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Motamedzade M, Abbasinia M, Parvari R, Oliaie M, Karimi S, Mohammadi P. Mental workload and its association with fatigue in operating room personnel of Hamadan hospitals, Iran, 2016. JOHE. 2017; 6 (2) :98-105
URL: http://johe.rums.ac.ir/article-1-249-en.html
1- Professor Dept. of Ergonomics, School of Public Health, Hamadan University of Medical Sciences, Hamadan, Iran.
2- PhD Student in Occupational Health Dept. of Occupational Health, School of Public Health, Hamadan University of Medical Sciences, Hamadan, Iran.
3- MSc Student in Occupational Health Dept. of Occupational Health, School of Public Health, Hamadan University of Medical Sciences, Hamadan, Iran.
4- PhD Student in Occupational Health Dept. of Occupational Health, School of Public Health, Hamadan University of Medical Sciences, Hamadan, Iran. , pmohammadi64@gmail.com
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Mental workload and its association with fatigue in operating room personnel of Hamadan hospitals, Iran, 2016
 
Motamedzade M, PhD1, Abbasinia M, MSc2, Parvari R, MSc2, Oliaie M, MSc2, Karimi S, BSc3, Mohammadi P, MSc2*

1- Professor, Dept. of Ergonomics, School of Public Health, Hamadan University of Medical Sciences, Hamadan, Iran. 2- PhD Student in Occupational Health, Dept. of Occupational Health, School of Public Health, Hamadan University of Medical Sciences, Hamadan, Iran. 3-MSc Student in Occupational Health, Dept. of Occupational Health, School of Public Health, Hamadan University of Medical Sciences, Hamadan, Iran.
 
Abstract                                                                                                 Received: May 2017, Accepted: July 2017
Background: Fatigue in the workers reduces the individual's resistance and eventually leads to the lower performance, increased errors and accidents. This study assessed the fatigue, mental workload and the correlation between them, in operating room personnel of Hamadan hospitals, Iran.
Materials and Methods: In a descriptive study, the mental workload and its association with fatigue in operating room personnel were investigated. Total of 188 cases including surgeons, nurses, operating room and anesthesia technicians participated in the study. Data were collected using demographic, fatigue and mental workload questionnaires, and were analyzed using SPSS software.
Results: The mean of overall mental workload was 74.3 ± 10.8. The results also showed that overall fatigue and its domains, including subjective fatigue, concentration, motivation and physical activity were 48.73%, 54.31%, 51.65%, 38.96% and 42.06%, respectively. Among different domains of mental workload, performance (r = -0.380, P < 0.001) and frustration (r = 0.222, P = 0.014) were significantly associated with overall fatigue. Between overall mental workload and overall fatigue, there was not a significant correlation (r = 0.029, P = 0.749). Among different dimensions of fatigue, only subjective fatigue was correlated with mental workload (r = 0.255, P = 0. 005).
Conclusions: Regarding the association of performance and the frustration with overall fatigue and the association of overall mental workload with subjective fatigue, it can be concluded that mental workload and fatigue may be correlated with each other. Therefore, any reduction in mental workload domains may lead to fatigue reduction in the operating room personnel.

Keywords: Workload, Fatigue, Operating Room, Personnel, Questionnaire

 
Introduction
Fatigue is defined as a temporary loss of energy and strength, resulting from hard or long time physical or mental work and usually results in performance decrement. This occurs when the body cannot provide enough energy to perform a task. The depletion of energy increases muscle fatigue to the point whereby physical or mental activity cannot be performed (1-3). Eventually, tired people may do their normal work procedures with error. Generally, fatigue may cause a feeling of contusion, decreased physical function, autonomic nervous system imbalance, and reduced work efficiency. Tired people are also more likely to choose risky behaviors such as taking shortcut routes to carry out their tasks (4-6).
Job dissatisfaction, mild mental disorders, lack of sleep and workload are mentioned in literature as fatigue risk factors in the job (7, 8). Higher workload, the existence of fatigue and inappropriate working time schedule, lead to lower efficiency and loss of memory, impaired thinking processes, irritability and reduced learning (9). For example, high levels of the workload in the laparoscopic task as a medical job have resulted in decreased performance (10).
There are several ways to measure workload. A simple method to measure the workload is a subjective method. According to this method, if a person feels heavy workload so the workload is categorized as high (11). Although physiological measurements are more accurate, subjective methods are more practical (12). Multidimensional methods are the most common and accepted subjective methods to measure mental workload. National Aeronautics and Space Administration-Task Load Index (NASA-TLX) is a good multi-dimensional scale for measuring mental workload, very sensitive to changes in workload and also has a high level of diagnosticity (13-15). There is not a direct way to measure fatigue. However, fatigue can be measured from its consequences and symptoms or from the physiological or psychological indications associated with the symptoms of fatigue (16).
Healthcare professions are of high sensitivity in nature due to concerns around patient’s safety in the hospitals, increasing probability of human errors in tired personnel as well as and weak psychomotor and cognitive performance. (17, 18). Moreover, the increased workload can increase job pressures and cause difficulties in the decision making process in the healthcare personnel. Among the healthcare personnel, operating room personnel are subjected to high levels of mental workload, because they are always taking important decisions that are related to patient life and safety (19, 20).
To our knowledge, there was not any published study about the association between mental workload and fatigue in operating room personnel of hospitals. Therefore, we decided to study fatigue and mental workload prevalence in the operating room personnel and the association between mental workload and fatigue. We hope to provide a scientific basis for management measures in order to reduce the mental workload and consequently the fatigue in the personnel and eventually increase the patient safety in the operating room.
 
Materials and Methods
In a descriptive study, mental workload and its association with fatigue in operating room personnel of Besat, Fatemieh, Tamin ejtemaei, Farshchian and Shahid Beheshti hospitals, Hamadan, Iran, were investigated in 2016.
Based on census method, 188 cases of operating room personnel including surgeons, nurses, operating room and anesthesia technicians who would like to participate in the research voluntarily were recruited. All of the participants were assured that their information will remain confidential to the researcher. Moreover, participants were not asked to enter their names in the demographic questionnaire. Demographic characteristics of the participants include age, gender, job, marriage status, work experience, educational degree, monthly work-hours, type of shift work (fixed night shift, fixed morning shift, fixed evening shift, and rotating shift work), working in multiple hospitals, expertise and type of employment were collected using a demographic characteristics questionnaire.
CIS20R questionnaire was used to assess fatigue (21). Reliability and validity of CIS20R questionnaire were evaluated by Habib and colleagues for emergency service personnel. They obtained reliability of 0.86 for this questionnaire (22). CIS20R contains 20 questions related to 4 dimensions of fatigue including subjective fatigue, concentration, motivation and physical activity levels. Each of these dimensions has a response boxes ranging from 1 to 6 and the sum of this 4 domain score indicates overall fatigue severity. In this questionnaire, the more overall fatigue score was interpreted as the more overall fatigue severity (23).
Mental workload was assessed using NASA-TLX (24). The validity of the Persian version of this scale has been confirmed by Mohammadi et al. (α = 0.847) (9). The NASA-TLX uses six dimensions to assess workload including mental demand, physical demand, temporal demand, performance, effort, and frustration. This multidimensional index estimates workload during work or immediately after work (25-27).
After giving a brief description to the main objectives of the study, questionnaires were completed by participants.
Statistical analysis was performed using SPSS software (version 16.0, SPSS Inc., Chicago, IL, USA). To find the correlation between parameters, statistical tests of Pearson correlation, analysis of variance (ANOVA) and paired t-test were used. The significance level was set at 0.05.
 
Table 1: Ratings for overall mental workload and its subscales (domains) in operating room personnel
NASA-TLX Subscales Mean SD MIN MAX
Mental demand 76.4 19.5 20 100
Physical demand 77.1 19.0 10 100
Temporal demand 76.0 17.1 27 100
Effort 76.8 15.8 23 100
Performance 75.9 17.1 20 100
Frustration 63.8 22.3 10 100
Overall workload 74.3 10.8 41.2 100
NASA-TLX: National Aeronautics and Space Administration-Task Load Index; SD: Standard deviation;
 
Results
Participants were surgeons (15.6%), nurses (22.1%), operating room technicians (22.1%) and anesthesia technicians (40.2%). In this study, 102 were women and 86 were men. Among the participants, 67 were single and 121 were married. The mean age of subjects (± standard deviation) was 32.6 ± 7.5 years, minimum and maximum age of participants was 20 and 53 years, respectively. The mean work experience of subjects was 8.78 ± 6.61 years; the minimum and maximum were 1 and 32 years respectively. The mean monthly work hours of participants were 218 ± 81.7 hours, minimum and maximum monthly work hours of participants was 70 and 400, respectively. Participants’ educational degrees were bachelor of science (BSc, 52.7%), master of science (MSc, 11.2%), specialist (11.2%), professor (6.9%), general practitioner (1.6%), associate degree (15.4%) and diploma (1%). The mean of the overall mental workload rating of participants was 74.3 ± 10.8. The average rating for the subscales of mental workload stated by participants is shown in table 1.
The mean rating for fatigue and its subscales stated by participants is listed in table 2.
 
 
 
Table 2: Mean rating for fatigue and its subscales in operating room personnel
Fatigue domains Rating range Mean SD Min Max
Subjective fatigue 8-48 26.10 7.02 9 48
Concentration 5-30 15.30 3.78 5 25
Motivation 4-24 9.43 2.63 4 18
Physical activity levels 3-18 7.53 2.51 3 16
Overall fatigue 20-120 58.40 11.90 28 97
SD: Standard deviation
 
Relationships between studied demographic variables and mental workload and overall fatigue were analyzed with Pearson correlation, analysis of variance (ANOVA) and paired t-test (Tables 3 and 4).
 
Table 3: Correlation of demographic variables with the mental workload and overall fatigue
Demographic Characteristic Mental workload Overall fatigue
P R2 P R2
Age 0.254 0.007 0.731 0.001
Work experience 0.080 0.016 0.525 0.002
Monthly work-hours 0.210 0.008 0.022 0.028
 
 
The work shift had a significant effect on overall fatigue. Since only one person was in the night shift work, there was not the feasibility of LST-test. So, pairwise comparisons were not conducted. The educational degree was significantly related to mental workload. Pairwise comparisons showed that mental workload in associate degree group was more than BSc and professor groups (P = 0.032 and P = 0.019, respectively), in BSc group was lower than MSc and specialist groups (P = 0.039 and P = 0.020, respectively), and in MSc and specialist groups was more than professor group (P = 0.019 and P = 0.012, respectively).
Pearson correlation test showed that among the different domains of mental workload, only performance and frustration had a significant correlation with overall fatigue (Table 5). Between other domains of mental workload and overall fatigue, as well as between mental workload and overall fatigue there was not any significant correlation (Table 5).
 
Table 4: Association of demographic variables with the mental workload and overall fatigue
Demographic Characteristic Mental workload Overall fatigue
P t or F P t or F
Gender 0.897 1.225 0.646 -2.111⁕
Marital status 0.931 -1.426 0.459 -1.481⁕
Working in multiple hospitals 0.833 -1.936 0.203 0.417⁕
Job 0.891 0.207 0.613 0.604
Work shift 0.458 0.785 0.018 4.131
Educational degree 0.021 2.551 0.417 1.015
Type of employment 0.117 1.991 0.912 0.176
t-value in t-test
F- value in analysis of variance (ANOVA)
Table 5:  Statistical test results for correlation between mental workload and fatigue in the operating room personnel
Mental workload domains   Fatigue domains
Subjective fatigue Concentration Motivation Physical activity levels Overall fatigue
Mental demand r 0.087 -0.020 -0.093 -0.163 -0.010
P 0.233 0.783 0.206 0.025 0.893
Physical demand r 0.223 -0.097 -0.021 -0.256 0.042
P 0.002 0.183 0.775 < 0.001 0.569
Temporal demand r 0.241 -0.015 -0.044 0.048 0.118
P 0.001 0.833 0.550 0.509 0.107
Effort r 0.094 -0.028 -0.122 -0.180 -0.019
P 0.201 0.701 0.096 0.013 0.799
Performance r -0.183 -0.342 -0.330 -0.311 -0.357
P 0.012 < 0.001 < 0.001 < 0.001 < 0.001
Frustration r 0.205 0.046 0.117 0.183 0.202
P 0.005 0.531 0.108 0.012 0.006
Overall workload r 0.200 -0.119 -0.121 -0.199 0.011
P 0.006 0.103 0.098 0.006 0.880
 

Discussion
This study showed that the mean rating of mental workload in operating room personnel was 74.3 (SD = 10.8). The maximum and minimum ratings were belonged to physical demand (mean = 77.1 ± 19.0) and frustration (63.8 ± 22.3), respectively.
In a study conducted to evaluate the mental workload and its affecting factors among the nurses of Kashan, Iran (Sarsangi et al.), it has been reported that the maximum rating belongs to effort and minimum rating belongs to frustration. We found that the minimum rating belongs to frustration in both studies. The mean rating of 69.5 ± 15.7 for mental workload has been reported by Sarsangi et al. that is lower than the mean of workload rating in our study. This comparison shows the importance of mental workload in operating room personnel (27).
Although the overall mental workload was significantly correlated only with work experience, certain demographic characteristics were associated with some of the mental workload subscales. Demographic characteristics, such as age, were statistically correlated with mental demand (P = 0.005), work experience with performance (P = 0.045) and monthly work-hours with effort (P = 0.004). These findings mean that when age, working history or monthly work-hours increase, the mental workload experienced by personnel also increases. Although we did not find a significant association between gender and mental workload (P = 0.883), physical demand and frustration domains of mental workload were statistically correlated with gender. So, we find that women feel greater physical workload than men. As well as gender, we did not find a significant association between marital status and mental workload (P = 0.883), but mental demand and frustration domains of mental workload were statistically correlated with marital status, so the ratings for both of these domains were higher in married than singles. Although the job (surgeons, nurses, operating room and anesthesia technicians) was not significantly correlated with mental workload and its domains (P > 0.050), the mental work in surgeons was higher than other jobs.
The mean rating of overall mental workload in this study (74.3) was less than the mean rating obtained in the study of mental workload among the nurses of intensive care unit (82.3) and was higher than the mean rating obtained among the nurses of the orthopedic unit (63.5) in Malekpour study (28). The findings of Malekpour study show that mental workload is different in nurses of different units, but this difference was not found in different jobs in our study. The overall mental workload in this study was also more than that of has been reported in intensive care unit (ICU) nurses (71.4) (29). This finding shows the importance of mental workload in operating room personnel.
We did not find a significant association between shift work and mental workload (P = 0.783), which can be due to a mismatch between the number of samples in two working groups of day shift (n = 18) and night shift (n = 104) workers. Unlike this study, Sarsangi et al. has found a significant association between mental workload and age and type of work shift. Here, we can say again that this can be due to the mismatch between the number of samples in groups and Small sample size. But our study is consistent with Sarangis’ report, showing that the mental workload has a significant correlation with work experience (27).
Another study by Habibie et al. has found that overall fatigue, subjective fatigue, concentration, motivation, and physical activity levels in emergency service personnel were 44.44%, 49.40%, 45.40%, 38.75%, and 37.22%, respectively (22). Compared to Habibie’s results (22), we can say that overall fatigue and its domains are more severe in operating room personnel than emergency service personnel. Moreover, the severity of fatigue domains in our study were higher than that of has been reported in workers exposed to jute dust, wood dust, chemicals and office workers (30). These results show the importance of fatigue in operating room personnel.
In this study, gender was not significantly correlated with overall fatigue but Raftopoulos et al. reported that fatigue prevalence in female nurses (93%) is more than males (87.5%) (31). This inconsistency in results may be due to different sample sizes in two studies.
Statistical test results showed that only performance and frustration have a significant inverse correlation with overall fatigue. This means that feeling lower fatigue rate is inversely proportional to a better performance. A similar correlation was also found between performance and concentration, and motivation and physical activity levels. These results of our study are consistent with barker et al. findings that have assessed fatigue in nurses (32). Small sample size especially the low number of surgeons was one of the drawbacks of our study. We suggest that other studies with a larger sample size should address the mental workload and fatigue as well as human errors resulting from higher mental workload and fatigue. Such studies will be useful to policy-makers of healthcare system to improve the work time scheduling, work shifts and the maximum number of surgeries that personnel can take part in.
 
Conclusion
In general, the results of this study showed that the mental workload in the operating room personnel is high. These personnel also feel fatigue to some degrees. By examining the different domains of fatigue it was observed that the mental workload is significantly correlated with mental fatigue. It can be concluded that mental workload may be correlated with fatigue and reducing the mental workload in operating room personnel may reduce fatigue.
 
Acknowledgments
The study was funded by the vice-chancellor for research and technology, Hamadan University of Medical Sciences (No. 9304242115). We would like to thank this university for cooperation and financial support. We also would like to thank the participants of this study.
 
Conflict of interest: None declared.
 
References
 
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  2. Dawson D, Cleggett C, Thompson K, Thomas MJ. Fatigue proofing: the role of protective behaviours in mediating fatigue-related risk in a defence aviation environment. Accid Anal Prev 2015; 99(Pt B):465-8.
  3. Gander PH, Mulrine HM, van den Berg MJ, Smith AA, Signal TL, Wu LJ, et al. Pilot fatigue: relationships with departure and arrival times, flight duration, and direction. Aviat Space Environ Med 2014; 85(8):833-40.
  4. Omidvari M. Examining the workplace heat effects on the workers precocious fatigue and their reduction of efficacy in Behshar Oil Refinery Company [MSc thesis]. Tehran: Tarbiat Modares University; 1995.
  5. Amundsen AH, Sagberg F. Hours of service regulations and the risk of fatigue-and sleep-related road accidents. A literature review. Swedish: National Road Administration, Institute of Transport Economics; 2003 May. 34 p. Rport No.:659/2003.
  6. Owens JA. Sleep loss and fatigue in healthcare professionals. J Perinat Neonatal Nurs 2007; 21(2):92-100.
  7. de Fatima Marinho de Souza M, Messing K, Menezes PR, Cho HJ. Chronic fatigue among bank workers in Brazil. Occup Med (Lond) 2002; 52(4):187-94.
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  10. Yurko YY, Scerbo MW, Prabhu AS, Acker CE, Stefanidis D. Higher mental workload is associated with poorer laparoscopic performance as measured by the NASA-TLX tool. Simul Healthc 2010; 5(5):267-71.
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  15. Hill SG, Iavecchia HP, Byers JC, Bittner AC, Zaklade AL, Christ RE. Comparison of four subjective workload rating scales. Hum Factors 1992; 34(4):429-39.
  16. Saito K. Measurement of fatigue in industries. Ind Health 1999; 37(2):134-42.
  17. Sinha A, Singh A, Tewari A. The fatigued anesthesiologist: A threat to patient safety? J Anaesthesiol Clin Pharmacol 2013; 29(2):151-9.
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  28. Malekpour F, Mohammadian Y, Malekpour AR,
    Mohammadpour Y, Sheikh Ahmadi A, Shakarami A. Assessment of mental workload in nursing by using NASA-TLX. Journal of Urmia Nursing And Midwifery Faculty 2014; 11(11):892-899.
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* Corresponding author: Pejman Mohammadi, Dept. of Occupational Health, School of Public Health, Hamadan University of Medical Sciences, Hamadan, Iran.
E-mail: Pmohammadi64@gmail.com
Type of Study: original article | Subject: Occupational Health
Received: 2017/05/13 | Accepted: 2017/07/31 | ePublished: 2017/10/25

References
1. Hartzler BM. Fatigue on the flight deck: the consequences of sleep loss and the benefits of napping. Accid Anal Prev 2014; 62:309-18. [DOI] [PubMed]
2. Dawson D, Cleggett C, Thompson K, Thomas MJ. Fatigue proofing: the role of protective behaviours in mediating fatigue-related risk in a defence aviation environment. Accid Anal Prev 2015; 99(Pt B):465-8. [PubMed]
3. Gander PH, Mulrine HM, van den Berg MJ, Smith AA, Signal TL, Wu LJ, et al. Pilot fatigue: relationships with departure and arrival times, flight duration, and direction. Aviat Space Environ Med 2014; 85(8):833-40. [DOI] [PubMed]
4. Omidvari M. Examining the workplace heat effects on the workers precocious fatigue and their reduction of efficacy in Behshar Oil Refinery Company [MSc thesis]. Tehran: Tarbiat Modares University; 1995.
5. Amundsen AH, Sagberg F. Hours of service regulations and the risk of fatigue-and sleep-related road accidents. A literature review. Swedish: National Road Administration, Institute of Transport Economics; 2003 May. 34 p. Rport No.:659/2003. [Report]
6. Owens JA. Sleep loss and fatigue in healthcare professionals. J Perinat Neonatal Nurs 2007; 21(2):92-100. [DOI] [PubMed]
7. de Fatima Marinho de Souza M, Messing K, Menezes PR, Cho HJ. Chronic fatigue among bank workers in Brazil. Occup Med (Lond) 2002; 52(4):187-94. [DOI] [PubMed]
8. Sasaki T, Iwasaki K, Mori I, Hisanaga N, Shibata E. Overtime, job stressors, sleep/rest, and fatigue of Japanese workers in a company. Ind Health 2007; 45(2):237-46. [DOI] [PubMed]
9. Mohammadi M, Mazloumi A, Nasl Saraji J, Zeraati H. Designing questionnaire of assessing mental workload and determine its validity and reliability among ICUs nurses in one of the TUMS's hospitals. Journal of School of Public Health and Institute of Public Health Research. 2013; 11(2):87-96. [Article]
10. Yurko YY, Scerbo MW, Prabhu AS, Acker CE, Stefanidis D. Higher mental workload is associated with poorer laparoscopic performance as measured by the NASA-TLX tool. Simul Healthc 2010; 5(5):267-71. [DOI] [PubMed]
11. Johanssen G, Moray N, Pew R, Rasmussen J, Sanders A, Wickens C. Final report of experimental psychology group. In: Moray N, editor. Mental workload. 1st ed. New York City, United States: Springer Publishing; 1979. P. 101-14. [Book] [DOI]
12. Tattersall AJ, Foord PS. An experimental evaluation of instantaneous self-assessment as a measure of workload. Ergonomics 1996; 39(5):740-8. [DOI] [PubMed]
13. Yeh YY, Wickens ChD. Dissociation of performance and subjective measures of workload. Hum Factors 1988; 30(1):111-20. [Article] [DOI]
14. Byers JC, Bittner AC, Hill SG. Traditional and raw task load index (TLX) correlations: Are paired comparisons necessary? In: Mital A, editor. Advances in industrial ergonomics and safety I. 1st ed. Abingdon-on-Thames, United Kingdom: Routledge, Taylor & Francis; 1989:481-5. [Article]
15. Hill SG, Iavecchia HP, Byers JC, Bittner AC, Zaklade AL, Christ RE. Comparison of four subjective workload rating scales. Hum Factors 1992; 34(4):429-39. [Article] [DOI]
16. Saito K. Measurement of fatigue in industries. Ind Health 1999; 37(2):134-42. [DOI] [PubMed]
17. Sinha A, Singh A, Tewari A. The fatigued anesthesiologist: A threat to patient safety? J Anaesthesiol Clin Pharmacol 2013; 29(2):151-9. [DOI] [PubMed]
18. Kurmann A, Tschan F, Semmer NK, Seelandt J, Candinas D, Beldi G. Human factors in the operating room – the surgeon's view. Trends in Anaesthesia and Critical Care 2012; 2(5):224-7. [Article] [DOI]
19. Gurses AP, Carayon P. Performance obstacles of intensive care nurses. Nurs Res 2007; 56(3):185-94. [DOI] [PubMed]
20. Saremi M, Fallah MR. Subjective fatigue and medical errors among nurses in an educational hospital. Iran Occupational Health 2013; 10(4):1-8. [Article]
21. Vercoulen JH, Swanink CM, Fennis JF, Galama JM, van der Meer JW, Bleijenberg G. Dimensional assessment of chronic fatigue syndrome. J Psychosom Res 1994; 38(5):383-92. [DOI] [PubMed]
22. Habibi E, Parvari R, Khodarahmi B, Dehghan HA, Hosseini M, Esmaili H. Assessment of the relationship between work schedule and fatigue among the emergency personnel of Isfahan, Iran using the check list individual strength standard method. Journal of Health System Research 2011; 7(6):1288-97.
23. Makowiec-Dabrowska T, Koszada-Włodarczyk W. The CIS20R questionnaire and its suitability for prolonged fatigue studies. Med Pr 2005; 57(4):335-45. [PubMed]
24. Hart SG, Staveland LE. Development of NASA-TLX (Task Load Index): results of empirical and theoretical research. Advances in Psychology 1988; 52:139-83. [Article] [DOI]
25. Gawron VJ. Human performance measures handbook. Mahwah, New Jersey London, United States: Lea Lawrence Erlbaum Associates; 2000. P.110-1. [Book]
26. Hart SG. NASA-task load index (NASA-TLX); 20 years later. Proceedings of the Human Factors and Ergonomics Society 50th Annual Meeting; 2006 ; Santa Monica: Human Factors and Ergonomics Society; 2006. P.904-8. [Article] [DOI]
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