simple Tools for Complex Systems”, Quality Progress, vol. 39, no. 6,
pp. 40-44
Ranch, H. (2006), “Xerox Find the Right Tool for Tracking Continuous Improvement”,
Manufacturing Business Technology, vol. 24, no. 2, pp. 42-45
28
Savolainen, T. and Haikonen, A. (2007), "Dynamics of organizational learning and
continuous improvement in six sigma implementation", TQM Magazine, vol. 19, no.
1, pp. 6-17
Schroeder, R. G., Linderman, K., Liedtke, C. and Choo, A. S. (2008),”Six Sigma:
Definition and Underlying theory”, Journal of operations management, no. 26, pp.
536-554
Sehwail, L. and DeYong, C. (2003), “Six Sigma in health care”, Leadership in Health
Services, vol. 16, no. 4, pp. 1-5
Senapati, N. R. (2004), “Quality and Reliability Corner: Six Sigma: myths and realities”,
International Journal of Quality and Reliability Management, vol. 21, no. 6/7, pp.
683-690
Shah, R. and Chandrasekaran, A. and Linderman, K. (2008), “In pursuit of
implementation patterns: The context of Lean and Six Sigma”, International
Journal of Production Research, vol. 46, no. 23, pp. 6679-6699
Teresko, J. (2008), “How to organize for lean/Six Sigma”, Industry Week, vol. 257, no.
11, pp. 38-41
Thawani, S. (2004), “Six Sigma – strategy for organizational excellence”, Total Quality
Management, vol. 15, no. 5-6, pp.655-664
Thawesaengskulthai, N. and Tannock, J.D.T. (2008), “A Decision Aid for Selecting
Improvement Methodologies”, International Journal of Production Research, vol.
46, no. 23, pp. 6721-6737
Thomas, A. and Barton, R. and Chuke-Okafor, C. (2009), “Applying lean six sigma in a
small engineering company- A model for change”, Journal of Manufacturing
Technology Management, vol. 20, no. 1, pp. 113-129
van den Heuvel, J., Does, R.J.M.M. and Verver, J.P.S. (2005), “Six Sigma in
healthcare: lessons learned from a hospital”, International Journal of Six Sigma
and Competitive Advantage, vol. 1, no. 4, pp. 380 - 388
van Iwaarden, J., van Der Wiele, T., Dale, B., Williams, R. and Bertsch, B. (2008), “The
Six Sigma improvement approach: a transnational comparison”, International
Journal of Production Research, vol. 46, no. 23, pp. 6739-6758
Ward, S.W, Poling, S.R. and Clipp, P. (2008), “Selecting Successful Six Sigma
Projects”, Quality, vol. 47, no. 10, pp. 50-51
29
Watson, G.H. (2005), “Design for Six Sigma: Innovation for Enhanced
Competitiveness”, Goal/QPC
Watson, G.H. and DeYong, C.F. (2010), “Design for Six Sigma: caveat emptor”,
International Journal of Lean Six Sigma, vol. 1, No. 1, pp. 66-84
Wei, C., Sheen, G., Tai, C. and Lee, K. (2010), “Using Six Sigma to improve
replenishment process in a direct selling company, Supply Chain Management,
vol. 15, issue 1, pp. 3-9
Welch, J. (2005), “Six Sigma Leaders”, Quality, vol. 44, no. 3, pp. 80-80
William, S. (2009), “The Lean Toolkit, Part I”, CiruiTree, vol. 22, no. 2, pp. 36
Yang, H.M., Choi, B.S., Park, H.J., Suh, M.S. and Chae, B. (2007), “Supply chain
management Six Sigma: a management innovation methodology at the Samsung
Group”, Supply Chain Management: An International Journal, vol. 12, no. 2, pp.
88-95
30
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