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Rev Environ Health 2019; 34(4): 427–434
Review
Selim Ahmed*
Integrating DMAIC approach of Lean Six Sigma
and theory of constraints toward quality
improvement in healthcare
https://doi.org/10.1515/reveh-2019-0003
Received March 25, 2019; accepted May 27, 2019; previously
published online July 17, 2019
Abstract: Healthcare is a unique service industry and it
deals with complex tasks. To overcome complex tasks,
healthcare organizations need to implement DMAIC
(Define, Measure, Analyze, Improve, Control) approach
of Lean Six Sigma (LSS) to improve quality performance.
Application of DMAIC in a healthcare organization pro-
vides guidelines on how to handle a quality service sys-
tem toward patient satisfaction. This approach also helps
healthcare service providers to reduce waste, variation
and work imbalance in the service processes. This chapter
discusses five phases of DMAIC approach and its integra-
tion with the theory of constraints (TOC) for continuous
improvements in healthcare performance. The integration
of TOC and DMAIC approach would enhance healthcare
performance by reducing medical costs, medical errors,
administration errors and defects. Moreover, this integra-
tion can improve performance in healthcare service pro-
cesses where it is not possible to reduce bottlenecks.
Keywords: DMAIC approach; healthcare; Lean Six Sigma;
quality improvement; theory of constraints.
Introduction
In 1950s, the Lean Production System was introduced by
Taiichi Ohno who worked at Toyota as an engineer. The
purpose of this approach was to reduce waste and improve
quality performance in production processing. This system
was first implemented by the Toyota Company to enhance
value-added activities and reduce non-value-added (NVA)
parts in the automobile production process (1, 2). By intro-
ducing this approach, Toyota was able to beat Ford and
became the second largest world car producer in 2004.
After 2years, Toyota profits increased to USD 12 billion,
whereas Ford lost USD 12.7 billion and General Motors
(GM) lost USD 3.4 billion (3). In 2008, Toyota beat GM
and became the world’s greatest automobile producer.
In 1990s, Xerox Corporation modified the Lean Produc-
tion System as a Lean method and implemented it in their
supply chain management process. In 2002, Xerox inte-
grated Lean and Six Sigma methods together and named
it “Lean Six Sigma (LSS)”. The main reason for this inte-
gration was to improve the quality production process by
eliminating errors and reducing costs. Once the Xerox Cor-
poration succeeded in implementing the LSS method in
their production process, many healthcare organizations
started to adopt this approach to improve their quality
service toward patient satisfaction (4, 5).
In addition, integration of Lean and Six Sigma
approaches can improve the quality performance of the
healthcare organization by increasing patient care toward
satisfaction and loyalty. The LSS method ensures quality
performance of the healthcare organization by reducing
error in the medical test report, waiting time, costs and
delivering test report (6, 7). According to De Koning etal.
(8), the LSS method has a strong effect on developing
innovative health service by reducing costs and errors
such as the radiology department of Virtua Health reduced
medication and laboratory errors and improved patient
safety by implementing the LSS application. Similarly, the
Commonwealth Health Corporation implemented the LSS
approach in the project of the infection control group and
they succeeded in reducing the infection rate by over 65%
within a few years. The LSS approach not only reduces
waste and costs but also establishes a culture of continu-
ous quality improvement in a healthcare organization to
ensure accurate outcomes in a timely fashion (9).
Application of DMAIC in healthcare
Application of DMAIC (Define, Measure, Analyze, Improve,
Control) approach in a healthcare organization provides
*Corresponding author: Selim Ahmed, World School of Business,
World University of Bangladesh, Plot – 3/A, Road – 4,
Dhanmondi, Dhaka – 1205, Bangladesh,
E-mail: selim.ahmed@business.wub.edu.bd.
https://orcid.org/0000-0002-0361-6797
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428 Ahmed: Integrating DMAIC approach of LSS and TOC toward quality improvement in healthcare
guidelines on how to handle the organizational employ-
ees’ perspective of each phase toward better quality per-
formance (10, 11). One of the key advantages of applying
the LSS DMAIC process is that it prevents duplication
process and continuously improves quality performance.
Through the LSS approach, the organization’s employees
and experts (i.e. Black Belt and Green Belt holders) will
understand why both Lean and Six Sigma are necessary
to maximize organizational performance (12). Figure 1
shows the LSS DMAIC process tools followed by a detailed
discussion.
Define
In the define phase, the top management of healthcare
organization must clearly define the project objective
and scope for the team according to the agreement. The
top management needs to explain to the team “what the
project is and what it should accomplish” to determine
the needs of the customers (13). Precisely, the main task
of the define phase is to analyze the project target and its
duration. The define phase must confirm the understand-
ing between the team and the management (10). Both the
team and the healthcare management (sponsor) should:
i Agree on the problem: what are the main issues that
affect the patients, what are the main factors to deter-
mine the voice of the customers (VOC), how the pre-
sent performance fulfil the desires of patients toward
satisfaction;
ii Understand the corporate strategy and its relation-
ship with return on investment capital (ROIC);
iii Agree on the limitations of the project; and
iv Identify what indicators will be applied to measure
the success of the healthcare organization.
The abovementioned points are important in service
organizations except the second point. When a process
map is designed, the organization normally defines the
project boundaries by identifying the starting and ending
points on the project map (14). However, these LSS pro-
cesses of mapping will not work if people issues are not
Define
Measure
Analyze
Improve
Control
Project selection tools
PIP management process
Value stream map (VSM)
High level process map
Financial analysis
Project charter
Stakeholder analysis
Kano analysis
Communication
plan
Voice of customer
(VOC)
Operational definitions
Data collection plan
Pareto chart
Histogram
Box plot
Statistical sampling
Measurement system
analysis
Control charts
Process cycle
Process performance
Pareto charts
Cause & Effect (C&E) matrix
Fishbone diagrams
Brainstorming
Constraint
identification
Time trap analysis
Non-value-added
analysis
Hypothesis testing
Confidence intervals
Analysis of variance
Queuing theory
Benchmarking
TPM (total productive
maintenance)
Line balancing
Process flow
improvement
Setup reduction
Generic pull
5S
Kaizen
Poka-Yoka
Solution matrix
Control charts
Standard operating
procedures (SOPs)
Project commissioning
Visual process control
Mistake-proofing
Process control plans
Training plan
Project replication
Plan-Do-Check-Act
(PDCA) cycle
Figure 1: Lean Six Sigma DMAIC process tools.
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Ahmed: Integrating DMAIC approach of LSS and TOC toward quality improvement in healthcare 429
defined properly. Two people issues must be defined in
the define phase, such as:
i The project leader must ensure that the right team
members are in the team. The team members should
not only be assessed by knowledge, experience and
training but also evaluated by their attitude and
performance.
ii The project leader must ensure that all team members
are engaged in the project. The team members should
start their project activities from the same page with
the same expectations. The more the team members
deliberately participate in the project and understand
the importance of the project work, easier it will be to
complete it (10).
The project leader of the LSS program should develop a
communication plan to provide information to the top man-
agement of the organization and receive feedback on the
progress and direction of the project. It is very important for
the project leader (Black Belt or Green Belt Champion) to
often meet the project owner or top management to inform
about the project results and processes (11). The project
leader should inform the project owner early if any changes
have been made in the project. The feedback of the project
owner would provide direction which will facilitate the pro-
ject’s success and implementation without complexity (15).
Measure
In this step, the measureable service indicators are identi-
fied according to the operational definition of critical to
quality (CTQ). This phase also identifies the input and
outcome measurements such as conducting process level
data collection, establishing baseline metrics, logically
placing array data in visual depictions and following
statistical rigor: sampling and reporting (13). The meas-
urement comprehends the VOC and then translates the
customer feedback into measurable design requirements.
The emphasis on VOC could be novel for those accus-
tomed to DMAIC projects. Although customer needs shape
the priorities in a DMAIC project, VOC analysis empha-
sizes an accurate understanding of the customer needs
as a vital determinant of success (16). To understand the
VOC, the team should measure the value stream mapping
(VSM) through:
i Data collection plan;
ii Current and future state map;
iii Determine specs for CQT;
iv Use histograms to characterize the variables that could
cause the quality issue under consideration; and
v Use variables search, scatter plots, response surface
methodology, Pareto charts or measurement check
sheets to focus attention on the vital few contributors
to the quality issue.
Unfortunately, it was observed that many people in service
organizations have misused data and statistics to justify
false arguments. Therefore, the project leaders should be
involved in data collection and processing. They should
ask the team members to decide what types of data should
be collected and why, and how it will be used to measure
the customers’ needs (10).
Analyze
This step analyzes the collected data and uses VSM to
identify and validate the causes of errors that affect the
NVA processes (17). This phase analyzes the informa-
tion collected in the measurement phase to identify the
sources of delays, waste and poor quality. In our analy-
sis, we use Pareto diagram, cause-and-effect diagrams,
scatter plots, design of experiments and 5 Whys analysis
as part of our LSS approach to map and explore the cause-
and-effect relationships (13).
In the analysis phase, the LSS team discovers prob-
lems in the service processes and determines the value-
added or NVA work for the customers. The value process
can be classified into three different categories:
i Customer value added (CVA): CVA only focuses on cus-
tomers’ value;
ii Business value added (BVA): Despite being useful for
businesses, customers do not derive value from this
category; and
iii Non-value added (NVA): It is an activity which has no
value from the customers’ viewpoint (18).
In most service processes, work such as calls, forms and
requests spends only 5% of its time in value-add and
the remaining 95% is spent for waiting around, being
reworked and so on. If the organization increases 20%
value-add work, then it will reduce 20–50% NVA work and
costs of the project. A well-trained Black Belt champion
can identify the problems in service processes and facili-
tate a team through a VSM event to determine the steps of
value-added and NVA work for the customers (16).
Improve
In this phase, the LSS project team eliminates the root
causes of defects which have influenced the CTQ process
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430 Ahmed: Integrating DMAIC approach of LSS and TOC toward quality improvement in healthcare
(13). More importantly, the improve phase makes changes
in the service processes by eliminating the defects, waste
and costs related to the customer needs as identified in the
define phase. This phase uses common tools and strategies
to select the best alternatives to meet the customers’ needs.
To select the best alternatives, the team must use the solu-
tion matrices tool, because it has a relationship with brain-
storming solutions, project purpose and methods to meet
customer needs (14). After selecting the best alternatives
for customer needs, the project leader should pay attention
to the implementation processes such as:
i The project leader should focus on project activities
closely and if there is anything wrong, the project
leader will immediately stop the process of the project
activity. Then, the project leader will figure out why
those problems occurred, and how it will be elimi-
nated to avoid delays or interruptions in the improve-
ment process;
ii Implement an action plan for eliminating the quality
issue; and
iii Plan a strategy for the removal of restraining forces
and the subtle promotions of driving forces.
However, nothing will be changed in the improve phase if
the project leader does not pay attention to people issues,
especially communication with team members, team
involvement and commitment. Team members could be
used as a sample to represent the larger group of people
who work on that process. Their work could be facilitated
by clear and regular communication with co-workers that
would support the achievement of the targeted goals.
They could share potential solutions, provide constructive
feedback on the work of colleagues and ask for help. The
concept of Kaizen can help define work tasks and measure
the extent to which they are being achieved. It supports
effective team work and proactive communication for
enhanced work performance (16).
Control
The control phase aims to achieve sustainable solutions.
Achieving this involves improving and controlling the
variables critical to process performance and tracking the
LSS process performance (19). The project team should
share their knowledge with others who will resume their
task and ensure that all members are working on the same
set of updated procedures. There are six important issues
of control in the service environment which must be fol-
lowed by the team to ensure improved process perfor-
mance (20, 21). These are:
i Ensure the improve process is recorded;
ii Turn the outcomes into cash (verified by the finance
division);
iii Maintenance of improvements must be confirmed
during the working process;
iv An automated monitoring system must be set up to
identify “out of control” performance;
v Organize the working process; and
vi Create a control plan.
According to Carreira and Trudell (18), a control process
plan usually builds on the future state process map, indi-
cating who is responsible for what is in the new process.
Therefore, the LSS team must keep in mind the causes of
the potential problems that could arise during the elimi-
nation of quality issues, and using control charts could
help monitor the variations of the potential problems.
Besides using the control chart, the team also needs to
implement the control plan by observing the statistically
significant variations and train the service operators to
run the integrated quality control (QC) system effectively,
and give them authority to make decisions during the
service process (22, 23).
Integrated theory of constraints
andLSS
The theory of constraints (TOC) was originally devel-
oped by Eliyahu M. Goldratt. It is a management philoso-
phy that focuses on continuous improvement processes
(24). The constraint is defined by Goldratt and Cox (25)
as that which prevents a system from performing at the
higher level than it currently does. TOC provides guiding
principles and concepts which are supported by a set of
logistical approaches to handle work processing flow
through the system. It uses logical tools to identify system
constraints and design and implement effective ways to
improve the work processing systems (26). The funda-
mental assumptions of TOC include system thinking that
views enterprises as a complete and complex system with
interacting constituent parts. It regards constraints as an
obstacle in the system that undermines peak performance
and that there must be at least one such constraint in the
system (25).
According to Choe and Herman (24), TOC seeks
to identify and address the constraint in the system to
enhance the performance and facilitate the achievement
of organizational goals. Choe and Herman (24) suggested
that the organizational managers or top management need
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Ahmed: Integrating DMAIC approach of LSS and TOC toward quality improvement in healthcare 431
to determine what types of constraint tools will be used
in the system processing for achieving the organizational
goals at the earlier step in improving a system. They also
mentioned that constraints can be divided into two parts of
the processing system: physical and nonphysical. Physical
constraints are often easier to address compared to non-
physical constraints which are hard to identify and resolve.
Dettmer (27) defined constraints as a set of tools that
change agents to increase organizational profits. Dettmer
also stated that the existence of constraints provides an
excellent opportunity for improvement of the organiza-
tional performance, because it allows the organizational
processing system to highlight the most productive area
through identifying and managing the constraints. There
are five steps of TOC which would help the organization
improve organizational processing. These are:
i Identify the system’s constraint;
ii Decide how to exploit it;
iii Subordinate/synchronize everything else to the above
decisions;
iv Improve the system’s constraint; and
v Return to step one, but beware of “inertia”. If the con-
straint has moved in the above steps, go back to step
one.
These five steps of TOC are related to the Lean processing
system which focuses continuously on quality improve-
ment in the management processing systems of the organ-
ization (28). The TOC can be used to improve the Lean
processing processes by eliminating bottlenecks (29).
It is a tool that has had proven success in management
processes, inventory and supply chains, project manage-
ment and decision-making, among others (30). Accord-
ing to Breen etal. (31), TOC offers a logical and rigorous
approach for analyzing and improving the performance of
a healthcare organization. This theory has been applied in
a number of areas in healthcare both in the United States
and the United Kingdom to improve quality processing
systems (31). Figure 2 illustrates the integration of LSS and
the TOC model.
According to Lepore and Cohen (32), TOC has a signifi-
cant relationship with the LSS approach when it comes to
improving the workforce management toward quality per-
formance of the organization. The integration of TOC and
the LSS approach enhances healthcare human resource
management practices, such as human resource plan-
ning and management, training, employee recognition
and job satisfaction. This integration helps healthcare
organizations in reducing medical costs, medical errors,
Define
Measure
AnalyzeImprove
Control
Patient waiting time
Cycle time in inpatient and
outpatient diagnostic
Billing process
Medical
costs
Patient
registration
Defects
Revenue cycle
Technical
requirements
Clinical
coding
Exploit
constraints
Subordinate
Elevate
TOC
Identification constraints
If breaks,
repeat
Employee
retention
Patient
satisfaction
Medical
errors
Administration
errors
Lean Six Sigma
Figure 2: Integration of Lean Six Sigma DMAIC method and TOC model in healthcare.
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432 Ahmed: Integrating DMAIC approach of LSS and TOC toward quality improvement in healthcare
administration errors and defects toward patient satisfac-
tion and loyalty. This integration also helps healthcare
organizations to recruit the best person for the job who
possesses the skills and traits to perform the assigned
tasks efficiently and exercise leadership. Such a person is
key to quality improvement in healthcare service (33, 34).
Grida and Zeid (35) conducted a study on the imple-
mentation of the TOC in Dar El-Shifa Hospital, Egypt.
Their research objective was how TOC assumptions
improve healthcare system by reducing waiting time in
the operating room. Based on their study, it was observed
that the implementation of TOC model helped the hospi-
tal to reduce the waiting time by 88%. This model also
helped the hospital to improve the overall performance
of the healthcare system by 6% and increase the doctor
availability by 40%. Sahraoui and Elarref (36) conducted
a study to reduce bed crisis and late cancellation of elec-
tive surgery in Hamad General Hospital, Doha, Qatar by
applying five steps of TOC. Their research findings indi-
cate that the TOC approach helps the hospital in analyz-
ing the healthcare system and finding better solutions
to reduce bed crisis and cancellation of elective surger-
ies. Pawlak (37) applied TOC techniques to eliminate the
shortage of nurse workforce in the United States. Accord-
ing to her research findings, it was observed that TOC
techniques help increase the availability of nurses in the
hospital along with commitment.
Discussion and conclusion
Hospitals are highly concerned with the quality perfor-
mance of their healthcare systems. To this end, they have
incorporated quality techniques such as plan-do-study-
act (PDCA), 5S, Kaizen, control charts and root cause anal-
ysis to achieve greater patient satisfaction (38). Studies on
healthcare performance have explored the various ways
to measure quality performance. This requires clearly
defined performance outcomes with quantifiable meas-
urements (39). Based on the assumption that quality per-
formance reflects good-quality practices, in addition to
the highly competitive nature of healthcare, hospitals are
always seeking ways to improve their performance and
increase patient satisfaction (38).
However, with the complexity of healthcare, its highly
specialized nature of many of its processes, the many
staff and broad scope of its activities, it becomes difficult
to measure quality performance (40). One of the difficult
tasks to measure healthcare performance is the attribu-
tion variability associated with a high level of cognitive
reasoning, problem solving, flexible decision-making and
experiential knowledge (41). It is also hard to ascertain
whether small mistakes were near misses or could have
caused significant harm (42).
To overcome the difficulties, the LSS and TOC model
need to be integrated to enhance value-added activi-
ties toward quality performance in healthcare organiza-
tions. This integration not only increases the value-added
activities but also reduces NVA activities (i.e. waste and
unnecessary services) for the continuous improvement
in healthcare quality performance (30). The DMAIC and
TOC approaches depend on root cause analysis to inves-
tigate waste and errors within organizational processes.
They support quality performance by eliminating waste
and errors (43). In healthcare organizations, they support
improvements in service quality performance. This inte-
gration also improves organizational human resource
management practices such as recruiting the most appro-
priate person for the job who ensures that the tasks of the
organization are executed as intended. This is vital for
quality improvement (44).
The present study mapped DMAIC with TOC assump-
tions to enhance the performance of the healthcare organ-
ization. However, due to less number of publications in
peer-reviewed journals, it is required to conduct more
research on DMAIC and its integration with TOC model
to contribute theoretical knowledge as well as practi-
cal implications. For theoretical contribution, a common
definition needs to be developed to distinguish between
DMAIC and TOC for strengthening the existing litera-
ture. This study provides needful information to define
both the approaches with examples. In addition, this
study also provides the appropriate guidelines on how to
analyze a healthcare system by integrating DMAIC and
TOC approaches toward quality performance. For practi-
cal implications, the healthcare organization needs to
obtain commitment and involvement of professionals for
successfully implementing the DMAIC and TOC models.
The implementation of these two approaches would help
the healthcare organization to analyze healthcare perfor-
mance such as patient safety, financial outcomes, patient
satisfaction and loyalty (45, 46).
Finally, from a strategic point of view, the integration
of DMAIC LSS method and TOC model links internal and
external performance of the healthcare organization. This
integration not only provides insights to practitioners
about the blueprint of the DMAIC and TOC for the continu-
ous improvement of healthcare quality performance, but
also creates a unique competency that may be difficult for
competitors to duplicate. It is essential that the top man-
agement of the healthcare service providers should spend
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Ahmed: Integrating DMAIC approach of LSS and TOC toward quality improvement in healthcare 433
time to understand both the applications and incorporate
these models into management oversight and strategic
planning for continuous improvement. When it is done
properly, both approaches can increase the value of the
healthcare services by improving quality performance.
Research funding: None declared.
Conflict of interest: Authors state no conflict of interest.
Informed consent: Not applicable.
Ethical approval: The conducted research is not related to
either human or animal use.
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