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CHAPTER 3 METHODOLOGY
This chapter provides a detailed account of the development of the Mental Workload Index, which is the essence of this study. The chosen development approach and process is motivated and discussed after which a description of the specific steps that were followed to identify the factors to be included in the index and the allocation of weights to those factors, are detailed.
DEVELOPMENT APPROACH
The guiding principle in the approach was to develop a methodology that would provide an objective measurement of the ‘pure’, task-related mental workload factors that may be imposed on TCOs at specific train control centres. The methodology deliberately steers clear of assessing the performance of operators or the workload as subjectively experienced by specific train control operators.
However, because tasks are executed by human operators, it is difficult to isolate the individual from the task. Every attempt was made to adhere to the premise of identifying and measuring the task-related factors in the research design and in the development of the mental workload index.
A combination of quantitative and qualitative techniques was used in order to achieve the objectives of the study. The techniques include psychological and operational research techniques and physiological measurements.
For the proposed methodology to be successfully implemented and accepted by all relevant role players at Spoornet it was essential that they all formed part of the development process.
RATIONALE FOR THE METHODOLOGY
The model of Meshkati (1988) provides no guidelines as to which specific measurement techniques should be used for validation of mental workload in a context similar to that of this study. This lack of clarity as well as the lack of information on tasks and simulated environments in existing research, as confirmed by Cilliers (1992), as well as the conflicting research results referred to earlier, has lead to a problematic situation in the rail operational environment. The uncertainty and therefore the risk of using measurement techniques as described in the literature and then applying them to the context of rail safety, where operational decisions would be based on these measurements, is too high. It has therefore become necessary to mitigate the existing risk by exploring new ways of measuring mental workload.
It was decided that in the absence of a precedent or clear guidelines for a valid and reliable measurement technique, a new technique should be developed which will meet the criteria as stated in the literature. Considering the operational environment in which the results of this study may be applied, it was decided to pursue a participative and transparent development process that would allow for buy-in and high acceptance by the users of the system. These conditions were important as it will be operational managers, not mental workload specialists, who will use the tool to assist them to make operational decisions that relate to human factors and human performance. The following were the criteria to be met by the Mental Work Load Index (MWLI) measurement method:
Construct validity was especially important because the process had to actually measure the factor mental workload and not another factor such as fatigue, which could be incorrectly perceived to be mental workload.
The predictive validity of the measurement technique for mental workload was also important as the mental workload measurement technique had to assess and/or predict the stress that the mental workload of a particular section could create for TCOs controlling that section.
Other criteria which it was considered important for the methodology to comply with were:
• Non-intrusiveness: TCOs perform safety-critical tasks and the method used may not distract them or affect their performance while executing their tasks.
• Operator and user acceptance.
• Sensitivity: the method should detect changes or differences in the mental workload imposed.
• Implementation requirements and affordability: the method should be easy to learn and administer, be portable and once developed, should be inexpensive to implement and maintain.
Although the primary objective of this project was the objective measurement of mental workload, there are other important aspects that had to be considered and that were related to the methodology for developing such a measure. An important envisaged benefit of the methodology is that it will be a scientifically developed process that could be defended should a legal, industrial relations or operational safety dispute arise with regard to the mental workload of TCOs in train control centres.
It must be borne in mind that the envisaged methodology is primarily aimed at determining the content of tasks and the mental workload demands these may place on operators. The mental workload should not be confused with on-the-job performance of the operators, which is a function of mental and physical workload combined with factors such as motivation, alertness, physical health and mental wellbeing.
In summary, the aim of the envisaged methodology is to create a management tool that can be applied to classify different railway lines and sections in terms of the mental workload they will impose on operators. Such classification will in turn facilitate planning and the allocation of resources to ensure safe train control practices and operations.
CHAPTER 1: INTRODUCTION
1.1 PROBLEM STATEMENT
1.2 BACKGROUND
1.3 RESEARCH GAP
1.4 JUSTIFICATION FOR THE STUDY
1.5 AIMS OF THE RESEARCH
1.6 HYPOTHESIS AND RESEARCH QUESTIONS
1.7 OUTLINE OF THE THESIS
CHAPTER 2: LITERATURE STUDY
2.1 THE DEFINITION AND DESCRIPTION OF MENTAL WORKLOAD
2.2 MENTAL WORKLOAD AS RELATED TO OTHER OPERATOR STATES
2.3 AN OPERATIONAL DEFINITION OF MENTAL WORKLOAD
2.4 VARIABLES THAT INFLUENCE MENTAL WORKLOAD
2.5 APPLICATION OF WORKLOAD THEORY
2.6 AN OVERVIEW OF MENTAL WORKLOAD MEASUREMENT TECHNIQUES
2.7 CRITERIA FOR THE SELECTION OF MENTAL WORKLOAD ASSESSMENT TECHNIQUES
2.8 DETAILED DISCUSSION OF MENTAL WORKLOAD ASSESSMENT TECHNIQUES
2.9 CONTEXTUALISATION OF THE STUDY
CHAPTER 3: METHODOLOGY
3.1 DEVELOPMENT APPROACH
3.2 RATIONALE FOR THE METHODOLOGY
3.3 SUMMARY OF DEVELOPMENT PROCESS
3.4 STEPS IN DEVELOPMENT PROCESS AND ASSOCIATED INSTRUMENTS
3.5 DETAILED DESCRIPTION OF THE DEVELOPMENT PROCESS
3.6 DEVELOPMENT OF THE MENTAL WORKLOAD MODEL
3.7 IDENTIFICATION OF TASK AND MODERATING FACTORS
3.8 DEFINITION OF TASK AND MODERATING FACTORS
3.9 ALLOCATION OF WEIGHTS AND QUANTIFICATION OF MODERATORS
3.10 CALCULATION OF THE MENTAL WORKLOAD INDEX
3.11 CONCLUDING COMMENTS
CHAPTER 4: RESULTS
4.1 CORRELATING THE MENTAL WORKLOAD INDEX WITH PSYCHOPHYSIOLOGICAL PARAMETERS
4.2 THE VERIFICATION STUDY
4.3 MEASUREMENT TECHNIQUES AND METHODOLOGY
4.4 DATA ANALYSIS APPROACH
4.5 RESULTS OF THE VERIFICATION STUDY
4.6 SENSITIVITY ANALYSIS AND OPTIMISATION OF THE MENTAL WORKLOAD INDEX
4.7 SUMMARY OF RESULTS
5. DISCUSSION
5.1 HYPOTHESIS AND RESEARCH QUESTIONS
5.2 CRITICAL EVALUATION OF THE CONTRIBUTION OF THE MENTAL WORKLOAD INDEX
5.3 APPLICATION AND IMPLEMENTATION OF THE MENTAL WORKLOAD INDEX
5.4 APPLICATION OF A CRITICAL MENTAL WORKLOAD LEVEL
CHAPTER 6: CONCLUSIONS
6.1 SUMMARY AND CONCLUDING REMARKS
6.2 LIMITATIONS OF THE STUDY
6.3 RECOMMENDATIONS
REFERENCES
APPENDICES
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