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Lean Six Sigma Literature: A Review and Agenda for Future Research

THESIS

Presented in Partial Fulfillment of the Requirements for the Degree Master of Science

in the Graduate School of The Ohio State University

Thomas J. Zugelder

G r a d u a t e P r o g r a m i n In t e g r a t e d S ys t e m s E n gi n e e r i n g

The Ohio State University

2012

Thesis Committee:

Theodore T. Allen Ph.D., Advisor

Clark Mount-Campbell Ph.D.

Thomas J Zugelder

2012

ABSTRACT

The purpose of this thesis is to investigate the trends in published research

concerning Lean Six Sigma and continuous improvement. We use published research in

the areas of continuous improvement, for example Lean Manufacturing, Six Sigma, Lean

Six Sigma, and Sustainability to show that this growth in popularity is spurring more

research, technical papers, and a general direction within academia and the business

community.

The six sigma literature and lean six sigma literatures have continued to grow.

Specifically, the volume of articles on lean six sigma has grown 415% by one measure in

five years. Yet, in proportion the majority of relevant articles continue to be on six sigma

alone. Relevant literatures focusing on overlaps of six sigma with other concepts such as

simulation, optimization, and sustainability also have experienced rapid growth. We

found a change in the perceptions about success factors from a previous emphasis on top

management commitment to a new emphasis on structured approaches. This development

combined with the rise of new technology intensive methods such as optimization and

simulation which are combined with lean sigma indicate to us a maturing of the literature

and the organizations that support it. Finally, by examining statistics about the document

database, we develop hypotheses about the future including those relating to

sustainability and energy conservation and lean six sigma methods.

Keywords: Lean Six Sigma, Capability Maturity Model, Sustainability

iii

Dedication

Dedicated to my wife and kids

Acknowledgements

I would like to thank my wife, Kim Zugelder, for her continued support of my studies. I

would also like to thank my adviser, Dr. Theodore Allen, for all his support including

ideas, criticism, encouragement, and guidance. Similarly, I thank would like to thank Dr.

Clark Mount-Campbell who contributed to my studies.

Vita

1993-1997 ..............................................................B.S. Mechanical Engineering, S.U.N.Y. Buffalo

Buffalo, New York

1999-2001 ...............................................................Master’s in Business Administration Fisher College of Business The Ohio State University

Columbus, Ohio

2008-present............................................................Graduate Research Integrated Systems Engineering

The Ohio State University Columbus, Ohio

Field of Study

Major Field: Integrated Systems Engineering

Table of Contents

Abstract…………………………………………………………………………….. ii

Dedication………………………………………………………………………….. iii

Acknowledgments…………………………………………………………………..iv

Vita…………………………………………………………………………………..v

List of Tables………………………………………………………………………..vii

List of Figures ……………………………………………………………………….viii

Research ……………………………………………………………………………. 1

References …........................................................................................................... 37

Appendix A ………………………………………………………………………… 41

vii

List of Tables

Table 1: Descriptors used to classify articles ………………………………………. 18

Table 2: List of Journals or Proceedings with at least one article in the study …... 43

viii

List of Figures

Figure 1: Time Series of Google Search “Lean Manufacturing” ………………………. 7

Figure 2: Time Series of Science Citation Index Databases “Lean Manufacturing” …… 8

Figure 3: Time Series of Google Search “Six Sigma” …………………………………. 10

Figure 4: Time Series of Science Citation Index Search of “Six Sigma” ……………… 11

Figure 5: Time Series of Google Search “Lean Six Sigma” …………………………… 12

Figure 6: Time Series of Science Citation Index Search of “Lean Six Sigma” ……… 13

Figure 7: % of “Lean Six Sigma” Articles Increasing Over Time Versus “Lean

Manufacturing” And “Six Sigma” …………………………………………………… 14

Figure 8: % of “Lean Six Sigma” Articles From Engineering Articles versus Business

Articles …………………………………………………………………………………. 15

Figure 9: Screen Shot of the Query Used In Google Scholar ………………………… 16

Figure 10: The Breakdown of Articles by their Authorship by Year ………………… 20

Figure 11: The % of Lean Six Sigma Articles by their Authorship …………………… 21

Figure 12: The Percentage of Articles Focused On Manufacturing Topics …………… 22

Figure 13: Percentages of Articles by Different Areas ……………………………….. 23

Figure 14: Number of Articles from Country of Origin ……………………………… 24

Figure 15: Pareto Chart of Articles by Research Approach …………………………… 25

Figure 16: Percentage of Articles That Has Specific Success Factor ………………… 26

Figure 17: Time Series of Google Search “Toyota Production System” + “Energy

Reduction + “Lean” …………………………………………………………………… 28

List of Figures continued

Figure 18: Time Series of Google Search “Lean + Life Cycle” ……………………… 29

Figure 19: Time Series of Google Search “Toyota Production System + Life Cycle” . 30

Figure 20 – Green Lean Six Sigma’s Value to Society ……………………………… 31

Figure 21: Increase of Lean Six Sigma, Simulation, and Optimization Articles over

Time ………………………………………………………………………………… 33

Figure 22 – Capability Maturity Model – Continuous Improvement ………………… 35

Figure 23 – Screen Shot of the Science Citation Index Search Screen ……………… 42

Introduction

Lean Manufacturing and Six Sigma have been continuous improvement tools that

manufacturers have been using for over 20 years. The lean manufacturing ideology

emphasizes that the main “thrust” is having all of the tools working together to create a

streamlined, high quality system that produces products at the demand of the customer

with little or no waste (Shah and Ward, 2007). Whereas Six Sigma’s foundation is in

statistical analysis and within Six Sigma, the common measurement index is defects per

million opportunities which could include anything from a component, piece of material,

or an administrative form (Brady and Allen, 2005). Six Sigma uses the very formal

DMAIC process, which breaks down a specific project into phases. Both sets of tools

have allowed companies to reduce costs and improve quality throughout their

manufacturing operations. In some organizations Lean Manufacturing and Six Sigma

have morphed into a new subset of tools under the title of Lean Six Sigma.

In this paper, we will show the trends in published papers from Lean

Manufacturing, Six Sigma, and Lean Six Sigma over the past twenty years. We are

looking to see if these continuous improvement methodologies have grown in popularity

or have faded over time. Our initial hypotheses was that research and publications in the

fields of Lean Manufacturing, Six Sigma, and Lean Six Sigma has increased over the past

twenty years however would be on the decline in more recent years. We will depict and

analyze the trends in all three subject areas within the paper.

Next, we examine more closely the research that was published specifically under

the category of Lean Six Sigma. We will break down the research articles in multiple

categories to show who and what is being published. Specifically, we will show

Authorship, Specific Industries, Research Topics or Methods, and Success Factors. The

categories used to break down the Success Factors was used initially to correspond to the

quality management practice used by Sousa and Voss and successfully used to analyze

Six Sigma literature by Brady and Allen in 2005.

The literature search analysis that we did initially around continuous improvement

and the more detailed analysis, specifically, around Lean Six Sigma, allowed us to predict

where future research in the area of continuous improvement would evolve. We looked

into the area of “green” or sustainability since it appeared to us this is a trendy subject

and we also looked at simulation and optimization because these seemed to us to be a

natural evolution in continuous improvement. We then discuss the Capability Maturity

Model and how it could be applied to continuous improvement.

Lean Manufacturing

Lean thinking originated within the Japanese automobile industry following

World War II and is principally based on the Toyota Production System (TPS). Lean is

much more than a combination of tools, methods and principles. It is the mindset of

everyone who works within the organization (Drew et.al. 2004). Lean is an integrated

system of principles, practices, tools, and techniques that are focused on reducing waste,

synchronizing work flows, and managing production flows (Koninget.al. 2006).

Lean is concentrated with the reduction of waste (“muda” in Japanese). The

understanding that if you reduce waste within the Value Stream and ultimately within the

organization, then a company’s throughput will increase. Many companies most

commonly measure throughput in units per man hour. Through the principles of lean,

such as Value Stream mapping, Single Minute Exchange of Dies [SMED], line

balancing, etc. allows an organization to increase the number of units and also reduce the

number of man hours needed to make the necessary production.

From the origination of Lean thinking at Toyota Corporation, these principles

have moved to other Japanese automotive manufactures and then to the American

automotive companies. The continued success of these companies that have

implemented lean has propelled this methodology across manufacturers of all sectors, not

just automotive. By eliminating waste, companies have increased throughput with fewer

resources thus a higher bottom line. Due to this continued success over an extended

amount of time, many academics and industry professionals have studied and researched

lean techniques, methodologies and overall mindset.

Six Sigma

There are multiple definitions of what Six Sigma is and how it is explained. It has

been written in multiple papers the need to standardize the actual definition. In Brady

and Allen’s paper (Brady and Allen, 2005), they go through some of the variations to the

definition starting with Linderman’s definition and go through the various other authors

that give their opinions on how it should be defined. Ultimately, Six Sigma’s foundation

is in statistical analysis and within Six Sigma, the common measurement index is defects

per million opportunities and can include anything from a component, piece of material,

and an administrative form (Brady and Allen, 2005). This foundation started at Motorola

in 1979 and they were able to change the mindset that improving quality costs money.

They proved that improving quality actually reduced operating costs and increased

customer satisfaction (Harry and Schroeder, 2000).

One of the main methodologies within Six Sigma is the DMAIC process, which

breaks down a specific project into phases. These phases, known as the DMAIC

methodology, are defined as Define, Measure, Analyze, Design, and Control. This

methodology guides the project team from the beginning of the project [Define] to

maintaining the results [Control]. A main concept that needs to be understood is that Six

Sigma is a performance target that applies to a single characteristic. This single

characteristic in Six Sigma methodology is known as a critical-to-quality characteristic

[CTQ] (Harry and Schoeder, 2000). This single critical-to-quality characteristic not the

total product is the goal of Six Sigma.

Six Sigma has been proven to improve both process and product quality. Due to the

success that companies such as Motorola, GE, etc. have demonstrated in their

manufacturing operations, Six Sigma methodology has moved to other areas such as

Healthcare, Service Industries, etc. This outreach to other industries has continued to

make Six Sigma a popular subject in both industry and academia. Due to this popularity,

we hypothesize that the number of published articles has increased recently over time.

Lean Six Sigma

Lean Six Sigma is becoming the leading continuous improvement technique used

by companies in various industries. From manufacturing to healthcare to IT, Lean Six

Sigma maximizes efficiency and helps control each step of the process. Lean Six Sigma

is an approach that is focused on improving quality, increasing productivity and reducing

cost in any organization. (George, 2005) This is a logical definition since Lean Six Sigma

is the combination of two different, but complimentary, approaches to continuous

improvement - Lean and Six Sigma. Previously organizations chose to use either Lean or

Six Sigma where now they have decided to use the blended techniques found in Lean Six

Sigma.

What companies have found out is that their results are much greater using the

Lean Six Sigma methodology instead of Lean or Six Sigma individually. The reason

behind this conclusion is that both Lean and Six Sigma have their benefits but also their

flaws whereas Lean Six Sigma just incorporates the best techniques, principles and

methodologies for continuous improvement.

As the IBM consulting team, led by Hans Skalle, writes that Lean Six Sigma has

also incorporated components of the systems based approach to process improvement

found in Goldratt’s Theory of Constraints. (Skalle, 2008) This statement confirms that

continuous improvement methodology, led by Lean Six Sigma, continues to change and

adapt to the challenges faced in the business environment.

In this paper, we will examine published Lean Six Sigma articles in multiple

ways. We will examine the time series analysis of the number of articles published over

time and will do a “deep dive” into specific articles published over the past six years.

Literature Review Methods

Within this paper we did various literature reviews to see the data from items that

were being published. We chose to do Literature reviews because they are good sources

of data for trends in both academia and in industry. Literature searches show where

people are concentrating their research and will give an indication of future research

trends. In our initial literature search, the intent was to see the trends over a specified

time series. In this case, we went back over the past twenty year period, 1990 through

2010, in order to capture the recent trends in the data and specifically wanted to see when

within the time series did significant changes occur. First, we started with articles that

referenced “Lean Manufacturing” within the article and then we moved on to “Six

Sigma” and finally “Lean Six Sigma”. We used both Google Scholar and the Science

Citation Index databases as our primary search databases. We used these databases

because they are commonly used are wide ranging databases.

Our initial literature search was using Google Scholar with the term “Lean

Manufacturing” used anywhere within the article. We also broke down the data to look

at Engineering and Business areas within Google Scholar. The Engineering areas

included journals from the Engineering, Computer Science and Mathematics fields and

the Business areas included journals from the areas of Business, Administration, Finance,

and Economics.

Figure 1: Time Series of Google Search “Lean Manufacturing”

As you can see from the figure, there have been a significant number of articles published

in both business and engineering journals with this subject. What is even more

interesting is the number of published articles has increased significantly overtime

particularly in the past 5 years (2006 – 2010.

We did an additional literature search on this topic using the Science Citation Index

databases. We wanted to confirm that the trends were similar in this database. We used

the search term “Lean Manufacturing” from the dates 1990 – 2010. We also restricted

the findings where the search terms only appeared in the “Topic”. A screen shot of the

search screen is shown below.

The Science Citation Index primarily shows articles that appear in technical journals.

As the graph depicts, there is still a steady increase in the number of articles, however,

nowhere near the % increase or magnitude of articles we found with the Google Scholar

search.

Figure 2: Time Series of Science Citation Index Databases “Lean Manufacturing”

Please note that the scale on Figure 2 is a magnitude smaller than the Google Scholar

chart [Figure 1]. The main reason for this is that the Science Citation Index databases are

technical in nature and do not incorporate business articles. In the Google Scholar query,

I pulled in articles from both business and engineering sources.

The results of this Science Citation Index query increases overtime we see a

similar increase in the past 5 years. This comparison to the Google Scholar database

search is which can best explained by the greater number of journals that articles were

picked from or that more Lean Manufacturing articles appeared in business journals

instead of engineering or technical journals. Both queries do show an increase in the

number of articles being published over time with the highest increases happening over

the past five years.

Next, we moved to “Six Sigma” to see if we see get a similar trend over the same

time period. We again looked at the Google Scholar database along with the Science

Citation Index databases. With the Google Scholar search, we used the search term “Six

Sigma” from 1990 – 2010 where Words Appear Anywhere in the Article. The results of

this literature search are shown in Figure 3 below.

Figure 3: Time Series of Google Search “Six Sigma”

There are similar results in this search where we see a significant number of articles

published in the past twenty years and specifically over the past five years.

We also did the “Six Sigma” search in the Science Citation Index databases. The

search criterion was from the dates 1990 – 2010 where the words appear in the “Topic.”

The results of this literature search are shown in Figure 4. The results follow the same

trend as the previous three graphs where there have been an increase number of published

articles over the past twenty months.

Figure 4: Time Series of Science Citation Index Search of “Six Sigma”

The final time series analysis we did was with the search term Lean Six Sigma. We again

started with the Google Scholar search with the term “Lean Six Sigma” from 1990 –

2010 where the words appear anywhere in the article.

Figure 5: Time Series of Google Search “Lean Six Sigma”

As depicted in Figure 5, there is a similar trend as witnessed in the other Google Scholar

searches; however, the main difference is in the number of articles published. Both with

the Lean Manufacturing and Six Sigma searches, the results, especially over the past five

years were in the magnitude of 500 to 1000 articles, if not more. In only one year, 2010

are there any articles near 500 and even in that year there were only 444 articles.

We also finished our time series literature search with the data from the Science

Citation Index databases. We used the search term “Lean Six Sigma” from the dates,

1990 – 2010, with the words appearing in the “Topic.”

Figure 6: Time Series of Science Citation Index Search of “Lean Six Sigma”

From 2005 to 2010, there are 86 articles in the Science Citation Databases. This is an

increase over the twenty year period, however, not even close to the significance of lean

manufacturing and Six Sigma.

We went back to the Google Scholar data and wanted to show the number of

articles in a different way. We wanted to show that the number of Lean Six Sigma

articles is increasing as an overall percentage when compared to Lean Manufacturing and

Six Sigma articles.

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

2005 2006 2007 2008 2009 2010

% O fA rt ic le s

Year

Lean Manufacturing Six S igma Lean Six Sigma

Figure 7: % of “Lean Six Sigma” Articles Increasing Over Time Versus “Lean

Manufacturing” And “Six Sigma”

We also want to break down the data between “engineering” articles versus

“business” articles, specifically for the Lean Six Sigma results. The graph below shows

the breakdown of “Lean Six Sigma” articles, by percentage for both Engineering and

Business articles.

Figure 8: % of “Lean Six Sigma” Articles From Engineering Articles versus

Business Articles

As stated previously, the “Engineering” articles are those that appeared in journals from

the Engineering, Computer Science and Mathematics fields whereas “Business” articles

included in journals from the areas of Business, Administration, Finance, and Economics.

The articles that appear from “Business” journals dominated the Google Scholar results

over the past 6 years. This result makes sense when one understands Lean

Manufacturing, Six Sigma, and Lean Six Sigma. These tools are continuous

improvement tools that enhance profitability and business concepts that are traditionally

studied in business schools not engineering schools. Therefore, it makes sense that most

articles are from academia and from the business schools from around the world. We

also see this when we compare the number of articles from the Science Citation Index

database, which are predominately technical journals and thus less published articles.

In our Secondary Literature Review, we felt it was necessary to a detailed

literature search of the term “Lean Six Sigma”. It was done to see what are the trends,

percentages, and detailed data was being represented in the data. In Google Scholar, we

used the Search Term: “Lean Six Sigma” in the “exact phrase” box. We used the years

from 2005 – 2010 Words Appear anywhere in the Title.

Figure 9: Screen Shot of the Query Used In Google Scholar

Figure 9 shows a screen shot from Google Scholar on how the “Lean Six Sigma” search

was done; We also used the Science Citation Index to search for articles; We searched

“Lean Six Sigma” in the Title from 2005 – 2010 From 2005 to 2010, there were 69

articles in the Science Citation Databases We verified we did not duplicate any entries

from the two databases. Then we analyzed each article and created a database so that we

could breakdown the data from these articles to see if there were any significant trends or

observations from the data.

From the database, we created the chart below that shows the list of journals and

proceedings / conference articles that provided at least one relevant article. Over 110

distinct journals and proceedings are listed. We displayed the results in Table 1 {In the

Appendix}.

The Classification Scheme

Articles were classified using 10 descriptors in Table 2. Authorship is where the

authors are representing, either academia or industry or even a combination of both

academia and industry. If the author came from academia, we listed the academic

institution in which he/she represented. The next descriptor was Industry Sector. This

descriptor is breaking down what the article is referencing whether it is manufacturing,

service or a general topic. The articles were also broken down to what format they were,

specifically, if the article was a book, journal or conference proceedings.

Descriptor Source Levels Authorship Brady and Allen; Zugelder Industrial (I), Academic (A), or

Both (IA) Academic Institution

Google Scholar and Science Citation Index

The Ohio State University, University of Bath, etc.

Industry Sector Google Scholar and Science Citation Index

Manufacturing (M), Service (S), General (G)

Book, Journal, Conference

Google Scholar and Science Citation Index

Book (B), Journal (J), or Conference (C)

Database Google Scholar and Science Citation Index

Google Scholar or Science Citation Index

Country of Origin Google Scholar and Science Citation Index

U.S.A, U.K., China, etc.

Society of Area Brady and Allen; Zugelder Manufacturing, Healthcare, ASQ, etc

Research Approach Zain et.al. (2001) Case Study (Ca), Comparative (Co), Survey (Su), Literature Review, or Theortical with

Application (TA) Success factors Brady and Allen; Zugelder All combinations of 13 possible

factors Speculative in

Nature Brady and Allen; Zugelder Yes (Y) or No (N)

Table 1: Descriptors used to classify articles

Next, the database showed what database the article came from, either Google

Scholar or Science Citation Index and what the country of origin. We then dissected the

articles society or area of concentration. Articles could be from manufacturing,

healthcare or from societies such as ASQ. The purpose of doing this was to see if there

were any significant trends or outcomes in the published articles. Research approach, for

example Case Study, Comparative, Survey, Literature Review, or Theoretical with

Application, was analyzed. The articles research approach is an interesting

categorization of the research data and this breakdown was used by Zain, Dale, and

Kehoe. (Brady, 2005)

The terminology that we used to breakdown the success factors was identical to

Brady and Allen, 2005 and they referenced Sousa and Voss because they were the first

ones to standardize the success factors to correspond to the dimensions of quality

management practice (Brady and Allen, 2005). Finally, the last descriptor that we used in

our database was Speculative in Nature. This is defined as if the author recommended or

discussed one or more practices without clarifying the conditions. Basically, if the author

proved if the practices presented in the article were defined or not. The reason we used

this methodology was that we did not want to go through an extensive statistical analysis

or even used optimization for any related justifications.

Literature Review

In this section, we present a characterization of the articles in the database by using

the descriptors that we defined in Table 2. The purpose is to show specific trends and

also overall identification, such as country of origin. We felt that is necessary to

breakdown the characteristics of the articles in the database to make sure we did not miss

any conclusions that the articles presented. Next, we looked at the articles to see if there

were any connections with Sustainability, Simulation, or Optimization. Finally, we

discuss the success factors that were presented within the data and present them in tables

so that we understand which success factors were most often cited with the literature.

Literature Trends

The first breakdown of the database articles is what we described as authorship.

Authorship is defined as the author(s) from Academia, Industry, or both. Most articles

were written by someone or the team of authors that came from academia.

Figure 10: The Breakdown of Articles by their Authorship by Year

In our initial hypothesis, we felt that most articles would come from academia versus

industry. Most academic institutions are researching on an ongoing basis and thus

publishing more. Most people in industry may be doing some type of research, but their

findings are kept internal with the company.

Figure 11: The % of Lean Six Sigma Articles by their Authorship

As you can see from the graph, the majority of the authors came from academia [61%];

however, it is a much lower percentage than we initially hypothesized.

Next, we wanted to breakout the number of articles that were focused on

manufacturing topics versus those that were concentrated around health care, other

service industries, or other areas of interest. Lean and Six Sigma have traditionally been

focused around manufacturing; however, with the success of lean and Six Sigma tools

and the advent of Lean Six Sigma, we have seen other industries using this methodology.

The graph below show the percentage of articles, by year, related to manufacturing.

Figure 12: The Percentage of Articles Focused On Manufacturing Topics

From Figure 12, we see that the percentage of manufacturing articles is currently

decreasing although there has been fluctuation. We thought going into this study that this

might be the trend due to companies in other industries starting to use Lean Six Sigma for

continuous improvement. Then we decided to analyze the data further by looking at the

details of the specific areas in which the articles were concentrated.

Figure 13: Percentages of Articles by Different Areas

As you can see from Figure 13, the area of Healthcare provided the backdrop to the most

articles in our search followed by manufacturing. There were a considerable number of

articles that did not fit one of our main category areas and our grouped under the title

“Other.” Almost one quarter of the articles in our database came from other areas, thus

signifying the outreach of lean six sigma methodology in today’s business environment.

We then wanted to see where most of the authors were from and if there were any

conclusions that could be drawn from that data. As initially hypothesized most of the

authors in our database were from the United States, however, it is somewhat surprising

that the United Kingdom was the home for the second most, tied with China at 18. China

{T-2}, Taiwan {4}, and India {5} made sense to be where most authors were from since

there has been a global shift in the manufacturing and supply chain industries.

Figure 14: Number of Articles from Country of Origin

Research Topics and Methods

We then turned to the various research topics and methods that were used in the

articles that made up the database. We consolidated the categories to Theoretical with

Application, Case Study, Comparative, Literature Review, Survey, and Other. This

information will allow us to make some conclusions about the research articles in our

database that can be used to support our hypotheses or predict future research.

Figure 15: Pareto Chart of Articles by Research Approach

From the graph, most of the articles in the database used some type of applied theory as

the research approach then case studies were the second most popular. As one could tell

by adding up the numbers, there were some articles that incorporated multiple research

methods into their article. This methodology can be very effective when comparing two

methods such as Lean and Six Sigma and then giving a “real world” example or case

study to back up the comparative. The compositions of article origins and type are similar

to the results from Brady and Allen (2006) indicating stability over time.

Success Factors

In our literature database, 26% of the articles made specific reference to at least

one “success factor” that was necessary for success. We identified 13 distinct success

factors mentioned by Brady and Allen and originally by Sousa and Voss to describe the

dimensions of quality management practices. The graph below shows the percentage of

articles that specifically mention on these specific success factors.

Figure 16: Percentage of Articles That Has Specific Success Factor

As you can see from the graph, Structured Approach is the success factor that is most

referenced within the articles in the database. This is followed by Project Selection and

Top Management Commitment. These results follow what has been written about Lean,

Six Sigma, and Lean Six Sigma that one needs to be disciplined and hold true to a

structured approach from problem identification to data analysis to corrective actions.

Compared with results from Brady and Allen (2006), the results suggest a change in the

perception about project success factors. Previously, the emphasis was on top

management commitment (27% and now 11%) and now there is a greater emphasis on

the application of a structured approach (30% and formerly 8%). Intuitively, this might

be explained by greater acceptance among top management of six sigma related methods.

Synthesis and Future Research

In this section, we attempt to synthesize the results of our literature search and

project possible directions that future research might take. We also explore additional

data related to sustainability which our own personal experience suggests is related to

lean six sigma in part because the framework of lean six sigma is currently structuring

sustainability improvement and energy conservation efforts in many industries.

Evolution of Lean to Six Sigma to Green / Sustainability – Future Research

The theory behind the evolution from lean to Six Sigma to Lean Six Sigma to

sustainability here is that companies start with Lean tools to reduce cost and increase

throughput. These tools focus around head count optimization, downtime reduction and

ultimately an increase in throughput, which is usually measured in units per plant hour.

Then companies expand their tools to include Six Sigma which focuses around quality /

first pass yield indicators. As the opportunities become harder to come by, companies

look at green / energy reduction as a source of continuous improvement. The difficulty

with trying to do a literature search around sustainability or “green” is that there are so

many descriptors for that topic and a term such as sustainability may be used to describe

something that is not “green” and will pick up data that is not relevant. Therefore, we

show many graphical representatives that feel encompass “green” or sustainability and its

correlation to lean. In this first graph, the following charts show some of the literature

trends.

Our first look into this evolution was “Toyota Production System”, “Energy

Reduction” and “Lean.” As stated earlier, we used Toyota Production System (TPS) as a

search term because it is synonymous with lean methodology and we also used lean also

just so we picked up all relative articles. For our sustainability / “green” term, we used

energy reduction since it is very relevant to waste reduction, which is the mantra on Lean

/ TPS. We used Google Scholar for our literature search in order to stay consistent with

our earlier searches.

200

400

600

800

1000

1200

Years: 1990 - 1994 Years: 1995 - 1999 Years: 2000 - 2004 Years: 2005 - 2009

Subject Area: Engineering Subject Area: Business

Figure 17: Time Series of Google Search “Toyota Production System” + “Energy

Reduction + “Lean”

As you can see from the figure, the number of articles with these search terms has

increased significantly over the past twenty years. Again, this is not surprising since we

have already seen a significant increase in published articles with just the search term

Lean.

We also wanted to do variations of this search to see if we are seeing similar

trends in the literature. We wanted to see the results with the search terms “Lean” and

“Life Cycle.”

0 2000 4000 6000 8000

10000 12000 14000 16000

Years: 1990 - 1994

Years: 1995 - 1999

Y ears: 2000 - 2004

Years: 2005 - 2009

Subjec t Ar ea: Engineering Subjec t Ar ea: Business

Figure 18: Time Series of Google Search “Lean + Life Cycle”

In Figure 18, we are showing the results of the search Lean and Life Cycle. From the

graph, a similar trend is evident. Over the past twenty years, the number of research

articles increased significantly.

1000

2000

3000

4000

5000

6000

Years: 1990 - 1994 Years: 1995 - 1999 Years: 2000 - 2004 Years: 2005 - 2009

Subject Area: Engineering Subject Area: Business

Figure 19: Time Series of Google Search “Toyota Production System + Life Cycle”

Finally, we used the search terms “Toyota Production System” and “Life Cycle”. Again,

the same trend as we saw in Figures 17 & 18. We looked at other search terms, however,

the search picked up a lot of noise in the results that did not pertain to the criteria. Some

of the other search terms that were used were Sustainability, Green, and Metering.

Arnheiter and Maleyeff (2005) discussed the competitive advantage of Lean, Six

Sigma, and Lean Six Sigma and Pepper and Spedding (2008) amplified their discussion.

To their figure, we add the dimension of societal needs and the thread related to what we

call “green lean six sigma” (GLSS) which is predominantly focused on energy reduction

which has societal benefits. We argue that lean six sigma and GLSS offer a relevant

body of knowledge for sustainable systems engineering. Because we feel that there is

such a high value to society for GLSS, research and investment will continue to increase

over time.

Figure 20 – Green Lean Six Sigma’s Value to Society

Lean Six Sigma, Simulation, and Optimization – Future Research

Another forecast that we can derive from this research is that continuous

improvement seem likely to evolve from Lean Six Sigma in many organizations. These

High cost

Producer View pointLow cost

Society View point

Customer View point

Low value

High valueLow value

High value

Six sigma Lean Six sigma

Lean

“Green Lean Six Sigma”

organizations will move from Lean Six Sigma to Simulation and then finally to

Optimization. This will happen because it becomes ever so difficult to find the “low

hanging fruit” and companies still continue to strive to reduce costs within their

operations. Usually what you see is that Lean Manufacturing principles are the best tools

that allow an organization to reduce manpower and increase their units per man-hour.

Lean Manufacturing principles are the easiest to adopt since it the least difficult for

people to understand and thus adapt within their organization. Once this is not their

number one opportunity, companies need to look at first pass yield projects. The tools

that are best suited to do this are Six Sigma tools and thus the continuous improvement

tools must evolve. An organization never stops using the core tools that they have

developed / used but it is necessary to add additional tools to their initiatives to cut costs.

Within the literature that I examined, you can see the number of articles that contained

the terms Lean Six Sigma, Simulation and Optimization has increased over the past 6

years. Specifically, we did a Google Scholar search with the Search Terms: “Lean Six

Sigma”, “Simulation”, and “Optimization” from 2005 – 2010 where the search terms

would Appear Anywhere in the Article. The articles either appeared in “Business”

journals or “Engineering” journals.

Figure 21: Increase of Lean Six Sigma, Simulation, and Optimization Articles over

Time

As you can see from the graph, there is an upward trend in the number of articles

published with the terms Lean Six Sigma, Simulation and Optimization. With the limited

number of articles that were published from 2005 to 2010, it is not conclusive that there

is any true relationship between these identifiers; however, the theory needs to be

reviewed in the future.

We then took the opportunity to put together this theory with Lean Six Sigma,

Simulation, and Optimization and try to adapt it to the Capability Maturity Model. The

Capability Maturity Model (CMM was created by the Carnegie Mellon University

(CMU) and refers to a development model elicited from actual data. The data was

collected from organizations that contracted with the U.S. Department of Defense, who

funded the research, and became the foundation from which CMU created the Software

Engineering Institute (SEI). Like any model, it is an abstraction of an existing system.

[Information taken from Wikipedia.com]

The Capability Maturity Model (CMM) was originally developed as a tool for

objectively assessing the ability of government contractors' processes to perform a

contracted software project. The CMM is based on the process maturity framework first

described in the 1989 book Managing the Software Process by Watts Humphrey. It was

later published in a report in 1993 (Technical Report CMU/SEI-93-TR-024 ESC-TR-93-

177 February 1993, Capability Maturity Model SM for Software, Version 1.1) and as a

book by the same authors in 1995. [Information taken from Wikipedia.com]

We feel that if we use the CMM model and applied it to continuous improvement,

it allows for an effective approach toward improving overall operations. We took the

concepts of Lean Manufacturing, Six Sigma, Lean Six Sigma, Simulation, and

Optimization and applied it to the CMM. In Figure 22, you can see how continuous

improvement is applied to the CMM and how organizations can apply it.

Figure 22 – Capability Maturity Model – Continuous Improvement

Figure 22 is our interpretation of a Capability Maturity Model for Continuous

Improvement. As companies move upward on the CMM – Continuous Improvement

chart, a higher level of skill set is needed by all involved. Due to these skill set

requirements, it has been a deterrent for most companies to progress higher than level 3

{Lean Six Sigma}. However, we believe as the workforce becomes more educate, thus

with a higher level of skill, companies will move into levels 4 and 5.

Conclusions

We have categorized the literature relating to six sigma, lean six sigma, and

related topics. We have seen evidence that there has been a measured increase in the

overlap of literature on lean and six sigma but that the six sigma topic continues to be far

more popular than lean six sigma or lean.

We have also seen an increase in exploration of topics associated with relatively

mature organizations including those relating to optimization and simulation. The

observed evolution in the perceived project success factors which formerly focused on

management commitment and now focus on structured approaches probably reflects

growing organizational acceptance and maturity levels. Further, we introduced a diagram

which intuitively maps out concepts attempting to put the green or sustainability into the

context of six sigma related literatures. We believe continuous improvement will

continue to evolve and become more important in all sectors of business not just

manufacturing. With the advent of sustainability and its importance to the customer, this

could lead to the next frontier of continuous improvement or we can see the movement to

a more technical transformation from simulation then to optimization.

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Appendix A: Additional Figure and Table

Figure 23 – Screen Shot of the Science Citation Index Search Screen

Table 2: List Of Journals or Proceedings with at least one article in the study

134th TMS Annual Meeting – Technical Session International Journal of Quality & Reliability Management 14th International Conference of Industrial Engineering and Engineering Management International Journal of Services and Operations Management 17th International Euroma Conference International Journal of Six Sigma and Competitive Advantage 1st Annual IEEE Systems Conference Journal for Healthcare Quality 2005 IEEE International Engineering Management Conference Journal of Accountancy 2007 Crystal Ball User Conference Journal of Advances in Management Research 2008 Systems and Information Engineering Design Symposium Journal of Ambulatory Care Management 2009 International Conference Journal of Business Strategy 2010 Construction Research Congress Journal of Chemical Health and Safety 2010 Prognostics and Systems Health Management Conference Journal of Engineering Technology 214th ECS Meeting Journal of Financial Transformation 21st Annual Meeting of the Eastern Association for the Surgery of Trauma Journal of Healthcare Quality 41st Annual Autotestcon Conference Journal of Investigative Medicine 59th Annual Meeting of the American Association for Clinical Chemistry Journal of Laboratory Medicine 5th Wuhan International Conference on E-Business Journal of Manufacturing Technology 62nd Annual Meeting of the American Association of Blood Banks Journal of Manufacturing Technology Management 97th Annual Meeting of the United States and Canadian Academy of Pathology Journal of Medical Biochemistry Acquisition Research Program Journal of Operations Management American Journal of Roentgenology Journal of Product Innovation Management Annual International Conference of the IEEE Engineering in Medicine and Biology Society Journal of the Faculty of Engineering and Architecture of Gazi University AORN Journal Journal of the Healthcare Financial Management Applied Mechanics and Materials Journal of Thrombosis and Thrombolysis Asian Journal on Quality Journal of Trauma Injury Infection and Critical Care ASME 2008 International Mechanical Engineering Congress and Expo Journal of Validation Technology Benchmarking: An International Journal Journal on Quality and Patient Safety Business Process Management Journal Lab medicine China Market Retail Today Laboratory Medicine Clinical Chemistry Manufacturing Engineering Clinical Leadership & Management Review Measuring Business Excellence College & Research Libraries Operations Management Conference of the Portland International Center for Management of Engineering and Tech Operations Management Research Construction Research Congress 2010 Pharmaceutical Engineering Defense Technical Information Center Pharmazeutische Industrie First International Conference on Improving Construction Proceedings of the 2010 International Conference on Public Administration Frontiers of Health Services Management Production Planning & Control Gastrointestinal Endoscopy Public Money & Management Genetice Engineering News Quality and Reliability Engineering International Global Journal of Flexible Systems Management Quality Management in Health Care Healthcare Executive Quality Management Journal Healthcare Quarterly Radiologic Technology Human Interface and the Management of Information Radiology Management IMECE2008: ASME International Mechanical Engineering Congress SAE 2006 World Congress & Exhibition Implementation Science SAE International Industrial Engineering Journal Second International Conference on Six Sigma Industrial Engineering and Engineering Management SME Technical Paper Industrial Engineering and Management; 2010 IEEE Conference Strategy & Leadership Information Management Journal Tehnicki Vjesnik Technical Gazette Injury Prevention The Journal of Organizational Leadership & Business Interfaces The School of Computing and Technology 4th Annual Conference International Business Research The School of Computing and Technology 5th Annual Conference International Conference on Industrial Engineering The TQM Journal International Journal of Manufacturing Research The TQM Magazine International Journal of Process Management and Benchmarking Total Quality Management & Business Excellence International Journal of Productivity and Performance Management Value in Health International Journal of Production Research World Standardization &Quality Management