Literature Review: Lean Manufacturing Assessment During the Time Period (2008-2017)

The aim of this paper is to explore and evaluate previous work focusing on the relationship and links between Lean manufacturing and industrial work. This study reviews the literature on Lean Manufacturing Assessment (LMA) during the last decade; 2008–2017 and analyses the literature from different perspectives. This paper highlights various key words, scopes, objectives, case study, definitions, methodologies, tools and main results. A total of 126 research papers have been reviewed in this study to help the researchers in the evaluation of lean manufacturing practices to identify and benefit from these studies. This paper provides a quantitative descriptive analysis and qualitative thematic analysis to provide an analysis of impact of lean on performance. Consequently, this paper can be considered as a guide for researchers in LMA. It is expected to be a brief reference for future researchers that reduces effort and time consuming during their studies.


Introduction
This century is characterized by the rapid growth in all areas related to human life, such as education, health, industry and services. In line with this rapid growth is the lean applications, which include many applications that contribute to improving the performance in the field of services and industry, and this momentum produced many researches in the field of lean and its applications. In the past decade, several studies were conducted on lean manufacturing assessment LMA in general, given the wide range of lean application processes. These studies have assessed what has been achieved in the field of lean philosophy study, thus resulting in developing studies based on previous literature. Table 1 shows the previous studies on subjects directly related to the lean concept in general.
Based on Table 1, the number of papers reviewed, and the number of citation for each study, it seems that many studies have been conducted in the field of leans and these studies included a difference in the type of firms, processes, size of firms, different tools, differences in methodology. Nevertheless, these studies emphasize the importance of lean application and its role in improving performance. Regarding the subject of this paper, previous studies indicate that there is momentum in studies that include different assessments in terms of objectives, key words, definitions, objectives, firms, methodologies and results. Therefore, this paper summarizes a review of the research papers published in the time period from 2008 to 2017 that are directly related to the evaluation process and applications of lean practices. The structure of this study is as follows. The first section contains studies on the evaluation processes in general, followed by the second section, which includes the methodology of the study. The third section involves studies in addition to the analysis of the content of these studies. The fourth section includes the repetitive analysis of previous studies and the conclusions are discussed in the last section.  [8] 2000-2010 85 159 Lean Service [9] 1980-2008 92 Learning on Lean [10] 1980-2009 86 22 Lean Manufacturing [11] 2000-2011 48 52 Sustainability through Lean Construction Approach [12] 1992-2012 18 29 The lean gap [13] 1985-2012 38 47 Lean Manufacturing [14] 1988-2013 249 248 Lean Management [15] 1990-2013 66 185 lean manufacturing implementation [16] 1983-2013 43 102 lean manufacturing [17] 1990-2009 178 58 Lean Production [18] 1988-2011 546 151 Lean implementation [19] 1983-2014 148 47 Lean and green [20] 1998-2014 59 113 Lean and Sustainable Manufacturing [21] 2000-2014 58 21 Lean in healthcare [22] 2003-2013 243 135 Lean management [23] 2004-2014 49 10 Lean Assessment [24] 1970-2015 98 20 lean manufacturing, Six Sigma and Sustainability [25] 1990-2015 118 55 Lean Healthcare [26] 1983-2015 107 28 Lean and Six Sigma [27] 1999-2015 149 22 Lean Practices [28] 1974-2015 83 20 Six Sigma and Lean [29] 2000-2015 70 10 sustainability in supply chain management [30] 2000-2015 190 36

Methodology of the Study
The methodology of this study is based on the fundamentals of content analysis referred to in many studies such as [14,29,31] which included the following research steps: collection of materials, evaluating the appropriateness of subjects with each other and classification of what is selected in the classification lists (key words, scopes, objectives, and methodologies). Table 2 shows a brief explanation of the research methodology.

Collection of Materials
The general framework of this study is based on LMA studies, as LMA is considered a key basis for improving the performance of organizations in general, as indicated by many previous studies in the past decade the collection of data on the concept of lean in general. There are many studies that have been carried out in LMA in the previous decade, and these studies included the subject of LMA as a general subject and then dispersed in different parts. Tables 3-12 represent a wide range of these studies in LMA in general, and also include the number of citations for studies related to this research field.

Time Period 2008
The study found that there were 28 studies that included lean assessment methodology in general. Within the methodology of this study, the number was limited to research that includes the word lean as a keyword in the title. Therefore, the number was reduced to 12 papers. agency [33], Leanness measure, Data envelopment analysis and Slacks-based measure [34]; Lean production, Decision making and Strategic choices [35], Lean Manufacturing and Workplace [36], Lean production, Performance measurement and Balanced scorecard [37], Lean, Leanness, Fuzzy-logic leanness, Systematic measures and Benchmarking [38], Lean Manufacturing Systems and Performance Measurement [39], Lean strategy, Automotive supplier industry, Relationship building and Path analysis [40], Lean Thinking [41], Lean accounting, Contingency Theory, Performance measures, Management Control, Lean Manufacturing; Control and Interdependencies [42], Lean Bundles and Operational Performance [43]). It is noted that these studies included key words referring to practices in general, and some indicate performance, types of institutions and type of data.

Definitions, Methodology and Tools Classification
The studies [32][33][34][35][36][37][38][39][40][41][42][43] included a variety of methodologies: quantitative studies, qualitative studies, observations, and historical data, also the existence of fuzzy logic on a limited scale. One of the most important definitions in this time domain is that the definition of the Fuzzy logic for lean measurement: level of lean may include undetermined and uncertain degrees.

Time Period 2009
The study found that there were 25 studies that included lean assessment methodology in general, and within the methodology of this study, the number was limited to research that includes the word 'lean' as a keyword in the title. Therefore, the number was reduced to 8 papers.

Objective and Firm Classification
The previous studies [44][45][46][47][48][49][50][51] indicate to different objectives, including (Current state of lean practice, Identifying the practices that managers use to improve the overall manufacturing flexibility and including several types of institutions firms, such as electronic companies and financial services, whereas the companies included small-and medium-sized enterprises.

Definitions, Methodology and Tools Classification
The studies [44][45][46][47][48][49][50][51] included a variety of methodologies: quantitative studies, qualitative studies, observations and historical data, also the existence of fuzzy logic on a limited scale. One of the most important definitions in this time domain is that the definition of the Structural equation model (SEM) is estimated using data provided by companies.

Lean Tools Main Results References
Just-in-Time, Total Quality Management Results provide substantial evidence that utilization of non-financial manufacturing performance measures mediates the relationship between lean manufacturing and financial performance. [44] Counties Improvement, Just-in-Time, Total Quality Management, Value Stream Mapping Review of studies in benchmarking field. [45] Just-in-Time, Flexibility Identify practices that contribute to improving work through agility and softness.
[46] Techniques, and major groups involved in improving Flexibility The results identified the practices as the best practices that managers can use to improve processes. [47] General Practices Lean first, then Automate. [48] General Practices Select 14 key area: work processes, scheduling, inventory, equipment, layout, material handling, employees, quality, product design, suppliers, tools and techniques, customers, ergonomics and safety, and management and culture. [49] General Practices Determined 65 leans practices.
[50] General Practices Developing a model that contributes to improving training to use and apply lean skills. [51]

Time Period 2010
The study found that there were 33 studies that included lean assessment methodology in general, and within the methodology of this study, the number was limited to research that includes the word 'lean' as a keyword in the title. Therefore, the number was reduced to 16 papers.

Definitions, Methodology and Tools Classification
The studies [52][53][54][55][56][57][58][59][60][61][62][63][64][65][66][67] included a variety of methodologies: quantitative studies, qualitative studies, observations, historical data and a mathematical model. One of the most important definitions in this time domain is the definition of the Lean Kitting assembly as: "a specific collection of components and/or sub-assemblies together and combine with other kits to support one or more assembly operations for a given product".

Lean Tools Main Results References
Value stream mapping The process of lean application contributes to the disposal of waste in drills factories by reducing assembly and disposal of distances. [52] Just in Time, Perfect quality, Continuous improvement, Lean is considered an integrated system to improve the performance. [53]

References Visual management. Just in Time
The study showed the positive effect of adopting a lean methodology on the performance in companies. [54] 5S Simulations contribute to the strengthening of learning and training on lean assessment but do not give actual results to the lean level in companies in fact. [55] Value stream mapping The results indicate that there is a positive effect of lean in reducing time-related wastes and the number of operators according to the case study. [56] Value stream mapping The lean can have a significant impact on improving the operational processes. [57] Just in Time The results indicate that SMEs have a high potential to employ lean practices to improve the performance, raise production values, and eliminate waste. [58] Value stream mapping, Just in Time The results showed a high potential for improving the performance. [59] Total productive Maintenance, Total Quality Management, Value Stream Mapping and Visual Control.
The model includes uncertainty in the presence of waste. [60] Visual management, Value stream mapping, 5S and Line balancing The results indicate the effectiveness of lean practices in improving the service sector. [61] Value stream mapping Use simulations in training, education, and fact analysis.
[62] Operator walking distance and WIP Employing fuzzy logic in the decision-making process in improving the performance. [63] Lean practices Study the relation between lean and green supply chain. [66] Lean practices The study showed that there is an impact of the organizational change in the process of transition to lean. [67]

Time Period 2011
The study found that there were 24 studies that included lean assessment methodology in general, and within the methodology of this study, the number was limited to research that includes the word 'lean' as a keyword in the title. Therefore, the number is limited to 14 papers.

Definitions, Methodology and Tools Classification
The studies [68][69][70][71][72][73][74][75][76][77][78][79][80][81] included a variety of methodologies: quantitative studies, qualitative studies, observations, historical data and a mathematical model. One of the most important definitions in this time domain is that the definition of the Manufacturing Cells is characterized by the creation of a workflow in which the tasks are required and workers are closely connected in terms of time, space, and information. The proposed practices have contributed to the reduction of waste in the pharmaceutical industry specifically through value stream mapping. [73] Value Stream Mapping, Kanban, Contentious Improvement, Visual System and 5S The results were positive in reducing time and labor. [74] Total Quality Management and Lean Thinking The study showed the similarities between total quality and lean practices. [75] Just in Time, Kanban, Kaizen, Six Sigma, 5S, Value Stream Mapping, Results show that people need to have lean skills to ensure the quality and success of their application. [76] Teamwork and leadership, Continuous improvement, Standardized work, Pull production, Total Productive Maintenance, Visual, Management of production control, Visual management, Layout size and shape and Visibility and information exchange The study showed that there was a positive effect of lean practices on manufacturing cells. [77] Just in Time, Quality Systems, Work Teams, Cellular Manufacturing, Supplier Management Results showed that lean applications were still at their early stages. [78] Cycle time, Work in Processes and Labor Utilization Studies showed a strong correlation between practices used. [79] Lean Management System The prepared model shows positive results in improving the decision-making process. [80] Value Stream Mapping The prepared model shows positive results in improving the decision-making process. [81]

Time Period 2012
The study found that there were 27 studies that included lean assessment methodology in general. Within the methodology of this study, the number was limited to research that includes the word 'lean' as a keyword in the title. Therefore, the number was decreased to 16 papers.

Objective and Firm Classification
The objectives of previous studies [82][83][84][85][86][87][88][89][90][91][92][93][94][95][96][97] included Improving the decision-making process by determining the lean level within the application of hierarchical analysis, an exploratory study of the lean state of India's industries, developing a valuation model enables companies to understand the basic practices, rapid and accurate assessment of lean level, a broader understanding of how lean application in malaysia depends on supply chain management, developing a system of consulting companies towards the use and application of lean, developing a new methodology for lean assessment through variability source mapping, exploring lean in large companies, developing the assessment process within the ambiguous logic, the development of the decision-making system in lean applications. Several types of institutions firms were included, such as electronic companies petroleum drill bit manufacturing, hospitals, pharmaceutical industries and services sectors, and the size of companies included smalland medium-sized enterprises.

Definitions, Methodology and Tools Classification
The studies [82][83][84][85][86][87][88][89][90][91][92][93][94][95][96][97] included a variety of methodologies: quantitative studies, qualitative studies, observations, historical data and a mathematical model. One of the most important definitions in this time domain is that the definition of the Value stream mapping (VSM) is a lean manufacturing technical methodology that helps interpret the flow of materials and information currently needed to transfer goods or services to the end consumer.

Lean Tools
Main Results References Total productive maintenance, Employee's productivity and Total Productivity Management The study indicates to lean dimensions on operational performance. [82] Lean Manufacturing The results indicated that the proposed model improves the objectives of the manufacturing process (cost, quality, flexibility) [83] Lean Practices The results suggest that the evaluation and fuzzy logic analysis give more comprehensive results. [84] Just in time, Zero Defect, Pull, Continuous improvement Develop a proposed model to improve the effectiveness of lean application. [85] Continuous improvement, Zero Defect, Pull, Standardized Workplace, The results showed the effectiveness of the model. [86] Lean Practices Improving the level of operational performance does not depend only on lean. [87] Lean Manufacturing Develop a road map that contributes to the lean tracking of each stage of the production process and identify the difficulties faced by the lean application. [88] Continuous improvement, Setup time reduction, Product reliability and Product performance Results show a strong correlation between lean and quality management. [89] Lean Manufacturing Research study has provided a novel system for assessing the impact of lean manufacturing within SMEs. [90] Main Value Stream The results showed that the proposed model contributed to the identification of objects that have no value in production processes. [91] Kanban systems, Cellular manufacturing, Total productive maintenance, Process mapping, continuous improvement and 5S The study points to be deemed to be embracing Lean as an ideology. [92] Lean

Time Period 2013
The study found that there were 29 studies that included lean assessment methodology in general. Within the methodology of this study, the number was limited to research that includes the word 'lean' as a keyword in the title. Therefore, the number of paper was reduced to 11.

Objective and Firm Classification
The objectives of previous studies [98][99][100][101][102][103][104][105][106][107][108][109] included integration of lean and green strategies into the industrial system, describing a preliminary study in developing a conceptual model to measure leanness in manufacturing industry and purposing the relationship between competitive skills and lean manufacturing. It included several types of institutions firms.

Definitions, Methodology and Tools Classification
The studies [98][99][100][101][102][103][104][105][106][107][108][109] included a variety of methodologies: quantitative studies, qualitative studies, observations, historical data. One of the most important definitions in this time domain is that the definition of the Lean and Green is: the ability of operations to support the environmental management. The study identified seven basic dimensions to measure leanness. [99] Lean Manufacturing The study suggests that top management commitment, vendor participation, inventory management and quality improvement are important for Kanban deployment and towards lean manufacturing. [100] Lean Manufacturing There is a positive relationship between environmental management, operational performance, lean manufacturing, and human resources. [101] Value Stream, Pull, The basic results included the development of a simple tool to measure lean.
[102] Just in Time, Six Sigma, Total Quality Management Accounting and control practices management form the basis for a lean environment. [103] Lean Manufacturing Improve the effectiveness of measuring instruments [104] Just in Time, Work in Processes, Pull Comprehensive tool to evaluate services. [105] Lean Manufacturing The modeling and weighting of all the determinants in the lean tools is discussed in this paper. [106] Lean Manufacturing Proposed model for lean assessment [107] Lean Manufacturing The results indicate that companies that implement the lean system are able to develop quickly and at a lower cost. [108] Lean Manufacturing There is a positive correlation between competitive performance and lean system. [109]

Time Period 2014
The study found that there were 23 studies that included lean assessment methodology in general. In the methodology of this study, the number was limited to research that includes the word 'lean' as a keyword in the title. Therefore, the number was reduced to 14 papers.

Definitions, Methodology and Tools Classification
The studies [110][111][112][113][114][115][116][117][118][119][120][121][122][123] included a variety of methodologies: quantitative studies, qualitative studies, observations, historical data. One of the most important definitions in this time domain is that the definition of Resource-Based View (RBV) is used as a theoretical lens to examine the relationship between resources and lean practices and the operational performance.

Lean Tools Main Results References
Just in Time, Takt time, Defect rate. Proposing a comprehensive evaluation system that contributes to increasing the efficiency of the evaluation of firms. [110] Just in Time, Toyota Production System Cooperation between accounting and processes is needed to ensure a better application of lean. [111] Visual Management, Workplace Organization, 5S, Just in Time and Continuous Improvement, Total Quality Management and Total Productive Maintenance Early assessment to identify weaknesses contributes to higher efficiency for lean implementation. [112] Just in Time Results showed a difference in lean application levels in companies. [113]

Just in Time, Total Productive Maintenance and Work in Processes
Results indicate that the model contributes to decision making. [114]

Lean Practices, Just in Time
The results indicate that knowledge of cultural dimensions helps managers adapt lean practices [115] Value Stream Mapping, Work in Processes, 5S, Just in Time, and Continues Improvement Detecting the barriers to lean implementation in Indian companies. [116] Lean, Kaizen, Total Productivity Maintenance, Just In Time, Standardization, 5S The study showed the effectiveness of lean tools in raising productivity. [117] Just in Time, Value Stream Mapping, Total productive Management, Kaizen and Autonomation The results indicate that JIT and automation have the strongest significance on the operational performance. [118] Lean The results showed that the identification of the tracks for the implementation of the lean was very important. [119] Lean The proposed model can be used as benchmarks to improve the evaluation process. [120] Total Quality Management and Just and Time The results showed that the lean practices and manufacturing technologies have a unique effect on performance. [121] Value Stream Mapping, Pull and Just in Time The results indicate the importance of the skill of delivery on time as well as the relationship with suppliers. [122] Just in Time The results indicate the importance of customers in the success of lean. [123]

Time Period 2015
The study found that there were 26 studies that included lean assessment methodology in general. The methodology of this study was limited to research that includes the word 'lean' as a keyword in the title. Therefore, the number is restricted to 10 papers.

Lean Tools Main Results References
Just-in-Time Total Quality Management This study gives a new vision in applying Bayesian network for business performance. [124] Lean Manufacturing The study shows that production process measures are most related to lean. [

125] Lean Management
Organizational culture is essential for lean implementation.
[126] Lean Workforce development is important for lean implementation. [127] Value Stream Mapping, 5S, Pull and Six Sigma The study contributes to the development of a proposed model for the provision of services without waste. [128] Lean Manufacturing There is a strong relationship between empowerment and training. Identifying success factors is a key to success and improvement of companies. [130] Just in Time, Value Stream Mapping Design training courses or assess existing experiential learning courses. [131] Lean Practices It was established that the qualitative-based lean index is subjective quantitative types that lack scope. [132] Lean Practices Research contributes to identifying lean implementation strategies in India. [133]

Time Period 2016
The study found that there were 22 studies that included lean assessment methodology in general. In this study, the methodology was limited to the number of research that includes the word 'lean' as a keyword in the title. Therefore, the number is restricted to 14 papers.

Definitions, Methodology and Tools Classification
The studies [134][135][136][137][138][139][140][141][142][143][144][145][146][147] included a variety of methodologies: quantitative studies, qualitative studies, observations, historical data, mathematical model and fuzzy logic. One of the most important definitions in this time domain is that the definition Lean Manufacturing: is the set of practices intended to attain perfection in the identification and elimination of waste through continuous improvement flowing the product at the pull of the customer.

Lean Tools Main Results References
Lean, Six Sigma Results showed that the combination of lean and six sigma give results that are more effective than using lean only. [134] Lean Manufacturing Provide a lean assessment model that is more flexible. The results indicate the positive effect of lean on performance, and the results indicate that the most important obstacles are the limited knowledge of lean. [136] Just-in-Time, Kaizen, 5S, The results indicate that the most important practices are: operations, planning, human resources, customer relationship. [137] 5S, Value Stream Mapping, Continues Improvement, Teamwork, Visual control.
Total productive maintenance is identified as the most important lean practice. [138] Lean Manufacturing The results indicated that the lack of awareness and knowledge of staff is the most important obstacles to the implementation of lean. [

Time Period 2017
The study found 28 studies that included lean assessment methodology in general. Hence, the methodology of this study was limited to research that includes the word 'lean' as a keyword in the title. Therefore, only 10 papers were included.

Objective and Firm Classification
The main objectives of previous studies [148][149][150][151][152][153][154][155][156][157] were based on the studying the expected impact of soft practices on performance, improving the process of lean implementation and the improvement of the evaluation process .

Definitions, Methodology and Tools Classification
The studies [124][125][126][127][128][129][130][131][132][133][134] included a variety of methodologies: quantitative studies, qualitative studies, observations, historical data. One of the most important definitions in this time domain is that the definition of Lean is a manufacturing philosophy that shortens the time between the customer's order and the product build/shipment by eliminating the sources of wastes.

Lean Tools
Main Results References Flexible manpower, Pull system, Takt time, Continuous flow, Material supply, Zero defects, Quality assurance, Product / process quality planning, Standardized work, Production leveling, Maintenance system, Workplace organization, Goal oriented teams, Cross functional work, Problem solving methods, Improvement organization, Prioritization, Improvement approach The integration between lean and socio-technical and ergonomics contributes to the effectiveness of the organizational environment. [148] Value Stream Mapping This method has identified three levels of sustainability.
[149] Green paradigm is intended to reduce environmental risks and negative environmental impacts while improving the ecological efficiency and eliminating environmental waste in organizations chain initiatives.
Develop proposals to improve the supply chain [150] Takt time The results obtained in the three retailers are good enough to implement lean tools and enhance day to day efficiency at the outlets. [151] Lean Major barriers founded in micro, small and medium industries were lack of communication, attitude of shop floor management and degree of investment respectively. [143] Just-in-time production, Total productive maintenance, Cellular manufacturing, Total quality management The results of this study reinforce the assumption that during the implementation of lean production workforce development plays a key role due to its nature that advancement in the implementation translates to improving the performance. [154] Lean Manufacturing Proposals have been made to reduce waste in the cement industry. [155] Total quality control, Standardized operating procedures, Total production maintenance, Total quality control, Pull production / Kanban, Standardized operating procedures This study suggests that companies should implement more lean practices that affect some operational characteristics. [156] Process Improvement, The study indicates the importance of the lean and its active role in raising the level of performance. [157]

Digital Analysis of Previous Studies
This part of the study includes the digital analysis of previous studies and presents illustrations of the rules of metadata for the values of repetition.
Through the descriptive analysis of the methodology used in previous studies, the results are demonstrated as in Figure 1.  Through the descriptive analysis of studies that included references to performance in key words, objectives and results (Indicate For Performance, Not Indicate For Performance), the results are presented in Figure 3. Through the descriptive analysis of studies that included references to Just-in Time as a tool, the results are illustrated by Figure 4. The descriptive analysis for studies that included references to Value Stream Mapping is demonstrated by Figure 5. The descriptive analysis of studies that included references to (Fuzzy Logic) is showed by Figure 6. The descriptive analysis of studies that included references to Analytic Hierarchy Processes illustrate the results as in Figure 7.

Conclusion
Previous studies indicate several key points: a. There is a large amount of evaluation studies on lean practices. b. Extend areas of application of lean practices in various industry fields and services. c. Most of the objectives of the studies are to measure the lean level of enterprises and companies. d. Studies indicate the depth of the relationship as a power sector between performance and the level of lean. e. Studies indicate that there is no established methodology for measuring the level of lean practices. f. Some studies attempt to expand the fuzzy concept in the measurement of lean levels. g. Most studies are based on quantitative and qualitative methodologies. h. There are also studies based on qualitative data, and there are studies that combined the two methods in addition to multiple methods of arithmetic. There are many industries and sectors that need new and in-depth studies on lean studies, such as energy, tourism, hotel services, communications, and education. i. Studies that attempted to link the evaluation process to the practical decision-making process of the lean are often more related to mathematical logic and mathematical methods. j. In the past five years, there has been a clear change in evaluation methodology by combining quantitative and descriptive data with mathematical models that include calculations that help in decision making, and it was clear that the Analytic Hierarchy Process was the most commonly used.