HUMAN FACTORS ASSESSMENT. Thomas Koester (FORCE Technology, Denmark) Peter K. S rensen (FORCE Technology, Denmark)

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1 HUMAN FACTORS ASSESSMENT Thomas Koester (FORCE Technology, Denmark) Peter K. S rensen (FORCE Technology, Denmark) Abstract: There has since the development of simulator based maritime training been a demand for measurement of the effect of the training. Tools used to obtain these measures are often called assessment techniques. This paper will describe a repertoire of different assessment techniques. Some of these are well known and already in use. A special focus will be held on an in the maritime domain new and very promising methodology for measurement of crew stress. The methodology can if it is developed and refined be used as an assessment technique to evaluate the effect of Crew Resource Management training. The methodology will be used in the European project SPIN-HSV, and it is based on psycho physiological measurements of brain activity (EEG). The concluding recommendation is a composite use of different human factors parameters as indicators of increase in human performance (knowledge and skills) and a composite use of different methodologies for measurement of these parameters. 1. INTRODUCTION There has since the development of simulator based maritime training been a demand for measurement of the effect of the training and an answer to the question: Does the training really work? Is the knowledge and/or skills of participants improved during training or are they unchanged or even worse aggravated? Tools to investigate and answer these questions and used to obtain these measures are often called assessment techniques. This paper will describe a repertoire of different assessment techniques from subjective measures based on observations and questionnaires to objective measures based on psycho physiological techniques such as for example Heart Rate Variability or electric activity of the brain (EEG). Some of these are already in use. A special focus will be held on an in the maritime domain new and very promising methodology for measurement of crew stress. The methodology can if it is developed and refined be used as an assessment technique to evaluate the effect of the human factors oriented Crew Resource Management training. The methodology will be used in the European project SPIN-HSV, and it is based on psycho physiological measurements of brain activity (EEG). 2. TRAINING: DOES IT REALLY WORK? The purpose of maritime simulator based training is seen from the perspective of the student or participant the attainment of further knowledge and/or skills in various disciplines e.g. ship handling or Crew Resource Management. Assessment techniques are used to evaluate whether a goal is reached or not. The simulator is well suited for training of skills, but traditional assessment techniques from other learning contexts are usually designed for measurement of knowledge. Two measures are required in the evaluation of any kind of learning process: An initial measure and a concluding measure. The initial measure should be taken in the simulator immediately before training (but after familiarization with the simulator), and the concluding measure should be taken immediately after training. The results should be compared and tested for significance. The initial measure is used as a reference point to which the concluding measure can be compared. It is expected, that a comparison of the concluding measure and the initial measure show, that the level of knowledge and/or skill is significantly higher after training than before (see figure 1). The training has had no effect if the level is unchanged (see figure 2), and the effect has been negative if the concluding level of skill and/or knowledge is lower than the initial level (see figure 3). This type of measurement is called intervention study because the subject of the study is the effect of the intervention. In this case the intervention is training, but it could as well has been for example introduction of new procedures or new instruments or technology.

2 Initial measure Concluding measure 2.2 Confounding variables When we would like to evaluate the effect of training, the problem about confounding variables is always relevant (see figure 4). To eliminate the problems related to confounding variables we must ensure, that the training is the only intervention or influence the participants are subject to. We must be sure, that we use exactly the same test, exactly the same subjects and that all other variables than the training is eliminated. Fig. 1. The level of knowledge and/or skill is significantly higher after training than before. Training or confounding variables? Initial measure Concluding measure Initial measure Concluding measure Fig. 2. The training has had no effect if the level is unchanged. Fig. 4. Is the observed effect caused by training or confounding variables? One example could be experience. This is in particular a problem if the time distance between the initial measure and the concluding measure becomes too large. The initial measure should be taken immediately before training begins and the concluding measure should be taken immediately after the training is finished. Otherwise it is impossible to determine if a change in performance is due to general increase in experience or due to the training. Another example could be a mixture of training and increased salary. If salary were increased it could lead to increase of motivation and thereby better performance. Initial measure Concluding measure Fig. 3. The effect of the training has been negative if the concluding level of skill and/or knowledge is lower than the initial level. 2.1 Significance Test for significance is done according to standard procedures. If the results are found to be insignificant, no conclusions about the effect of the training can be drawn. The obtained results could be purely random fluctuations. 2.3 The principle of composite use of methods The overall quality of the assessment especially the validity can be enhanced by composite use of methodologies. The methods described in this paper covers a variety of methodologies from subjective measures based on observations and questionnaires to objective measures based on psycho physiological techniques such as for example Heart Rate Variability or electric activity of the brain (EEG). Corresponding to that, the human factors parameters suggested as indicators of improved performance (improved knowledge and skills) also covers a wide selection, for example mental workload, situation awareness, stress and fatigue.

3 It is most likely, that the principle of composite use of methods could emerge to be a very powerful assessment tool for evaluation of the effect of maritime simulator based training. If for example the effect of Crew Resource Management training is examined, more than one parameter should be used as indicator, and each of these parameters should be measured by means of more than one method or technique. 3. ASSESSMENT IN COMPUTER BASED TRAINING (CBT) Traditional examination oral or written of students will reveal improvements in knowledge, but it is not suitable for evaluation of skills. This type of evaluation technique can be used with great advantage in Computer Based Training programmes (see figure 5), but it will have very limited success within simulator-based training. Fig. 5. Equipment for Computer Based Training. The picture shows the set up for SimFlex Radar ARPA Courseware from FORCE Technology. the SimFlex COLREG Courseware system from FORCE Technology (see figure 6). The student is in this system asked questions in the syllabus of learning material. The student responds with answers in a multiple-choice style. The answers are compared to a key, and the number of correct answers is calculated. The examination is not a true evaluation of the obtained knowledge since there is no initial measure, but the same method could be used for initial measurement. In this case the method could be used as an assessment technique. 4. INSTRUCTOR RATING The traditional technique for measurement of skills is often called instructor rating. This technique is used in simulator-based cadet training at Force Technology, Division for Maritime Industry (DMI) (see [1] for further description). The technique is based on subjective rating made by one or more instructors. The reliability and especially the validity of this method can be discussed due to its elements of subjectivity. The scale used for measurement is independent from level of difficulty. The same rating given both as initial and concluding rating will therefore represent an improvement of performance due to the increase in level of difficulty from initial to concluding evaluation. This is, however, in contradiction to the principle that the conditions of evaluation should be kept unchanged, i.e. that the same test should be used for both initial and concluding evaluation for purposes of comparison. The instructor rating is based on observations of the communication and behaviour of the participating crew. These observations will normally be audio visual (perhaps mediated through devices such as a video camera) and they will be supported by build in systems for registration of the participants use of instruments, knobs and handles for the control of the vessel the so called replay system in the simulator. Fig. 6. An example from the syllabus of learning material from the SimFlex COLREG Courseware system from FORCE Technology. An example of examination used as assessment technique in Computer Based Training is found in Even though the instructor rating is partly subjective and the reliability and validity can be questioned, it is still one of the most often used and most straightforward ways of measuring the participant performance (e.g. ship handling and Crew Resource Management performance) in the maritime simulator. The instructor rating methodology is well suited as instrument used as an assessment technique for the purpose of evaluation of the effect of simulator based training such as ship handling or basic navigation and watch keeping skills (e.g. the training of cadets, see [1] for further description), but it is not well suited as

4 stand alone method for evaluation of the effect of Crew Resource Management training programmes due to the complexity of Crew Resource Management skills. We can conclude, that the training has served its purpose if and only if the result obtained by the instructor rating technique shows a significant improvement from initial to concluding test. 5. OBSERVATION OF COMMUNICATION A special focus in observation of communication can be used as an assessment technique for evaluation of improvements in the safety of crew performance. The focus is on the time perspective, the tense in the communication. The underlying assumption is, that a crew communicating in future tense and about events in the future will be less exposed to accidents and incidents and less vulnerable than a crew communicating in present or past tense [2]. The reason for this is probably better anticipation, better planning and higher degree of preparedness. When this method is applied in the maritime simulator it is often done in that way, that an observer (e.g. instructor or psychologist) is recording communication sequences in a spreadsheet on a personal computer. This recording of communication is when it is done in real time subject to errors, and the subjectivity creates some doubt about reliability and validity. The recording can be done post hoc by use of video recordings. This will probably enhance the quality and reliability. Used as an assessment technique the tense element of communication can be used for evaluation of the effect of Crew Resource Management training. The effect would be, that the communication would change from initial being mostly past or present tense to a concluding situation of a dominating majority of future tense communication (see figure 7). 100% 75% 50% 25% 0% Initial Concluding Future Present Past Fig. 7. The communication has improved and we can conclude, that the Crew Resource Management training has served its purpose. If the compound of communication is unchanged (or insignificantly changed) from initial to concluding measure, we will say, that the training have had no effect what so ever (see figure 8). 100% 75% 50% 25% 0% Initial Concluding Future Present Past Fig. 8. The possible very small improvement of communication is not significant, and we are not able to conclude, that the Crew Resource Management training has served its purpose. 6. QUESTIONNAIRE BASED TECHNIQUES FOR MEASUREMENT OF SITUATION AWARENESS Situation awareness is according to Endsley [3] the ability to perceive information from and about the surrounding environment (e.g. visual information from looking through the window of the wheel house, information from instruments, radar etc., information communicated from other crew members or through radio), the ability to comprehend this information and the ability to anticipate future events on the basis of these information. The ability to perceive elements in the current situation (situation awareness level 1), comprehend the current situation (situation awareness level 2) and make projections of future events (situation awareness level 3) is very important in the everyday routine work on board ships of any type. Together the perception, comprehension and projection form the situation awareness of the operator, the crewmember. The situation awareness is important in the navigation of the vessel, the anti collision work and in the maintenance of a safe and efficient operation of the vessel in any matter. It is possible to find evidence from maritime accident reports, that a lack of situation awareness can actually cause accidents or contribute significantly to the causal development of them. According to a study performed by Grech & Horberry [4] 71% of all human error types on ships are situation awareness related problems. It is therefore evident, that proper situation awareness has significant effect on the overall safety of any type of maritime vessel and that a lack of situation awareness eventually can cause

5 accidents such as groundings, collisions or structural damage to the vessel [5]. Situation awareness is not always directly subject to training in simulator based training programmes, but it is certainly a very important element in Crew Resource Management training. The result of such training should definitely be enhanced or improved situation awareness - both from the perspective of the single crewmember and from the perspective of the entire crew. Crew or team situation awareness is build from good communication and proper sharing of information, which again is a basic Crew Resource Management skill. An evaluation of situation awareness could therefore act as an assessment technique for determination of the effect of a Crew Resource Management training programme. A number of methods for measurement of situation awareness have been suggested in the literature. One of them is the SAGAT methodology [6]. This methodology which is originally designed for the purpose of testing airplane pilots in flight simulators is based on questionnaires, which is supposed to test the situation awareness in a given moment in time. The work performed by the operator, the pilot, officer on watch etc. has to be interrupted or abandoned when the questionnaires are filled in. This is perfectly possible in a simulated environment where the simulation can be momentarily stopped, but it could be a threat to the safety if this method is used in real environments. The method will simply generate a loss of situation awareness. Further, the method is suitable for single measurements of situation awareness, but it is not suitable for continuous monitoring of situation awareness over longer periods of time [5]. The SAGAT methodology is well suited as instrument used as an assessment technique for the purpose of evaluation of the effect of a simulator based Crew Resource Management programme. We can conclude, that the training has served its purpose if and only if the result obtained by the methodology shows a significant improvement in situation awareness from initial to concluding test. 7. QUESTIONNAIRE BASED TECHNIQUES FOR MEASUREMENT OF MENTAL WORKLOAD Another important skill enhanced from Crew Resource Management training apart from situation awareness is the ability to manage mental workload and the ability to adjust behaviour and crew communication to the level of workload in the given situation whether this is high or low. The ability to cope with mental workload can be tested through psycho physiological methods, which are described later in this paper, through behavioural measures and through questionnaire based subjective methods such as the NASA-Task-Load Index (NASA-TLX) [7]. The subjective questionnaire based techniques (like the NASA-TLX methodology) for measurement of mental workload are well suited as assessment techniques for the purpose of evaluation of the effect of a simulator based Crew Resource Management programme. We can conclude, that the training has served its purpose if and only if the result obtained by the methodology shows a significant decrease in subjective (perceived) mental workload from initial to concluding test due to improved workload management skills. 8. PSYCHO PHYSIOLOGICAL MEASUREMENT Psycho physiological measurements are primarily used for measurement of four human factors variables: 1. Workload 2. Visual attention 3. Fatigue 4. Stress The methods are general, but they can be used for assessment purposes as well. They are particular well suited for evaluation of the effect of human factors training or Crew Resource Management training. The disadvantage compared to for example instructor rating, observation of communication and questionnaire-based methods is, that psycho physiological methods require advanced and often expensive equipment. But the cost of the psycho physiological equipment is, when it is compared to the total cost of a full mission simulator, insignificant. The most important available techniques are: Galvanic Skin Response (GSR) Heart Rate Variability (HRV), electrocardiography (EKG/ECG) Ocular activity, blink rate and eye movement detection Electric activity of the brain, electroencephalography (EEG) See [8] for further details on psycho physiological measurement. 8.1 Galvanic Skin Response (GSR) Galvanic Skin Response is an electrical measure of sweat (perspiration), usually measured with electrodes in the hand. The signals from the electrodes are amplified and the results are recorded electronically. The underlying assumption is that

6 stress will induce activity of sweat glands, and that the sweat response to stress is very immediate. This technique is well known from lie detectors. If we assume, that inexperience, poor workload management and poor Crew Resource Management skills are likely to cause stress, a test of stress could be used as assessment technique for Crew Resource Management programmes. We can conclude, that the training has served its purpose if and only if the result obtained by the methodology shows a significant decrease in level of stress from initial to concluding test. 8.2 Heart Rate Variability (HRV), electrocardiography (EKG/ECG) Heart Rate Variability is an electrical measure done with electrodes placed on limbs and/or torso. The signals from the electrodes are amplified and the results are recorded electronically. The so-called 0.1 Hz component or band is especially sensitive to workload (see [9], p. 28) and is often used as a direct measure of workload. One example is the measurement of maritime pilots approaching the harbour of Rotterdam done by Westrenen [9]. Psycho physiological measurements of Heart Rate Variability (the 0.1 Hz band) can alone or together with subjective questionnaire based techniques (like the NASA-TLX methodology) be used for measurement of mental workload, and are therefore well suited as instruments for assessment of the effect of a simulator based Crew Resource Management programme. We can conclude, that the training has served its purpose if and only if the result obtained by the methodology shows a significant decrease in measured mental workload from initial to concluding test due to improved workload management skills. 8.3 Ocular activity, blink rate and eye movement detection Ocular activity, blink rate and eye movement are usually measured with equipment based on video recording of the position of the pupil. The video signals are analysed and interpreted automatically by a computer, and the results are presented through a user interface. This type of measurement can be used for evaluation of fatigue [10], but it can also be used for evaluation and quantification of visual attention. It is, from the output of eye movement detection equipment possible to directly determine exactly what the subject is gazing at e.g. which instrument or which feature in the surrounding environment outside the wheelhouse. This measure of visual attention can if it is compared to and analysed and evaluated against a certain required performance standard be used as an indication of crew performance. Used as an assessment technique an increase in performance indicated by improved visual attention should be observed from the initial to the concluding observation. If we assume, that inexperience, poor workload management and poor Crew Resource Management skills are likely to cause fatigue, a test of fatigue could be used as assessment technique for Crew Resource Management programmes. Fatigue can be measured with a variety of psycho physiological tests e.g. ocular measurements (as just described) or EEG [10]. We can conclude, that the training has served its purpose if and only if the result obtained by the methodology shows a significant decrease in exposure to fatigue from initial to concluding test. However, the problem about using measurements of fatigue is, that the influence of confounding variables such as time of day, lack of sleep and jetlag is particular large compared to other human factor variables e.g. workload and stress. If the measure is used, one must be sure that the underlying, residual level of fatigue is the same at the beginning of both (initial and concluding) tests, that the time of the day the tests are performed is exactly the same and that the duration of the test is exactly the same. Further, the tests must be at exactly the same level of difficulty. These countermeasures will neutralise the effect of confounding variables. It will, however, always be a problem, that it is impossible to control the sleep quality of the participants. Even though they have gained the same amount of sleep in terms of hours slept, the quality of this sleep could be very different due to a number of influencing factors Initial Fatigue start Concluding Fatigue end Fig. 9. This diagram shows the level of fatigue at the start of a simulator voyage and again in the end of the simulator voyage for both initial and concluding measure.

7 The schematic diagram in figure 9 shows the level of fatigue at the start of a simulator voyage and again in the end of the simulator voyage for both initial and concluding measure. We can conclude, that there is an improvement from initial to concluding test when, and only when the level of fatigue obtained during the voyage is significantly lower in the concluding test than in the initial test. 8.4 Electric activity of the brain, electroencephalography (EEG) Measurement of electric activity of the brain, electroencephalogram (EEG), can be used for evaluation of a variety of psycho physiological and psychological variables or parameters. As just mentioned, EEG can be used for measurement of fatigue [10], but it can also be used for measurement of overall level of vigilance or alertness, level of psychological or cognitive activity or level of stress. See [8] and [11] for further details on measurement of EEG. Fig. 11. The Nervus Monitor Trolley EEG is measured by means of electrodes placed directly on the skin on the scull after certain predefined principles and standards e.g. the international electrode system (see [8], p ). The signals from the electrodes are amplified and the results are recorded electronically by means of analog or digital equipment. An example of an amplifier (The Nervus U16 Amplifier) is shown in figure 10, and example of recording equipment is shown in figure 11 and 12. Fig. 12. The Nervus Monitor screen The results are interpreted with respect to the stateof-the-art knowledge about how levels of stress and mental activity are reflected in different patters of EEG data (see for example [11]). Fig. 10. The Nervus U16 Amplifier If we again assume, that inexperience, poor workload management and poor Crew Resource Management skills are likely to cause stress, an EEG based test of level of stress could be used as assessment technique for Crew Resource Management programmes. We can conclude, that the training has served its purpose if and only if the result obtained by the methodology shows a decrease in level of stress from initial to concluding test. It is to eliminate the effect of confounding variables important to ensure, that the tests used initially and concluding both are at exactly the same level of difficulty and therefore would be expected to generate exactly the same level of stress if no intervention in the form of training had been given.

8 It is at the moment of the writing of this paper (April 2003) not possible to find any examples in the literature of application of EEG techniques for measurement of stress levels in maritime crews. However, a number of examples of the application of other psycho physiological methods in the maritime domain e.g. Heart Rate Variability can be found (for example [9]). Examples of use of EEG technology in aviation and flight simulators can be found as well (see for example [12]). The use of EEG techniques is particular interesting and promising because they represent very objective and accurate means of measurement of internal (not directly observable) mental activity of the crew. EEG measurement is therefore likely to produce more valid and reliable measures of certain human factors parameters than the more subjective methodologies based on observations and questionnaires. It is therefore relevant on the basis of the great potential of EEG methodologies with respect to assessment techniques in maritime simulator based training to describe the application of EEG methodologies in the SPIN-HSV project. It is important to notice, that the use of EEG methodologies in the SPIN-HSV project not is with assessment as the purpose. But since the introduction of EEG based measurement in the maritime domain is new, any experience from the application of the methodology will be of relevance and interest to the maritime human factors community. If the technique in itself is mastered, the application as assessment tool is pretty close. 9. THE USE OF EEG AS MEASURE OF LEVEL OF STRESS IN THE SPIN-HSV PROJECT SPIN-HSV is a collaborative Research & Technology Development project under the 5 th Framework Programme of the European Union. The full title of the project is Shipping quality and Safety of high-speed vessels, terminals and Ports operations In Nodal points. The objective is assessment of procedures, technologies and existing policies aiming to optimise high speed shipping, and the interface between vessels and terminals and to improve quality shipping. One point of focus in the project is the experimental quantification of human factors parameters such as mental workload, fatigue and stress levels in normal high-speed vessel operation and the quantification of variations in these parameters during the voyage and time in harbour. The experiments will be designed as laboratory experiments with use of a maritime full mission simulator as the laboratory and setting. The parameters will be quantified by means of observational and questionnaire based methods (e.g. instructor rating, observation of communication and SAGAT and NASA-TLX like methodologies), and the use of psycho physiological recoding methods of brain activity (EEG) will be introduced as a measure of stress levels and overall mental activity of the crew. The subjects used in the experiment are both inexperienced cadet students and experienced HSV crews. The experienced subjects will sail well-known vessels in well-known environments (routes) and well-known vessels in new environments (routes). The validity of the methodology will be tested two fold: 1. By use of composite measures collected with questionnaire based methodologies and psycho physiological measurement of Galvanic Skin Response. 2. By control measures made as a field study on an equivalent vessel servicing an equivalent route. The use of composite measures will support the internal validity and helps us answer the question: Are we really measuring the level of stress? The use of control measures will support the external validity and helps us answer the question: Can we generalise from our findings to the real world outside the simulator (the laboratory)? 10. CONCLUSION As described in the beginning of this paper, it is possible to enhance the overall quality of the assessment especially the validity by composite use of methodologies. The methods described in this paper covers a variety of methodologies from subjective measures based on observations and questionnaires to objective measures based on psycho physiological techniques such as for example Heart Rate Variability or electric activity of the brain (EEG). Corresponding to that, the human factors parameters suggested as indicators of improved performance (improved knowledge and skills) also covers a wide selection, for example mental workload, situation awareness, stress and fatigue. The principle of composite use of methods could therefore emerge to be a very powerful assessment tool for evaluation of the effect of maritime simulator based training. If for example the effect of Crew Resource Management training is examined, more than one parameter should be used as indicator (e.g. mental workload and stress), and each of these parameters should be measured by means of more than one method or technique (e.g. mental workload measured by NASA-TLX questionnaire and Heart

9 Rate Variability and stress measured by Galvanic Skin Response and EEG). REFERENCES [1] Rabjerg, C.T. & Smyth, R. (2003). A UNIQUE CONCEPT FOR SIMULATOR BASED CADET TRAINING. Submitted for: MARSIM 03, Kanazawa, Japan, August 25-28, [2] Andersen, P.B. (1998). Analysis of Maritime Operations II, Analysis. Center for Human-Machine Interaction. Report CHMI , p. 64 ( [3] Endsley, M.R. (2000a). Theoretical Underpinnings of Situation Awareness: A Critical Review. In M.R. Endsley & D.J. Garland (Ed.), Situation Awareness Analysis and Measurement (pp. 3-32). Mahwah, New Jersey: Lawrence Erlbaum Associates. [4] Grech, M. & Horberry, T. (2002). Human Error in Maritime Operations: Situation Awareness and Accident Reports. 5th International Workshop on Human Error, Safety and Systems Development June 2002, Noah s On The Beach, Newcastle, Australia. (pp ) Mahwah, New Jersey: Lawrence Erlbaum Associates, Publishers. [11] Fisch, B.J. (1999). Fisch & Spehlmann s EEG Primer (3. rev. ed.). Amsterdam: Elsevier. [12] NASA Langley Research Center, March 11, Task 3. Physiological Factors ( ). Document published and available on the Internet. Physiological/PF.html AUTHOR S BIOGRAPHY Thomas Koester, psychologist, MA. 2_ years of experience as human factors expert (within the maritime domain, offshore industry, power plants and the medical domain) at FORCE Technology, Division for Maritime Industry (DMI). Peter K. S rensen, shipmaster, B.Sc.Eng. 10 years of seagoing experience and 9 years seniority at FORCE Technology, Division for Maritime Industry (DMI) as instructor, navigation advisor and manager. [5] Koester, T. (2003). Situation Awareness and Situation Dependent Behaviour Adjustment in the Maritime Work Domain. Submitted for the 10 th International Conference on Human Computer Interaction (HCI International 2003), Crete, Greece, June 22-27, [6] Endsley, M.R. (2000b). Direct Measurement of Situation Awareness: Validity and Use of SAGAT. In M.R. Endsley & D.J. Garland (Ed.), Situation Awareness Analysis and Measurement (pp ). Mahwah, New Jersey: Lawrence Erlbaum Associates. [7] Hilburn, B. & Jorna, P.G.A.M. (2001). Workload and Air Traffic Control. In Hancock, P.A. & Desmund, P.A. (Ed.), Stress, Workload and Fatigue (pp ). Mahwah, New Jersey: Lawrence Erlbaum Associates, Publishers. [8] Stern, R.M., Ray, W.J. & Quigley, K.S. (2001). Psychophysiological Recording (2.ed.). Oxford: Oxford University Press. [9] Van Westrenen, F. (1999). The Maritime Pilot at Work. Delft: Uitgeverij Eburon. [10] Rau, P.S. (2001). A Heavy Vehicle Drowsy Driver Detection and Warning System: Scientific Issues and Technical Challenges. In Hancock, P.A. & Desmund, P.A. (Ed.), Stress, Workload and Fatigue