Lean Six Sigma in healthcare improvement

Since the late 20th century, Lean Six Sigma (LSS) has been a successful business model in manufacturing, improving efficiency, cost and value in business processes. The benefits of applying Lean in service industries has led to the same cost savings and efficiency effects that reduce process wastes in the service delivery process.1 An examination of relevant literature and applications of Lean Six Sigma in solving healthcare problems and challenges could provide an effective framework for reducing costs and improving healthcare service delivery.2

Lean Six Sigma background

Although Lean and Six Sigma were developed as distinct quality improvement principles, LSS was developed as a broader framework for quality improvements and process redesigns.3 Lean focuses on solving problems where all the variables and factors are known and the problem is linked to the flow of production. Conversely, Six Sigma works best when the problem is linked to value creation and involves a value-added step in the service or manufacturing process.4 Combining Lean and Six Sigma enhances the value and flexibility of a quality improvement framework.5

The success of LSS in manufacturing has led to widespread adoption in other industries including service and healthcare.6 LSS has become an important step in improving cost-effectiveness of healthcare service delivery. LSS adoption in the Netherlands and Red Cross Hospitals proved that the model could improve the overall quality of care while promoting cost-effectiveness, efficiency, and the reduction of redundancies and waste.

Cost issues in the U.S. healthcare industry

As of 2020, the United States spent more on healthcare than any developed nation in the world.7 However, not all Americans have equal access to healthcare.8

The U.S. healthcare system is fraught with inefficiencies, redundancies, overcharging, misallocation of resources and red tape.9 In fact, the United States spends significantly more on healthcare administrative costs than other developed nations.10

In 2019, there was an estimated $760 to $935 billion in waste and redundancies in the U.S. healthcare system.11 This is about 30% of total aggregate spending by the U.S. healthcare system.12 Some areas of healthcare linked to waste and inefficiencies include issues with the coordination of care ($165.7 billion), overtreatment or use of low-value care ($78.2 billion), overpricing of services and goods ($83.9 billion), and administrative costs ($265.6 billion).13 Addressing these areas is important to help make the U.S. healthcare system more cost-effective, efficient and affordable. If left unchecked, healthcare spending will become unsustainable in the next 20 to 50 years.14

How can Lean Six Sigma be used to improve efficiency in healthcare and lower aggregate healthcare spending by reducing complexity? To help answer this question, the author has conducted a systematic review of the literature on LSS utilization in healthcare. A literature search was conducted on PubMed, Embase, EBSCO, Cochrane and NIH, which resulted in 15 relevant peer-reviewed academic articles that applied LSS in various healthcare settings to solve process-related problems.

Literature review

Reducing hospital-acquired infections

Improta et al. (2017) investigated whether LSS could help reduce nosocomial diseases.15 The five-year study focused on applying LSS as a quality improvement framework in the general medicine, pulmonology, oncology, nephrology, cardiology, neurology, gastroenterology, rheumatology, and diabetology departments in a university hospital in Naples, Italy. The researchers used statistical analysis, cause and effect diagrams, and teams to identify and form solutions for reducing the incidence of hospital-acquired infections (HAI) in various departments.16

The study found that the increased use of data and root cause analysis improved the objectivity of the study and the types of solutions created and designed to address the problem.17 Moreover, solutions created to solve HAI also included appropriate controls and feedback mechanisms to assess the effectiveness of the solution using LSS framework.18 The researchers concluded that the use of a continuous improvement framework in healthcare could be used to improve the quality of healthcare QI processes and reduce waste by eliminating and correcting processes that lead to an increased risk for HAI.19 The study concluded that the use of LSS strategies and tools was well suited to reducing HAI risk from 0.36 to 0.19% after the five-year period.20

Medication errors and LSS implementation

LSS provides a problem-solving approach to organizational improvement aimed at addressing specific problems in healthcare. Trakulsunti and Antony (2018) conducted detailed case evaluations of successful LSS implementation designed to reduce medication errors in healthcare to identify key success factors.21 The study evaluated three case studies of successful LSS deployment in healthcare to reduce medication errors in in-patient and outpatient settings.22

Trakulsunti and Antony found that successful LSS deployment was linked to staff training on the purpose, uses and strategies used in LSS implementation. The study also found that effective and open communications before, during, and after LSS deployment was integral in assuring successful use of LSS in reducing medication errors in in-patient and outpatient settings.23 Another key finding was the role leadership played in successful LSS implementation.24 Leaders who had a clear goal and vision for change communicated effectively and empowered employees as part of the successful deployment of LSS-based solutions and quality management in healthcare organizations.25 Moreover, other pertinent factors in LSS deployment included the use of a project management approach to program planning and implementation, the level of investment, access to resources, management support for LSS framework adoption, and the use of quality teams.26

Reducing patient wait times

Godley and Jenkins (2019) conducted a research study to reduce patient wait times in the radiology department of a large acute care hospital. The researchers conducted a quality improvement project using LSS as a problem-solving, quality improvement strategy that boosted customer experience and addressed issues linked to lengthy patient wait times.27 Similarly, Ahmed et al. (2016) studied whether LSS implementation could reduce wait times and improve patient experience in the emergency department. Using LSS framework, the main problems affecting patient wait times and patient experience were identified. The researchers found that the main issues driving patient complaints were long wait times and lengthy treatment times.28 The LSS framework aided in identifying issues in the ED including constraints linked to the limited physical space of the ED, the volume of patients during peak hours, and the lack of fixed procedures to reduce overcrowding.29

Ahmed et al. concluded that the use of LSS has the potential to improve healthcare processes because it helps quality improvement teams identify specific process-related problems, pinpoint possible solutions, and develop practice improvement strategies that would effectively address these issues.30 The researchers also identified factors that prevented the effective application of LSS in healthcare, which included a lack of funding for LSS integration, a lack of human resources or commitment from management to devote resources to LSS integration, and a lack of training on LSS strategies and tools.31

LSS and fall prevention programs

An effective fall prevention program is integral in promoting care and wellness in hospitals, acute care, and long-term care. Kubilius et al. (2015) used LSS Define, Measure, Analyze, Improve, Control (DMAIC) as a change management tool to reduce the rate of falls, trips and slips among patients and staff using changes in the environment and care delivery processes.32

The quality improvement study applied LSS framework to collect and use data to identify, define and measure the problem.33 Second, LSS framework was used to identify possible solutions that could address falls in the hospital. Root cause analysis was used to identify fall risk factors such as patient and worker age who experienced falls, floor surface of the hospital, physical layout of the hospital, and weather.34 The QI team used the findings of the risk analysis to identify a risk pyramid that classified and showed the prevalence of STF risk in hospitals for patients and staff.35 The study found that the use of LSS has helped with the identification of problem-related factors and change management and concluded that the use of LSS is effective in addressing falls in hospitals.36

LSS and improvements in discharge procedures

One of the vulnerable areas in healthcare delivery is discharge and transfer of care. Niemeijer et al. (2016) tested whether LSS was a good fit for implementing a quality improvement study that improved critical to quality procedures (CTQ) during patient discharge and transfer procedures from the trauma nursing department.37 They wanted to determine if the use of an LSS framework would make quality improvement initiatives more effective and improve long-term adherence to QI strategies.38

The research findings show that the use of LSS adoption strategies for CTQ improved discharge procedures through the effectiveness of discharge recommendation by reducing the length of stay post-discharge from the trauma department from eight days to three days.39 Additionally, hospital efficiency was improved during the implementation with an additional 118 admissions at the same cost to the hospital’s operating cost for the same period.40 The patient cost associated with the new discharge and transfer procedure increased by $1,740, but the quality of care improved and the length of stay decreased.41 Based on the results, the researchers concluded that quality improvement programs using LSS improve quality of care by significantly reducing the patient’s length of stay, improving the appropriate type and level of care patients receive, streamlining the care delivery process, and eliminating wasteful procedures associated with the delivery of care.42

Similarly, Warren et al. (2018) conducted a quality improvement study to determine if the use of a valued team improved the discharge timeline in a large, 627-bed tertiary care academic hospital. The QI study adopted the LSS implementation framework to change the discharge process in the hospital.43 Warren et al. used the DMAIC framework of LSS as a change management framework for their QI program.44 Implementation time for the study was 18 months across various departments in the hospital.45

The results show that patients assigned to the intervention group were discharged  before 10 a.m., while those in the control group were released after lunch.46 The results also show that speedier discharge times were not associated with the quality of care, and the rate of readmission remained independent from changes in the discharge time.47 The study focused on reducing the discharge steps by redesigning the discharge process.48 The researchers provided a discharge process map before and after LSS adoption.49 Warren et al. used the Ishikawa Diagram for the root cause analysis of the problem.50 Transfer instructions, care coordination with post-acute care facilities, pharmacy, and equipment were identified as problem areas that increased the risk of delays.51 Knowledge of these problem areas was helpful in the redesign of the discharge process.52

Warren et al. concluded that the use of LSS is a good framework for identifying hard-to-detect problem areas or tasks that create inefficiencies and redundancies in the workflow.53

Hospital-wide adoption of LSS in hospitals

Barberato Henrique and Godinho Filho (2018) investigated the quality of LSS adoption in hospitals practicing continuous improvement (CI). The researchers used a systematic review methodology to examine the quality of LSS adoption among hospitals. The researchers examined the adoption of Lean only, Six Sigma only, and LSS in hospitals to see which model was adopted the most and yielded the most success.54 Among the 118 research studies collected, 72 studies between 2004 and 2017 conducted theory verification studies.55 About 22%, or 26 studies, used LSS while the majority of the studies (63%) used Lean only.56 Aside from this, the majority (86%) of the studies initiated continuous improvement programs with elements of Lean in the QI initiatives.57 Some of the studies did not include details on how CI techniques were further integrated into organizational processes.

LSS and hospital performance

Honda et al. (2018) conducted a meta-analysis to evaluate the benefits of LSS and Six Sigma in QI initiatives that focus on improving performance and efficiency.58 The study used 33 different randomized controlled trials (RCTs) to determine if LSS is useful for improving performance in the healthcare workplace and not just for addressing specific quality issues in various departments.59

The systematic review found that the use of Six Sigma and LSS in healthcare was prevalent at multiple levels.60 Lean and Six Sigma have been used separately and together to address issues that occur in various departments.61 Surgical, general medicine, laboratory and imaging, administration, and emergency medicine were most associated with quality-related implementations using LSS, Lean, and Six Sigma.62 Honda et al. also found that the use of the Ishikawa Diagram, Statistical Analysis, SIPOC, and VSM were the most popularly adopted LSS tools used in LSS, Lean, and Six Sigma healthcare organizations.

The researchers also found that organizational factors were important drivers and barriers for LSS, Lean, and Six Sigma adoption in healthcare. They cited training, awareness, and knowledge of Lean and Six Sigma principles, concepts, and implementation framework as the most crucial factor in LSS adoption success.63 Additionally, management support in the form of a clearly identified internal project champion (IPC) plays a crucial role in reducing resistance to change and more successful adoption of LSS framework in various QI organizational initiatives.64

The study concluded that LSS implementation and integration in the QI processes in the healthcare workplace is contingent on a variety of formal and informal organizational factors.65 These factors influence how well LSS would be integrated into the organization’s culture, work processes and internal environment.66 The researchers suggested that future studies focus on identifying the mechanisms that make adoption factors either facilitators or barriers.

Integrating LSS in organizational culture

Knapp (2018) investigated factors influencing LSS adoption in healthcare organizational culture. The researcher conducted a large sample survey (n= 446) of hospital managers and supervisors to identify cultural factors that affect LSS adoption in healthcare organizations. The study theorized that LSS adoption in healthcare is a growing trend and most adopters do not target organizational culture when planning and implementing LSS integration in the healthcare workplace.67

One of the main drivers is the need for improving cost and efficiency in hospitals to meet regulations and compliance standards, as well as improving patient safety.68 Organizational culture has been associated with change and quality improvements in organizations in various industries.69 The questionnaires used in the study were analyzed using multivariate analysis to determine the relevant factors affecting the relationship between LSS adoption and LSS integration in organizational culture.70 The study used a sample of healthcare managers, quality assurance officers, human resource managers and nurse supervisors.71

The study revealed three main factors influenced the adoption of LSS components into organizational culture: management support, infrastructure and methods of adoption.72 Among the three, strong management support led to better adoption of LSS and better integration into the organization’s culture. The MANOVA and ANOVA tests for management support were significant (F(3,100)1⁄44.89, p o 0.01, η2 1⁄4 1.28).73 This suggested that leadership and management factors were important in cultural changes and better adoption of LSS in the organization.74

An additional finding of the study reveals that the type of organizational culture influences the adoption and integration of LSS.75 Organizations with strong leadership and collaboration among groups and teams were more likely to adopt and apply LSS.76 In contrast, the survey revealed that an organization with a strong hierarchical culture is less likely to adopt LSS because of the internal divisions created by hierarchies and the difficulty of adapting to and implementing change in rigid, hierarchical cultures.77

Quality performance improvements and LSS adoption

LSS is associated with improvements in process design in workflow or production flow. Most LSS adoptions in healthcare have focused on using LSS to target specific practice problems.78 Manaf et al. conducted an in-person survey of 1,007 hospital staff of private and public hospitals in Malaysia to determine if organization-wide adoption of LSS framework is appropriate for quality improvement projects.79 The authors hypothesized that LSS would be the best framework to integrate continuous quality improvement in healthcare organizations.80

The results of the study revealed that LSS adoption in healthcare was varied and there were marked differences in adoption quality and adoption rates between private and public hospitals. Respondents from private healthcare organizations had a more favorable and positive view of Lean and Six Sigma as well as LSS principles and strategies. Lean management initiatives, Six Sigma initiatives, patient safety, and teamwork were common areas where private hospitals applied LSS.81

The mixed healthcare system of Malaysia demonstrated the gap in perception of quality and patient satisfaction between public healthcare and private healthcare organizations.82 Respondents who worked in private healthcare organizations were familiar with or reported practicing LSS, Lean, or Six Sigma principles in their QI programs at work while respondents from public hospitals did not report the same level of use or acceptance of LSS, Lean, or Six Sigma principles and strategies as observed in their workplace.83 The researchers noted that the type of service focus was an important factor influencing LSS adoption in private and public hospitals.84

Factors influencing failure of LSS implementation

LSS adoption is a complex process depending on the organization and the industry. Swarnakar et al. (2020) investigated the critical failure factors (CFF) that affect the rate and success of LSS adoption. They conducted a systematic review of empirical studies that evaluated LSS adoption and implementation in healthcare.85 The researchers wanted to identify critical factors that influence the success or failure of LSS adoption in quality improvement programs in healthcare organizations.86

The study found 14 CFFs that influenced the effects of the acceptance, planning, and implementation of LSS.87 The study concluded that the 14 CFFs fell under the categories of knowledge and learning, organization, economics and managerial, technological, social, and environmental.88 These CFFs influence various aspects of LSS implementation.

First, the study showed that poor leadership is an important CFF in LSS adoption because, along with lack of support from top management, it is crucial as it provides access to resources and lends legitimacy to the LSS-based QI programs.89

Second, sustainability is an important factor in LSS adoption.90 LSS is a flexible framework that could be used to solve several problems and quality issues in healthcare organizations. The sustainability of LSS adoption is important. It can help the organization successfully use and reuse LSS strategies and tools to address workflow, program, process and even systemic problems embedded in organizational culture.91 The sustainability of LSS implementation would ensure that LSS would be continuously used in all QI projects in the hospital.

Third, coordination and collaboration among providers are a top CFF in LSS adoption.92 The level of coordination and collaboration is essential in solving problems in healthcare organizations. In turn, the level of integration of different departments in the hospital dictates the level of coordination and cooperation in the organization.93 Thus, the level of integration in the healthcare organization and the level of cooperation are important in LSS adoption.94 Successful LSS adoption relies on the cooperation of the entire organization.95

Fourth, training and awareness are important knowledge-based CFFs.96 Management cannot succeed with its LSS implementation if employees are not aware of Lean or Six Sigma, or the combination of both.97 Training is an important part of any quality improvement program. The study found that ineffective training or insufficient instruction were linked to program failure.98 LSS implementation in the organization relies on the knowledge and competency of the staff that implements QI projects using LSS framework.99 A lack of knowledge and training would mean that the staff, supervisors, and managers would lack competence in using LSS for their QI programs.100

LSS and healthcare sustainability

Achieving sustainability is a top priority for every organization. Zhu et al. (2018) investigated whether healthcare organizations could use LSS to improve their sustainability by making improvements with their supply chain management and overall operational management. The researchers described the healthcare industry as an environmentally positive and low-impact industry.101 However, healthcare organizations could still benefit from improving their level of sustainability as a means of improving efficiency, productivity and overall costs.102

The study tested the use of LSS as a productivity enhancement framework for healthcare organizations.103 The researchers used an organization-wide strategy to integrate LSS into the entire healthcare organization targeting the healthcare supply chain, operational management, inventory, procurement, storage and quality control.104 The researchers applied the Toyota model for Lean and integrated Six Sigma into their experimental framework.105 They theorized that the use of Lean as a framework for productivity is ideal because it emphasizes collaboration, shared goals, shared process understanding, and a problem-solution-focused approach to identifying and fixing errors using a quality-improvement approach.106

On the other hand, Six Sigma’s framework emphasizes quality improvement that seeks to reduce defects that undermine the quality-of-service output.107 They investigated the effects of using Lean and Six Sigma in improving the sustainability of linen operations, medication delivery system, sanitation, and waste management in the sample hospital.108

The results of the study reveal that among the three case studies included in the research, LSS was most effective in improving linen operations and sterilization, sanitation, and waste management.109 The study showed that the processes for these functions had some inefficiencies and unsustainable practices while the medication delivery system did not have the same critical quality issues and unsustainable practices.110 The study results reveal that an organization-wide QI could help identify processes in need of improvement and others that only need minimal improvements.

Discussion and conclusion

LSS has the potential to serve as a flexible quality improvement framework that could be applied in the department, organization, and system levels of healthcare. LSS combines Lean Thinking and Six Sigma, which could provide healthcare management and leadership the tools they need to improve processes and workflows in their organizations. LSS is a quality-focused framework and because of this, it is well suited for healthcare.

The U.S. healthcare system is in dire need of improvement and change. Economic changes should focus on improving the cost-effectiveness of healthcare service delivery. Socially, healthcare should improve accessibility and reach to allow the same level of access for everyone. Quality and efficiency should become the top priority of healthcare reform. While the goals are clear, the solutions remain the same.

The literature review revealed that LSS is useful for the development of a workable and effective quality improvement framework that could be adopted by all healthcare organizations. LSS has been developed to initiate continuous improvement in various organizational settings. While continuous improvement and LSS have been developed for the manufacturing industry, its use in the service industry has grown over the years. LSS is now a popular quality improvement and change framework for various types of services, including customer care and hospitality. This suggests that LSS could be modified, updated and applied to the context of healthcare.

Evidence from the literature revealed that Lean, Six Sigma, or a combination of both could be used to address persistent practice problems, such as hospital-acquired infections, patient falls, healthcare staff injuries, medication errors, and discharge times. These practice problems are tied to service delivery processes, and could be solved with the use of LSS strategies and tools applied in the context of healthcare.

LSS is a problem-solving strategy and a quality improvement framework that aids and empowers organizations to create a positive culture that supports a learning organization that embraces change and improvement. Evidence from the studies surveyed in the literature review reveals that LSS could be applied in organization-wide efforts to improve organizations such as hospitals, clinics and long-term care facilities. Unlike other change frameworks, LSS is quality- and process-oriented. Because of this, it is an important framework that could be leveraged by healthcare organizations to improve their overall quality and help them adapt to changing industry demands.

Notes:

1. Rathi R, Vakharia A, Shadab M. “Lean Six Sigma in the healthcare sector: A systematic literature review,” Materials Today: Proceedings, 2021. doi.org/10.1016/j.matpr.2021.05.534.
2. Ibid.
3. Manaf S, Ahmed NH, Islam R. “Measuring Lean Six Sigma and quality performance for healthcare organizations,” International Journal of Quality and Service Sciences, 2018, 10(3), 267-278. doi.org/10.1108/ijqss-09-2017-0076.
4. Ibid.
5. Ibid.
6. Rathi, et al.
7. Harvard Health. “The most expensive health care system in the world.” News Harvard Health, Jan. 13, 2020. Available from: bit.ly/3zmuXXg.
8. Ibid.
9. Chen F, Liao JM. “Can Medicare for all control health care costs?” Family Medicine, 2020, 52(1), 75-76. doi.org/10.22454/fammed.2020.620564.
10. Ibid.
11. Shrank WH, Rogstad TL, Parekh N. “Waste in the US health care system,” JAMA, 2019, 322(15), 1501. doi.org/10.1001/jama.2019.13978.
12. Ibid.
13. Ibid.
14. Ibid.
15. Improta G, Cesarelli M, Montuori P, Santillo LC, Triassi M. “Reducing the risk of healthcare-associated infections through Lean Six Sigma: The case of the medicine areas at the Federico II University hospital in Naples (Italy),” 2017, Journal of Evaluation in Clinical Practice, 24(2), 338-346. doi.org/10.1111/jep.12844.
16. Ibid.
17. Ibid.
18. Ibid.
19. Ibid.
20. Ibid.
21. Trakulsunti Y, Antony J. “Can Lean Six Sigma be used to reduce medication errors in the health-care sector?” Leadership in Health Services, 2018, 31(4), 426-433. doi.org/10.1108/lhs-09-2017-0055.
22. Ibid.
23. Ibid.
24. Ibid.
25. Ibid.
26. Ibid.
27. Godley M, Jenkins JB. “Decreasing wait times and increasing patient satisfaction,” Journal of Nursing Care Quality, 2019, 34(1), 61-65. doi.org/10.1097/ncq.0000000000000332.
28. Ahmed S, Manaf NH, Islam R. “Effects of Lean Six Sigma application in healthcare services: A literature review,” Reviews on Environmental Health, 2016, 28(4). doi.org/10.1515/reveh-2016-0015.
29. Ibid.
30. Ibid.
31. Ibid.
32. Kubilius A, Winfrey K, Mayer C, Johnson G, Wilson T. “Applying Lean Six Sigma tools to reduce the rate of slips, trips and falls for Joint Commission field staff,” International Journal of Six Sigma and Competitive Advantage, 2015, 9(1), 37. doi.org/10.1504/ijssca.2015.070089.
33. Ibid.
34. Ibid.
35. Ibid.
36. Ibid.
37. Niemeijer GC, Trip A, Ahaus KT, Does RJ, Wendt KW. “Quality in trauma care: Improving the discharge procedure of patients by means of Lean Six Sigma,” Journal of Trauma: Injury, Infection & Critical Care, 2016, 69(3), 614-619. doi.org/10.1097/ta.0b013e3181e70f90.
38. Ibid.
39. Ibid.
40. Ibid.
41. Ibid.
42. Ibid.
43. Warren M, Molla DS, Stewart SL, Stocking J, Johl H, Sinigayan V. “A Lean Six Sigma quality improvement project improves timeliness of discharge from the hospital.” The Joint Commission Journal on Quality and Patient Safety, 2018, 44(7), 401-412. doi.org/10.1016/j.jcjq.2018.02.006.
44. Ibid.
45. Ibid.
46. Ibid.
47. Ibid.
48. Ibid.
49. Ibid.
50. Ibid.
51. Ibid.
52. Ibid.
53. Ibid.
54. Barberato Henrique D, Godinho Filho M. “A systematic literature review of empirical research in Lean and Six Sigma in healthcare,” Total Quality Management & Business Excellence, 2018, 1(18), 3-15. doi.org/10.1080/14783363.2018.1429259.
55. Ibid.
56. Ibid.
57. Ibid.
58. Honda AC, Bernardo VZ, Gerolamo MC, Davis MM. “How Lean Six Sigma principles improve hospital performance,” Quality Management Journal, 2018, 25(2), 70-82. doi.org/10.1080/10686967.2018.1436349.
59. Ibid.
60. Ibid.
61. Ibid.
62. Ibid.
63. Ibid.
64. Ibid.
65. Ibid.
66. Ibid.
67. Knapp S. “Lean Six Sigma implementation and organizational culture,” International Journal of Health Care Quality Assurance, 2018, 28(8), 855-863. doi.org/10.1108/IJHCQA-06-2016-0079.
68. Ibid.
69. Ibid.
70. Ibid.
71. Ibid.
72. Ibid.
73. Ibid.
74. Ibid.
75. Ibid.
76. Ibid.
77. Ibid.
78. Manaf, et al.
79. Ibid.
80. Ibid.
81. Ibid.
82. Ibid.
83. Ibid.
84. Ibid.
85. Swarnakar V. Singh A. Tiwari AK. “Evaluating the effect of critical failure factors associated with sustainable Lean Six Sigma framework implementation in healthcare organization,” International Journal of Quality & Reliability Management, 2020, 38(5), 1149-1177. doi.org/10.1108/ijqrm-07-2020-0243.
86. Ibid.
87. Ibid.
88. Ibid.
89. Ibid.
90. Ibid.
91. Ibid.
92. Ibid.
93. Ibid.
94. Ibid.
95. Ibid.
96. Ibid.
97. Ibid.
98. Ibid.
99. Ibid.
100. Ibid.
101. Zhu Q. Johnson S, Sarkis J. “Lean Six Sigma and environmental sustainability: A hospital perspective,” Supply Chain Forum: An International Journal, 2018, 19(1), 25-41. doi.org/10.1080/16258312.2018.1426339.
102. Ibid.
103. Ibid.
104. Ibid.
105. Ibid.
106. Ibid.
107. Ibid.
108. Ibid.
109. Ibid.
110. Ibid.