pii: sp-00577-13
http://dx.doi.org/10.5665/sleep.4252
SLEEP QUALITY, PTSD, AND ERRORS IN TRAIN DRIVERS: POPULATION-BASED STUDY
Sleep Quality, Posttraumatic Stress, Depression, and Human Errors in Train Drivers: A Population-Based Nationwide Study in South Korea Hong Jin Jeon, MD, PhD1,2; Ji-Hae Kim, PhD1; Bin-Na Kim, MA3; Seung Jin Park, MA3; Maurizio Fava, MD2; David Mischoulon, MD, PhD2; Hong Choi, MD, PhD1; Sungwon Roh, MD, PhD4; Dongsoo Lee, MD, PhD1 1 Department of Psychiatry, Depression Center, Samsung Medical Center, Sungkyunkwan University School of Medicine, Seoul, Korea; 2Depression Clinical and Research Program, Massachusetts General Hospital, Harvard Medical School, Boston, MA; 3Seoul National University, Seoul, Korea; 4 Department of Mental Health Research, Seoul National Hospital, Seoul, Korea
Study Objectives: Human error is defined as an unintended error that is attributable to humans rather than machines, and that is important to avoid to prevent accidents. We aimed to investigate the association between sleep quality and human errors among train drivers. Design: Cross-sectional. Setting: Population-based. Participants: A sample of 5,480 subjects who were actively working as train drivers were recruited in South Korea. The participants were 4,634 drivers who completed all questionnaires (response rate 84.6%). Interventions: None Measurements: The Pittsburgh Sleep Quality Index (PSQI), the Center for Epidemiologic Studies Depression Scale (CES-D), the Impact of Event Scale-Revised (IES-R), the State-Trait Anxiety Inventory (STAI), and the Korean Occupational Stress Scale (KOSS). Results: Of 4,634 train drivers, 349 (7.5%) showed more than one human error per 5 y. Human errors were associated with poor sleep quality, higher PSQI total scores, short sleep duration at night, and longer sleep latency. Among train drivers with poor sleep quality, those who experienced severe posttraumatic stress showed a significantly higher number of human errors than those without. Multiple logistic regression analysis showed that human errors were significantly associated with poor sleep quality and posttraumatic stress, whereas there were no significant associations with depression, trait and state anxiety, and work stress after adjusting for age, sex, education years, marital status, and career duration. Conclusions: Poor sleep quality was found to be associated with more human errors in train drivers, especially in those who experienced severe posttraumatic stress. Keywords: depression, human error, sleep quality, train drivers, trauma Citation: Jeon HJ, Kim JH, Kim BN, Park SJ, Fava M, Mischoulon D, Choi H, Roh S, Lee D. Sleep quality, posttraumatic stress, depression, and human errors in train drivers: a population-based nationwide study in South Korea. SLEEP 2014;37(12):1969-1975.
INTRODUCTION Human error is defined as “any deviation from expected human performance and not intended by the actor.” 1 Human error is, of course, inevitable and an expected part of anyone’s work. Research on human error has focused on attention as a primary cause or contributing factor in disasters and accidents in industries such as the transportation system involving trains and aircraft, the medical system, and nuclear power.2 Train accidents have caused a large number of fatalities and injuries; for example, notable train accidents occurred in Spain and New York in 2013. The Spain crash killed 80 passengers and injured 140, and the New York derailment killed four passengers and injured 67, as reported by CNN. To reduce train accidents, risk factors related to errors caused by train drivers should be investigated and prevented. Poor sleep quality is a common condition that is associated with work-related fatigue,3 impaired cognitive functions such as diminished attention and executive functions,4 and depression and anxiety disorders.5 Previous studies indicate that shift
Submitted for publication September, 2013 Submitted in final revised form May, 2014 Accepted for publication June, 2014 Address correspondence to: Dongsoo Lee, MD, PhD, Professor, Samsung Medical Center, Sungkyunkwan University School of Medicine, Number 50 Irwon-dong, Gangnam-gu, Seoul 135-710, Korea; Tel: +82 2 3410 3581; Fax: +82 2 3410 0050; E-mail: [email protected] SLEEP, Vol. 37, No. 12, 2014
work and irregular working times cause disruptions of the diurnal rhythm and poor sleep quality,6,7 which are usually unavoidable for train drivers who perform shift work. In addition, they commonly experience unpredictable accidents, such as the injury or death of passengers (including suicide attempts where people jump in front of a train), which can cause them severe posttraumatic stress. Poor sleep quality8 and impairment in cognitive functioning9 are common among individuals with posttraumatic stress disorder (PTSD). In particular, train drivers are a homogenous group who share similar work, and educational and socioeconomic backgrounds. They need to make sustained efforts to avoid human errors when driving trains. Therefore, they are good candidates for evaluating associations between human errors and associated factors, without the influence of other confounding factors. However, no previous large studies have been performed on the association between sleep quality and human errors according to the experience of posttraumatic stress in a large populationbased study. The specific aim of the current study was to examine factors associated with human errors in train drivers including sleep quality, depression, anxiety, and posttraumatic experience in a large, national, population-based study of Korean train drivers. To the best of our knowledge, this is the largest study of human errors of train drivers. The target population consisted of all of the train drivers actively working in South Korea in July 2012, a total of 5,480 drivers. We hypothesized that poor sleep quality would be associated with increased human errors in
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Sleep and Train Drivers—Jeon et al.
train drivers, and that this association would be stronger in those who had experienced posttraumatic stress. METHOD Study Population Participants were recruited from the Human Error Study for Korean Train Drivers, a nationwide survey for prevention of human errors among train drivers. The Institutional Review Board of Samsung Medical Center approved this study. This study was based on all of the 5,480 Korean train drivers who were currently driving trains during the study period. A pilot study was conducted on 40 train drivers with face-to-face interviews by two psychologists in May to June in 2012 before beginning the main survey to evaluate the validity of the questionnaire. Data were collected from July to August of 2012, using the web-based survey system of Samsung Medical Center. All subjects were fully informed about the aims and methods of the study prior to completing the interview and informed consent was obtained prior to participation. In order to ensure confidentiality of the participants, the study researchers constructed a new website using the external server system of Samsung Medical Center, with higher security and data encryption, and neither personal identification nor data were served to the Korean National Railroad Corporation (KORAIL). The identification to log into the website was fully anonymous, with letters with randomization used, and passwords made by the subjects themselves after logging in. Participants could reply to the questionnaire on their personal computer at any time that was convenient for them, at home or work. During the web-based interview, participants were given feedback about response errors or omissions and they were required to respond again. Measure of Sleep The Pittsburgh Sleep Quality Index (PSQI)10 was applied to evaluate sleep quality. The PSQI is a self-rated questionnaire that is widely used to assess sleep quality and disturbance during the previous month. Nineteen individual items generate seven component scores (range 0–3, with higher scores indicating worse sleep) on subjective sleep quality, sleep latency, sleep duration, habitual sleep efficiency, sleep disturbances, use of sleeping medication, and daytime dysfunction. The sum of the scores for the seven components yields one sleep quality score (range 0-21). A global PSQI score greater than 5 yielded a diagnostic sensitivity of 89.6% and specificity of 86.5% (kappa = 0.75, P < 0.001) in distinguishing good and poor sleepers.10 It has been translated into the Korean version and validated, which showed that Cronbach α coefficient for internal consistency of the total score of the PSQI was 0.84, and the test-retest correlation coefficient was 0.65 for the total score (P < 0.001).11
passing failure is an accident in which a train has run through a stop sign and skips a station at which it should stop. Mishandling failure is an accident in which a train is out of order because of mishandling of the train. Subjects were divided into two groups according to less than one error or one or more per 5 y of service career, which was defined as 5% of all train drivers from the statistical distribution of errors. Two questions were applied to assess the human errors of train drivers, “Have you experienced an accident?” and “How many times have you experienced things such as derailment, station passing failure, and mishandling failure while driving a train, except for railway death and injury?” Their career as train drivers was assessed by a question, “How long has your career as a train driver been?” The mean rate of human errors per year was calculated from the number of human errors divided by the length of the train driver’s career. Other Measures Demographic characteristics (age, education years, sex, and marital status) and duration of career as train drivers were obtained from the survey. The Center for Epidemiologic Studies Depression Scale (CES-D)12 was applied to evaluate the severity of depression. It is a 20-item questionnaire with a fivepoint scale used for assessing depressive symptomatology in the general population, and its Korean version also showed high reliability (Cronbach α = 0.893) and test-retest reliability (Pearson r coefficient, 0.68; P < 0.001) with cutoff at 21 points.13 The Impact of Event Scale-Revised (IES-R)14 was applied to measure posttraumatic stress over the lifetime. It is a 22-item self-rating scale of trauma-related symptoms including hyperarousal symptoms. Its Korean version also showed high reliability and validity for the assessment of PTSD symptom severity, and its cutoff score to indicate the experience of serious trauma was more than 25 points.15 The State-Trait Anxiety Inventory (STAI)16, which is a 20-item self-report instrument developed to assess levels of situation-related state anxiety (STAI-S) and trait anxiety (STAI-T), was applied to measure the severity of anxiety. The Korean version of STAI was validated.17 The Korean Occupational Stress Scale (KOSS)18 was applied to measure work stress. The KOSS was developed to evaluate unique and specific occupational stress in Korean employees.19 The questions for “exposure during train driving” consisted of “trouble with passengers,” “injury to passengers,” “death except for suicide,” and “completed suicide.”
Measure of Human Error Human errors of train drivers included derailment, station passing failure, and mishandling failure and did not include accidents involving railway deaths and injuries. This study was focused on human errors of train drivers, rather than on outcomes of the accidents themselves. Derailment is an accident in which a train comes off the track on which it is running. Station SLEEP, Vol. 37, No. 12, 2014
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Statistical Analysis Subjects were divided into two groups according to less than one error or one or more per 5 y of service career. The two groups were compared regarding age, sex, education years, marital status, number of human errors, career duration, depression, posttraumatic stress, trait and state anxiety, work stress, exposure during train driving, and total scores and sleep variables of the PSQI with Student t-test or chi-square test (two-tailed). Sleep efficiency (%) was calculated from the number of hours spent in bed divided by the number of hours slept. Two multiple logistic regression analyses were performed to evaluate associations with human errors as a dependent variable, after adjusting for age, sex, education years, marital status, and career duration. First, independent variables were sleep quality, sleep onset Sleep and Train Drivers—Jeon et al.
Table 1—Demographic and clinical profiles of train drivers according to experience of human errors. Human Errors of Train Drivers Profiles Age Education, years Number of human errors Career duration of train driving, years Trait anxiety a State anxiety b Work stress c Male sex Marital status Married Unmarried Divorced/separated/widowed Exposed during train driving Trouble with passengers Injury to passengers Death except for suicide Completed suicide Depression d Severe posttraumatic stress e
Statistics
Total (n = 4,634) Mean (SD) 45.3 (9.4) 13.0 (3.7) 0.9 (2.2) 17.4 (8.6) 34.8 (9.1) 35.4 (9.4) 46.7 (11.2)
≥ 1 error/5 y (n = 349) Mean (SD) 41.9 (7.2) 13.9 (3.3) 5.5 (5.4) 12.5 (7.7) 34.9 (9.0) 35.7 (9.4) 46.6 (12.2)
< 1 error/5 y (n = 4,285) Mean (SD) 45.8 (9.4) 12.9 (3.7) 0.5 (0.9) 18.1 (8.3) 34.8 (9.1) 35.4 (9.4) 46.7 (11.2)
t
P
7.7 5.3 16.0 12.2 0.3 0.5 0.1
< 0.0001 < 0.0001 < 0.0001 < 0.0001 0.79 0.61 0.94
n (%) 4,597 (99.2)
n (%) 342 (98.0)
n (%) 4,255 (99.3)
χ2 7.0
P 0.008
4,314 (93.1) 260 (5.6) 60 (1.3)
307 (88.0) 38 (10.9) 4 (1.1)
4,007 (93.5) 222 (5.2) 56 (1.3)
19.9
< 0.0001
371 (8.0) 795 (17.2) 1,076 (23.2) 1,471 (31.7) 202 (4.4) 599 (12.9)
68 (19.5) 88 (25.2) 95 (27.2) 103 (29.5) 30 (8.6) 86 (24.6)
303 (7.1) 707 (16.5) 981 (22.9) 1,368 (31.9) 172 (4.0) 513. (12.0)
67.5 17.3 3.4 0.9 16.3 46.0
< 0.0001 < 0.0001 0.07 0.35 < 0.0001 < 0.0001
State-Trait Anxiety Inventory-Trait (STAI-T). b State-Trait Anxiety Inventory-State (STAI-S). c Korean Occupational Stress Scale (KOSS). d Center for Epidemiologic Studies Depression Scale (CES-D) ≥ 21. e Impact of Event Scale-Revised (IES-R) ≥ 25. SD, standard deviation.
a
latency, sleep at night, sleep efficiency, and poor sleep quality; secondary variables were trait and state anxiety, work stress, depression, poor sleep quality, and severe posttraumatic stress. Statistical analysis was performed by using SPSS 17.0 (SPSS, Inc., Chicago), and the level of significance was set at P < 0.05. RESULTS Demographic and Clinical Profiles Of the 4,718 train drivers who participated in the survey, 84 were excluded because of an incomplete response. As a result, a total of 4,634 train drivers completed the interview (response rate 84.6%). The mean age of the subjects who completed the survey was 45.3 ± 9.4 y, with 13.0 ± 3.7 y of education, 99.2% male, and 93.1% married. Their mean service career as train drivers was 17.4 ± 8.6 y. Of the 4,634 train drivers who completed the questionnaires, the number of human errors was 0.06 times/y (standard deviation [SD] 0.02, minimum 0 and maximum 5). A total of 349 (7.5%) were classified into those who experienced one or more errors for every 5 y of service. Demographic and clinical profiles of the two groups are shown in Table 1. Train drivers with human errors (≥ 1 error/5 y) were younger, male, had more education years, short career duration, tended to be unmarried compared to those without human errors (< 1 error/5 y). Train drivers with human errors showed higher rates of depression and severe posttraumatic stress, and more exposure to trouble with passengers and injury of passengers than those without, SLEEP, Vol. 37, No. 12, 2014
whereas there were no significant differences in trait and state anxiety and work stress, and exposure to death except for suicide and completed suicide between the two groups. Sleep Quality, PSQI The mean score for the PSQI was 3.5 (SD 2.45, range 0 to 19), with 17.0% scoring above the cutoff value (> 5). The PSQI was compared between train drivers with and without ≥ 1 error/5 y of human errors (Table 2). Train drivers with human errors showed significantly higher scores on the PSQI total score (t = 6.2, P < 0.0001), sleep onset latency (t = 3.5, P < 0.0001), sleep duration at night (t = 3.1, P = 0.002), and poor sleep quality (χ2 = 37.0, P < 0.0001) than those without. No significant differences were found in sleep efficiency between the two groups (t = 0.6, P = 0.58).
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Posttraumatic Stress in Train Drivers With Poor Sleep Quality As shown in Figure 1, train drivers who had experienced poor sleep quality showed higher number of human errors than those who had not (degrees of freedom [df] = 904.7, t = 4.7, P < 0.001). Among those who had poor sleep quality, those who experienced severe traumatic stress showed significantly higher number of human errors than those who did not (df = 475.1, t = 2.3, P = 0.02). Multiple Logistic Regression Analyses for Human Errors The results of the multiple logistic regression analyses are shown in Table 3. Train drivers who committed human errors Sleep and Train Drivers—Jeon et al.
Table 2—Sleep quality and self-reported sleep variables according to experience of human errors. Human Errors of Train Drivers Profiles Sleep quality (PSQI total score) Sleep variables, by PSQI Sleep onset latency, min Sleep duration at night, h Sleep efficiency, % PSQI > 5 (poor sleep quality)
Statistics
Total (n = 4,634) Mean (SD) 3.5 (2.5)
≥ 1 error/5 y (n = 349) Mean (SD) 4.4 (3.0)
< 1 error/5 y (n = 4,285) Mean (SD) 3.4 (2.4)
t
P
6.2
< 0.0001
20.7 (17.0) 6.8 (1.2) 86.8 (13.6)
24.1 (18.8) 6.6 (1.2) 87.2 (13.8)
20.5 (16.9) 6.8 (1.2) 86.8 (13.6)
3.5 3.1 0.6
< 0.0001 0.002 0.58
n (%) 792 (17.0)
n (%) 100 (29.0)
n (%) 685 (16.2)
χ2 37.0
P < 0.0001
PSQI, Pittsburgh Sleep Quality Index, SD, standard deviation.
Table 3—Multiple logistic regression analysis of human errors for sleep quality and trauma experience. More Than One Human Error Per 5 y Profiles Trait anxiety a State anxiety b Work stress c Depression d Poor sleep quality e Severe posttraumatic stress f
AOR (95% CI) 1.0 (1.0-1.0) 1.0 (1.0-1.0) 1.0 (1.0-1.0) 1.3 (0.8-2.0) 1.7 (1.3-2.2) 2.2 (1.6-2.9)
P 1.0 0.5 0.4 0.3 < 0.001 < 0.001
Analysis adjusted for age, sex, education years, marital status, and career duration. a Measured by the State-Trait Anxiety Inventory-Trait (STAI-T). b State-Trait Anxiety Inventory-State (STAI-S). c Korean Occupational Stress Scale (KOSS). d Center for Epidemiologic Studies Depression Scale (CES-D) ≥ 21. e Pittsburgh Sleep Quality Index (PSQI) > 5. f Impact of Event Scale-Revised (IES-R) ≥ 25. AOR, adjusted odds ration; CI, confidence interval.
Figure 1—Poor sleep quality and human errors with and without experience of severe posttraumatic stress in train drivers of South Korea (n = 4,634). Exposure to severe posttraumatic stress was defined as 25 or higher scores of the Impact of Event Scale-Revised (IES-R). CI, confidence interval.
were significantly associated with poor sleep quality (AOR [adjusted odds ratio] = 1.7, 95% confidence interval [CI] 1.3-2.2) and posttraumatic stress (AOR = 2.2, 95% CI 1.6-2.9), whereas there were no significant associations with depression, trait and state anxiety, and work stress after adjusting for age, sex, education years, marital status, and career duration. DISCUSSION This is the first study from a large population-based survey to investigate an association between sleep quality and human errors according to the experience of posttraumatic stress. The main finding of this study is that poor sleep quality was associated with more human errors in train drivers, especially in those who experienced serious posttraumatic stress. Human SLEEP, Vol. 37, No. 12, 2014
errors were associated with both sleep quality and posttraumatic stress after adjusting for age, sex, education years, marital status, trait anxiety, state anxiety, work stress, and depression. This study showed that poor sleep quality is a common condition among train drivers. A total of 17.0% of train drivers suffer from poor sleep quality, which was assessed as being present when scores were greater than 5 points on the PSQI total score. Although there are no previous studies of prevalence of poor sleep in train drivers, this figure is less frequent than 26.4% of the general Japanese male adult population20 and 26.5% of the Austrian male population,21 and 30.03% of the population in the German Health Survey.22 This study also showed that the rate of poor sleep quality was 1.7 times higher among train drivers who experienced more human errors than those who had not. In addition, we found that train drivers with human errors showed poor sleep quality, higher PSQI total scores, short sleep at night, and longer sleep latency than those without errors, but no significant differences were found in sleep efficiency. Shahly et al.23 estimated that insomnia was associated with 7.2% of all costly workplace accidents and errors and one-fourth of all the costs of these incidents.
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Sleep and Train Drivers—Jeon et al.
An important finding of this study is that poor sleep quality is more strongly associated with human errors in those who experienced serious posttraumatic stress than in those who did not. Train drivers handle a large vehicle with many passengers and continue their work throughout their life, so they commonly experience traumatic accidents such as trouble with passengers, or injury and death of passengers including suicides by patients jumping in front of a running train. Notably, this study indicated that train drivers commonly experience these issues, and suffer from posttraumatic stress, which was related to human errors along with sleep quality. In previous studies, prevalence rates of PTSD were 16–17% among train drivers experiencing “person under the train” incidents.24 PTSD can be diagnosed if a person is exposed to one or more life-threatening events, and a group of symptoms such as re-experiencing the events in nightmares and having disturbing recurring flashbacks, having an avoidance pattern of behavior or having numbing of the memories of the event; and experiencing hyperarousal symptoms that continue for more than 1 mo after the traumatic event.25 Previous studies revealed that the symptoms of PTSD have a bidirectional influence on poor sleep quality.8,26 PTSD involves deficits in information processing that may reflect hypervigilance and deficient inhibitory control,27 and co-occurrence with major depressive disorder increases the risk for suicidal behavior.28 PTSD is commonly associated with alcohol dependence, which is associated with high levels of severity.29 Among the types of posttraumatic stress, train drivers who experienced trouble with passengers or injury of passengers committed more errors than those who experienced death except for attempted suicide and completed suicide. This finding suggests that stress associated with human errors may be related to errors that are within the drivers’ personal responsibility. Accidental death and suicide are serious traumatic experiences to the general population, but the drivers themselves are usually not responsible for these events. These results suggest that the subjective perception of the severity of the trauma may be important in producing posttraumatic stress, poor sleep quality, and human errors in train drivers. Train drivers with posttraumatic stress worried about being involved in accidents and showed the most symptoms of distress, and sometimes they suffered from long-term psychological distress.30 Although depression was also associated with human errors, no significance was found after controlling for poor sleep quality. This finding indicates that human errors are more strongly related to poor sleep quality than depression, although poor sleep quality is one of the diagnostic criteria of major depression.25 Both trait and state anxiety showed no significant association with human errors. As a previous study reported that optimal anxiety can boost early error detection mechanisms,31 this study revealed that anxiety was not significantly associated with human errors. This study revealed that work stress also showed no association with human errors, although a previous study reported that work stress is strongly linked to disturbed sleep and impaired awakening in the general population.32 The human errors in this study were measured throughout the career duration of train drivers as a state variable, whereas sleep, depression, anxiety, and work stress were measured within 1 mo or 1 w as trait variables. It suggested that current sleep quality of train drivers is associated with state of human errors of train drivers. SLEEP, Vol. 37, No. 12, 2014
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The train drivers with more human errors had less train driving experience than those with fewer errors. Less experience is associated with greater crash risk in other transportation modes such as motor vehicle driving. Although posttraumatic stress can create poor sleep quality - and therefore significantly more train errors - it may be that a relative lack of experience that explains the increased rate of errors in these train drivers. Still, the train drivers with more errors did have more than 10 y of experience, so we think that lack of experience is unlikely to account for the increased error rate. Nonetheless, this cannot be completely addressed with the current data and further study is needed to evaluate this issue. Despite its strengths, such as the large sample size of a homogenous group, there are several limitations to this study that should be considered when interpreting the findings. First, this is a cross-sectional survey in which information about sleep, posttraumatic stress, and depression was based on retrospective reports. Therefore, recall bias may have affected the accuracy of the responses to the questionnaires.33 Second, false negatives in the results of the questionnaires may have underestimated the real rates of human errors and posttraumatic stress. Thus, it is possible that these data underestimate the number of human errors, as information about the number of human errors was obtained through self-reporting rather than from the database of the train company. To reduce underreporting of errors and symptoms, we made every effort to ensure confidentiality of the participants, such as using an external server system with higher security and data encryption, and no provision of subjects’ personal identification and data was made to their train company, which was explained to them before starting the interview. Third, nonresponsiveness to the interview also may have impacted these results, as it has been reported that nonrespondents have higher rates of mental disorders than respondents.34,35 Fourth, further study is needed to consider medical illness and medications for depression, anxiety, insomnia, and somnolence in train drivers. We plan to establish a mental health promotion system for train drivers. In conclusion, we found that poor sleep quality and posttraumatic stress are associated with human errors of train drivers. Poor sleep quality is more strongly associated with increased human errors in train drivers, especially those who experienced severe posttraumatic stress than those who did not. These findings suggest that it is important to reduce human errors and ultimately prevent railway disasters for train drivers by improving sleep quality, especially for train drivers who have experienced posttraumatic stress. ACKNOWLEDGMENTS The authors thank the Samsung Statistical Support Team, chief Dr. Seon-Woo Kim, for statistical support. DISCLOSURE STATEMENT This study was supported by the Korean National Railroad Corporation (KORAIL). This study was also supported by the Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Education, Science and Technology (No. 2011-0013064), and the Samsung Medical Center Clinical Research Development Program (CRDP) Grant SMO1131461. Dr. Fava has received Sleep and Train Drivers—Jeon et al.
research support from Abbott Laboratories, Alkermes, Aspect Medical Systems, Astra-Zeneca, BioResearch, BrainCells, Inc., Bristol-Myers Squibb Company, Cephalon, Clinical Trial Solutions, LLC, Eli Lilly & Company, EnVivo Pharmaceuticals, Inc., Forest Pharmaceuticals Inc., Ganeden, GlaxoSmithKline, J & J Pharmaceuticals, Lichtwer Pharma GmbH, Lorex Pharmaceuticals, NARSAD, NCCAM, NIDA, NIMH, Novartis, Organon Inc., PamLab, LLC, Pfizer Inc., Pharmavite, Roche, SanofiAventis, Shire, Solvay Pharmaceuticals, Inc., Synthelabo, and Wyeth-Ayerst Laboratories. He has served as an advisor and consultant to Abbott Laboratories, Affectis Pharmaceuticals AG, Amarin, Aspect Medical Systems, Astra-Zeneca, Auspex Pharmaceuticals, Bayer AG, Best Practice Project Management, Inc., BioMarin Pharmaceuticals, Inc., Biovail Pharmaceuticals, Inc., BrainCells, Inc., Bristol-Myers Squibb Company, Cephalon, Clinical Trials Solutions, LLC, CNS Response, Compellis, Cypress Pharmaceuticals, Dov Pharmaceuticals, Eisai, Inc., Eli Lilly & Company, EPIX Pharmaceuticals, Euthymics Bioscience, Inc., Fabre-Kramer, Pharmaceuticals, Inc., Forest Pharmaceuticals Inc., GlaxoSmithKline, Grunenthal GmBH, Janssen Pharmaceutica, Jazz Pharmaceuticals, J & J Pharmaceuticals, Knoll Pharmaceutical Company, Labopharm, Lorex Pharmaceuticals, Lundbeck, MedAvante Inc., Merck, Methylation Sciences, Neuronetics, Novartis, Nutrition 21, Organon Inc., PamLab, LLC, Pfizer Inc., PharmaStar, Pharmavite, Precision Human Biolaboratory, Prexa Pharmaceuticals, Inc., PsychoGenics, Psylin Neurosciences, Inc., Ridge Diagnostics, Inc., Roche, Sanofi-Aventis, Sepracor, Schering-Plough, Solvay Pharmaceuticals, Inc., Somaxon, Somerset Pharmaceuticals, Synthelabo, Takeda, Tetragenex, TransForm Pharmaceuticals, Inc., Transcept Pharmaceuticals, Vanda Pharmaceuticals Inc., Wyeth-Ayerst Laboratories. He has received speaking and publishing honoraria from Adamed, Co., Advanced Meeting Partners, American Psychiatric Association, American Society of Clinical Psychopharmacology, Astra-Zeneca, Belvoir, Boehringer-Ingelheim, Bristol-Myers Squibb Company, Cephalon, Eli Lilly & Company, Forest Pharmaceuticals Inc., GlaxoSmithKline, Imedex, Novartis, Organon Inc., Pfizer Inc., PharmaStar, MGH Psychiatry Academy/Primedia, MGH Psychiatry Academy/Reed-Elsevier, UBC, and Wyeth-Ayerst Laboratories. He holds equity in Compellis. He currently holds a patent for SPCD and a patent application for a combination of azapirones and bupropion in MDD, and has received copyright royalties for the MGH CPFQ, SFI, ATRQ, DESS, and SAFER diagnostic instruments. Dr Mischoulon has received research support from the Bowman Family Foundation, FisherWallace, Ganeden, Nordic Naturals, and Methylation Sciences, Inc. (MSI). He has received honoraria for consulting, speaking, and writing from the Massachusetts General Hospital Psychiatry Academy. He has received royalties from Lippincott Williams & Wilkins for published book “Natural Medications for Psychiatric Disorders: Considering the Alternatives.” The other authors have indicated no financial conflicts of interest. The work was performed at Samsung Medical Center, Sungkyunkwan University School of Medicine, Seoul, Korea. REFERENCES
1. Senders JW, Moray NP. Human Error: Cause, Prediction, and Reduction. Hillsdale, NJ: Lawrence Erlbaum Associates, 1991.
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2. Spencer FC. Human error in hospitals and industrial accidents: current concepts. J Am Coll Surg 2000;191:410–8. 3. Querstret D, Cropley M. Exploring the relationship between work-related rumination, sleep quality, and work-related fatigue. J Occup Health Psychol 2012;17:341–53. 4. Benitez A, Gunstad J. Poor sleep quality diminishes cognitive functioning independent of depression and anxiety in healthy young adults. Clin Neuropsychol 2012;26:214–23. 5. Neckelmann D, Mykletun A, Dahl AA. Chronic insomnia as a risk factor for developing anxiety and depression. Sleep 2007;30:873–80. 6. Bostock S, Steptoe A. Influences of early shift work on the diurnal cortisol rhythm, mood and sleep: within-subject variation in male airline pilots. Psychoneuroendocrinology 2013;38:533–41. 7. Harma M, Tenkanen L, Sjoblom T, Alikoski T, Heinsalmi P. Combined effects of shift work and life-style on the prevalence of insomnia, sleep deprivation and daytime sleepiness. Scand J Work Environ Health 1998;24:300–7. 8. Lamarche LJ, De Koninck J. Sleep disturbance in adults with posttraumatic stress disorder: a review. J Clin Psychiatry 2007;68:1257–70. 9. Barrett DH, Green ML, Morris R, Giles WH, Croft JB. Cognitive functioning and posttraumatic stress disorder. Am J Psychiatry 1996;153:1492–4. 10. Buysse DJ, Reynolds CF 3rd, Monk TH, Berman SR, Kupfer DJ. The Pittsburgh Sleep Quality Index: a new instrument for psychiatric practice and research. Psychiatry Res 1989;28:193–213. 11. Sohn SI, Kim do H, Lee MY, Cho YW. The reliability and validity of the Korean version of the Pittsburgh Sleep Quality Index. Sleep Breath 2012;16:803–12. 12. Radloff LS. The CES-D Scale: a self report depression scale for research in the general population. Appl Psychol Meas 1977;1:385–401. 13. Cho MJ, Kim KH. Use of the Center for Epidemiologic Studies Depression (CES-D) Scale in Korea. J Nerv Ment Dis 1998;186:304–10. 14. Weiss DS, Marmar CR. The impact of event scale-revised. In: Wilson J.P., Keane T.M., eds. Assessing Psychological Trauma and PTSD. New York: Guilford, 1997. 15. Eun HJ, Kwon TW, Lee SM, Kim TH, Choi MR, Cho SJ. A study on reliability and validity of the Korean version of Impact of Event ScaleRevised. J Korean Neuropsychiatr Assoc 2005;44:303–10. 16. Spielberger CD, Gorsuch RL, Lushene RE. Manual for the State-Trait Anxiety Inventory (STAI). Palo Alto, CA: Consulting Psychologists Press, 1970. 17. Kim JT. The Relationship of Trait Anxiety and Sociability. Seoul: Korea University, 1978. 18. Chang SJ, Koh SB, Kang D, et al. Developing an occupational stress scale for Korean employees. Korean J Occup Environ Med 2005;17:279–317. 19. Cho JJ, Kim JY, Chang SJ, et al. Occupational stress and depression in Korean employees. Int Arch Occup Environ Health 2008;82:47–57. 20. Doi Y, Minowa M, Uchiyama M, Okawa M. Subjective sleep quality and sleep problems in the general Japanese adult population. Psychiatry Clin Neurosci 2001;55:213–5. 21. Zeitlhofer J, Schmeiser-Rieder A, Tribl G, et al. Sleep and quality of life in the Austrian population. Acta Neurol Scand 2000;102:249–57. 22. Stein MB, Belik SL, Jacobi F, Sareen J. Impairment associated with sleep problems in the community: relationship to physical and mental health comorbidity. Psychosom Med 2008;70:913–9. 23. Shahly V, Berglund PA, Coulouvrat C, et al. The associations of insomnia with costly workplace accidents and errors: results from the America Insomnia Survey. Arch Gen Psychiatry 2012;69:1054–63. 24. Mehnert A, Nanninga I, Fauth M, Schafer I. Course and predictors of posttraumatic stress among male train drivers after the experience of ‘person under the train’ incidents. J Psychosom Res 2012;73:191–6. 25. American Psychiatric Association. Diagnostic and Statistical Manual of Mental Disorders. 4th ed. Washington, DC: American Psychiatric Press, 1994. 26. Belleville G, Guay S, Marchand A. Impact of sleep disturbances on PTSD symptoms and perceived health. J Nerv Ment Dis 2009;197:126–32. 27. Falconer E, Bryant R, Felmingham KL, et al. The neural networks of inhibitory control in posttraumatic stress disorder. J Psychiatry Neurosci 2008;33:413–22. 28. Oquendo M, Brent DA, Birmaher B, et al. Posttraumatic stress disorder comorbid with major depression: factors mediating the association with suicidal behavior. Am J Psychiatry 2005;162:560–6.
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29. Blanco C, Xu Y, Brady K, Perez-Fuentes G, Okuda M, Wang S. Comorbidity of posttraumatic stress disorder with alcohol dependence among US adults: results from National Epidemiological Survey on Alcohol and Related Conditions. Drug Alcohol Depend 2013;132:630–8. 30. Karlehagen S, Malt UF, Hoff H, et al. The effect of major railway accidents on the psychological health of train drivers--II. A longitudinal study of the one-year outcome after the accident. J Psychosom Res 1993;37:807–17. 31. Aarts K, Pourtois G. Anxiety not only increases, but also alters early errormonitoring functions. Cogn Affect Behav Neurosci 2010;10:479–92. 32. Akerstedt T, Knutsson A, Westerholm P, Theorell T, Alfredsson L, Kecklund G. Sleep disturbances, work stress and work hours: a crosssectional study. J Psychosom Res 2002;53:741–8.
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33. Patten SB. Recall bias and major depression lifetime prevalence. Soc Psychiatry Psychiatr Epidemiol 2003;38:290–-6. 34. Eaton WW, Anthony JC, Tepper S, Dryman A. Psychopathology and attrition in the epidemiologic catchment area surveys. Am J Epidemiol 1992;135:1051–9. 35. de Graaf R, Bijl RV, Smit F, Ravelli A, Vollebergh WA. Psychiatric and sociodemographic predictors of attrition in a longitudinal study: the Netherlands Mental Health Survey and Incidence Study (NEMESIS). Am J Epidemiol 2000;152:1039–47.
Sleep and Train Drivers—Jeon et al.
http://dx.doi.org/10.5665/sleep.4252
SLEEP QUALITY, PTSD, AND ERRORS IN TRAIN DRIVERS: POPULATION-BASED STUDY
Sleep Quality, Posttraumatic Stress, Depression, and Human Errors in Train Drivers: A Population-Based Nationwide Study in South Korea Hong Jin Jeon, MD, PhD1,2; Ji-Hae Kim, PhD1; Bin-Na Kim, MA3; Seung Jin Park, MA3; Maurizio Fava, MD2; David Mischoulon, MD, PhD2; Hong Choi, MD, PhD1; Sungwon Roh, MD, PhD4; Dongsoo Lee, MD, PhD1 1 Department of Psychiatry, Depression Center, Samsung Medical Center, Sungkyunkwan University School of Medicine, Seoul, Korea; 2Depression Clinical and Research Program, Massachusetts General Hospital, Harvard Medical School, Boston, MA; 3Seoul National University, Seoul, Korea; 4 Department of Mental Health Research, Seoul National Hospital, Seoul, Korea
Study Objectives: Human error is defined as an unintended error that is attributable to humans rather than machines, and that is important to avoid to prevent accidents. We aimed to investigate the association between sleep quality and human errors among train drivers. Design: Cross-sectional. Setting: Population-based. Participants: A sample of 5,480 subjects who were actively working as train drivers were recruited in South Korea. The participants were 4,634 drivers who completed all questionnaires (response rate 84.6%). Interventions: None Measurements: The Pittsburgh Sleep Quality Index (PSQI), the Center for Epidemiologic Studies Depression Scale (CES-D), the Impact of Event Scale-Revised (IES-R), the State-Trait Anxiety Inventory (STAI), and the Korean Occupational Stress Scale (KOSS). Results: Of 4,634 train drivers, 349 (7.5%) showed more than one human error per 5 y. Human errors were associated with poor sleep quality, higher PSQI total scores, short sleep duration at night, and longer sleep latency. Among train drivers with poor sleep quality, those who experienced severe posttraumatic stress showed a significantly higher number of human errors than those without. Multiple logistic regression analysis showed that human errors were significantly associated with poor sleep quality and posttraumatic stress, whereas there were no significant associations with depression, trait and state anxiety, and work stress after adjusting for age, sex, education years, marital status, and career duration. Conclusions: Poor sleep quality was found to be associated with more human errors in train drivers, especially in those who experienced severe posttraumatic stress. Keywords: depression, human error, sleep quality, train drivers, trauma Citation: Jeon HJ, Kim JH, Kim BN, Park SJ, Fava M, Mischoulon D, Choi H, Roh S, Lee D. Sleep quality, posttraumatic stress, depression, and human errors in train drivers: a population-based nationwide study in South Korea. SLEEP 2014;37(12):1969-1975.
INTRODUCTION Human error is defined as “any deviation from expected human performance and not intended by the actor.” 1 Human error is, of course, inevitable and an expected part of anyone’s work. Research on human error has focused on attention as a primary cause or contributing factor in disasters and accidents in industries such as the transportation system involving trains and aircraft, the medical system, and nuclear power.2 Train accidents have caused a large number of fatalities and injuries; for example, notable train accidents occurred in Spain and New York in 2013. The Spain crash killed 80 passengers and injured 140, and the New York derailment killed four passengers and injured 67, as reported by CNN. To reduce train accidents, risk factors related to errors caused by train drivers should be investigated and prevented. Poor sleep quality is a common condition that is associated with work-related fatigue,3 impaired cognitive functions such as diminished attention and executive functions,4 and depression and anxiety disorders.5 Previous studies indicate that shift
Submitted for publication September, 2013 Submitted in final revised form May, 2014 Accepted for publication June, 2014 Address correspondence to: Dongsoo Lee, MD, PhD, Professor, Samsung Medical Center, Sungkyunkwan University School of Medicine, Number 50 Irwon-dong, Gangnam-gu, Seoul 135-710, Korea; Tel: +82 2 3410 3581; Fax: +82 2 3410 0050; E-mail: [email protected] SLEEP, Vol. 37, No. 12, 2014
work and irregular working times cause disruptions of the diurnal rhythm and poor sleep quality,6,7 which are usually unavoidable for train drivers who perform shift work. In addition, they commonly experience unpredictable accidents, such as the injury or death of passengers (including suicide attempts where people jump in front of a train), which can cause them severe posttraumatic stress. Poor sleep quality8 and impairment in cognitive functioning9 are common among individuals with posttraumatic stress disorder (PTSD). In particular, train drivers are a homogenous group who share similar work, and educational and socioeconomic backgrounds. They need to make sustained efforts to avoid human errors when driving trains. Therefore, they are good candidates for evaluating associations between human errors and associated factors, without the influence of other confounding factors. However, no previous large studies have been performed on the association between sleep quality and human errors according to the experience of posttraumatic stress in a large populationbased study. The specific aim of the current study was to examine factors associated with human errors in train drivers including sleep quality, depression, anxiety, and posttraumatic experience in a large, national, population-based study of Korean train drivers. To the best of our knowledge, this is the largest study of human errors of train drivers. The target population consisted of all of the train drivers actively working in South Korea in July 2012, a total of 5,480 drivers. We hypothesized that poor sleep quality would be associated with increased human errors in
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train drivers, and that this association would be stronger in those who had experienced posttraumatic stress. METHOD Study Population Participants were recruited from the Human Error Study for Korean Train Drivers, a nationwide survey for prevention of human errors among train drivers. The Institutional Review Board of Samsung Medical Center approved this study. This study was based on all of the 5,480 Korean train drivers who were currently driving trains during the study period. A pilot study was conducted on 40 train drivers with face-to-face interviews by two psychologists in May to June in 2012 before beginning the main survey to evaluate the validity of the questionnaire. Data were collected from July to August of 2012, using the web-based survey system of Samsung Medical Center. All subjects were fully informed about the aims and methods of the study prior to completing the interview and informed consent was obtained prior to participation. In order to ensure confidentiality of the participants, the study researchers constructed a new website using the external server system of Samsung Medical Center, with higher security and data encryption, and neither personal identification nor data were served to the Korean National Railroad Corporation (KORAIL). The identification to log into the website was fully anonymous, with letters with randomization used, and passwords made by the subjects themselves after logging in. Participants could reply to the questionnaire on their personal computer at any time that was convenient for them, at home or work. During the web-based interview, participants were given feedback about response errors or omissions and they were required to respond again. Measure of Sleep The Pittsburgh Sleep Quality Index (PSQI)10 was applied to evaluate sleep quality. The PSQI is a self-rated questionnaire that is widely used to assess sleep quality and disturbance during the previous month. Nineteen individual items generate seven component scores (range 0–3, with higher scores indicating worse sleep) on subjective sleep quality, sleep latency, sleep duration, habitual sleep efficiency, sleep disturbances, use of sleeping medication, and daytime dysfunction. The sum of the scores for the seven components yields one sleep quality score (range 0-21). A global PSQI score greater than 5 yielded a diagnostic sensitivity of 89.6% and specificity of 86.5% (kappa = 0.75, P < 0.001) in distinguishing good and poor sleepers.10 It has been translated into the Korean version and validated, which showed that Cronbach α coefficient for internal consistency of the total score of the PSQI was 0.84, and the test-retest correlation coefficient was 0.65 for the total score (P < 0.001).11
passing failure is an accident in which a train has run through a stop sign and skips a station at which it should stop. Mishandling failure is an accident in which a train is out of order because of mishandling of the train. Subjects were divided into two groups according to less than one error or one or more per 5 y of service career, which was defined as 5% of all train drivers from the statistical distribution of errors. Two questions were applied to assess the human errors of train drivers, “Have you experienced an accident?” and “How many times have you experienced things such as derailment, station passing failure, and mishandling failure while driving a train, except for railway death and injury?” Their career as train drivers was assessed by a question, “How long has your career as a train driver been?” The mean rate of human errors per year was calculated from the number of human errors divided by the length of the train driver’s career. Other Measures Demographic characteristics (age, education years, sex, and marital status) and duration of career as train drivers were obtained from the survey. The Center for Epidemiologic Studies Depression Scale (CES-D)12 was applied to evaluate the severity of depression. It is a 20-item questionnaire with a fivepoint scale used for assessing depressive symptomatology in the general population, and its Korean version also showed high reliability (Cronbach α = 0.893) and test-retest reliability (Pearson r coefficient, 0.68; P < 0.001) with cutoff at 21 points.13 The Impact of Event Scale-Revised (IES-R)14 was applied to measure posttraumatic stress over the lifetime. It is a 22-item self-rating scale of trauma-related symptoms including hyperarousal symptoms. Its Korean version also showed high reliability and validity for the assessment of PTSD symptom severity, and its cutoff score to indicate the experience of serious trauma was more than 25 points.15 The State-Trait Anxiety Inventory (STAI)16, which is a 20-item self-report instrument developed to assess levels of situation-related state anxiety (STAI-S) and trait anxiety (STAI-T), was applied to measure the severity of anxiety. The Korean version of STAI was validated.17 The Korean Occupational Stress Scale (KOSS)18 was applied to measure work stress. The KOSS was developed to evaluate unique and specific occupational stress in Korean employees.19 The questions for “exposure during train driving” consisted of “trouble with passengers,” “injury to passengers,” “death except for suicide,” and “completed suicide.”
Measure of Human Error Human errors of train drivers included derailment, station passing failure, and mishandling failure and did not include accidents involving railway deaths and injuries. This study was focused on human errors of train drivers, rather than on outcomes of the accidents themselves. Derailment is an accident in which a train comes off the track on which it is running. Station SLEEP, Vol. 37, No. 12, 2014
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Statistical Analysis Subjects were divided into two groups according to less than one error or one or more per 5 y of service career. The two groups were compared regarding age, sex, education years, marital status, number of human errors, career duration, depression, posttraumatic stress, trait and state anxiety, work stress, exposure during train driving, and total scores and sleep variables of the PSQI with Student t-test or chi-square test (two-tailed). Sleep efficiency (%) was calculated from the number of hours spent in bed divided by the number of hours slept. Two multiple logistic regression analyses were performed to evaluate associations with human errors as a dependent variable, after adjusting for age, sex, education years, marital status, and career duration. First, independent variables were sleep quality, sleep onset Sleep and Train Drivers—Jeon et al.
Table 1—Demographic and clinical profiles of train drivers according to experience of human errors. Human Errors of Train Drivers Profiles Age Education, years Number of human errors Career duration of train driving, years Trait anxiety a State anxiety b Work stress c Male sex Marital status Married Unmarried Divorced/separated/widowed Exposed during train driving Trouble with passengers Injury to passengers Death except for suicide Completed suicide Depression d Severe posttraumatic stress e
Statistics
Total (n = 4,634) Mean (SD) 45.3 (9.4) 13.0 (3.7) 0.9 (2.2) 17.4 (8.6) 34.8 (9.1) 35.4 (9.4) 46.7 (11.2)
≥ 1 error/5 y (n = 349) Mean (SD) 41.9 (7.2) 13.9 (3.3) 5.5 (5.4) 12.5 (7.7) 34.9 (9.0) 35.7 (9.4) 46.6 (12.2)
< 1 error/5 y (n = 4,285) Mean (SD) 45.8 (9.4) 12.9 (3.7) 0.5 (0.9) 18.1 (8.3) 34.8 (9.1) 35.4 (9.4) 46.7 (11.2)
t
P
7.7 5.3 16.0 12.2 0.3 0.5 0.1
< 0.0001 < 0.0001 < 0.0001 < 0.0001 0.79 0.61 0.94
n (%) 4,597 (99.2)
n (%) 342 (98.0)
n (%) 4,255 (99.3)
χ2 7.0
P 0.008
4,314 (93.1) 260 (5.6) 60 (1.3)
307 (88.0) 38 (10.9) 4 (1.1)
4,007 (93.5) 222 (5.2) 56 (1.3)
19.9
< 0.0001
371 (8.0) 795 (17.2) 1,076 (23.2) 1,471 (31.7) 202 (4.4) 599 (12.9)
68 (19.5) 88 (25.2) 95 (27.2) 103 (29.5) 30 (8.6) 86 (24.6)
303 (7.1) 707 (16.5) 981 (22.9) 1,368 (31.9) 172 (4.0) 513. (12.0)
67.5 17.3 3.4 0.9 16.3 46.0
< 0.0001 < 0.0001 0.07 0.35 < 0.0001 < 0.0001
State-Trait Anxiety Inventory-Trait (STAI-T). b State-Trait Anxiety Inventory-State (STAI-S). c Korean Occupational Stress Scale (KOSS). d Center for Epidemiologic Studies Depression Scale (CES-D) ≥ 21. e Impact of Event Scale-Revised (IES-R) ≥ 25. SD, standard deviation.
a
latency, sleep at night, sleep efficiency, and poor sleep quality; secondary variables were trait and state anxiety, work stress, depression, poor sleep quality, and severe posttraumatic stress. Statistical analysis was performed by using SPSS 17.0 (SPSS, Inc., Chicago), and the level of significance was set at P < 0.05. RESULTS Demographic and Clinical Profiles Of the 4,718 train drivers who participated in the survey, 84 were excluded because of an incomplete response. As a result, a total of 4,634 train drivers completed the interview (response rate 84.6%). The mean age of the subjects who completed the survey was 45.3 ± 9.4 y, with 13.0 ± 3.7 y of education, 99.2% male, and 93.1% married. Their mean service career as train drivers was 17.4 ± 8.6 y. Of the 4,634 train drivers who completed the questionnaires, the number of human errors was 0.06 times/y (standard deviation [SD] 0.02, minimum 0 and maximum 5). A total of 349 (7.5%) were classified into those who experienced one or more errors for every 5 y of service. Demographic and clinical profiles of the two groups are shown in Table 1. Train drivers with human errors (≥ 1 error/5 y) were younger, male, had more education years, short career duration, tended to be unmarried compared to those without human errors (< 1 error/5 y). Train drivers with human errors showed higher rates of depression and severe posttraumatic stress, and more exposure to trouble with passengers and injury of passengers than those without, SLEEP, Vol. 37, No. 12, 2014
whereas there were no significant differences in trait and state anxiety and work stress, and exposure to death except for suicide and completed suicide between the two groups. Sleep Quality, PSQI The mean score for the PSQI was 3.5 (SD 2.45, range 0 to 19), with 17.0% scoring above the cutoff value (> 5). The PSQI was compared between train drivers with and without ≥ 1 error/5 y of human errors (Table 2). Train drivers with human errors showed significantly higher scores on the PSQI total score (t = 6.2, P < 0.0001), sleep onset latency (t = 3.5, P < 0.0001), sleep duration at night (t = 3.1, P = 0.002), and poor sleep quality (χ2 = 37.0, P < 0.0001) than those without. No significant differences were found in sleep efficiency between the two groups (t = 0.6, P = 0.58).
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Posttraumatic Stress in Train Drivers With Poor Sleep Quality As shown in Figure 1, train drivers who had experienced poor sleep quality showed higher number of human errors than those who had not (degrees of freedom [df] = 904.7, t = 4.7, P < 0.001). Among those who had poor sleep quality, those who experienced severe traumatic stress showed significantly higher number of human errors than those who did not (df = 475.1, t = 2.3, P = 0.02). Multiple Logistic Regression Analyses for Human Errors The results of the multiple logistic regression analyses are shown in Table 3. Train drivers who committed human errors Sleep and Train Drivers—Jeon et al.
Table 2—Sleep quality and self-reported sleep variables according to experience of human errors. Human Errors of Train Drivers Profiles Sleep quality (PSQI total score) Sleep variables, by PSQI Sleep onset latency, min Sleep duration at night, h Sleep efficiency, % PSQI > 5 (poor sleep quality)
Statistics
Total (n = 4,634) Mean (SD) 3.5 (2.5)
≥ 1 error/5 y (n = 349) Mean (SD) 4.4 (3.0)
< 1 error/5 y (n = 4,285) Mean (SD) 3.4 (2.4)
t
P
6.2
< 0.0001
20.7 (17.0) 6.8 (1.2) 86.8 (13.6)
24.1 (18.8) 6.6 (1.2) 87.2 (13.8)
20.5 (16.9) 6.8 (1.2) 86.8 (13.6)
3.5 3.1 0.6
< 0.0001 0.002 0.58
n (%) 792 (17.0)
n (%) 100 (29.0)
n (%) 685 (16.2)
χ2 37.0
P < 0.0001
PSQI, Pittsburgh Sleep Quality Index, SD, standard deviation.
Table 3—Multiple logistic regression analysis of human errors for sleep quality and trauma experience. More Than One Human Error Per 5 y Profiles Trait anxiety a State anxiety b Work stress c Depression d Poor sleep quality e Severe posttraumatic stress f
AOR (95% CI) 1.0 (1.0-1.0) 1.0 (1.0-1.0) 1.0 (1.0-1.0) 1.3 (0.8-2.0) 1.7 (1.3-2.2) 2.2 (1.6-2.9)
P 1.0 0.5 0.4 0.3 < 0.001 < 0.001
Analysis adjusted for age, sex, education years, marital status, and career duration. a Measured by the State-Trait Anxiety Inventory-Trait (STAI-T). b State-Trait Anxiety Inventory-State (STAI-S). c Korean Occupational Stress Scale (KOSS). d Center for Epidemiologic Studies Depression Scale (CES-D) ≥ 21. e Pittsburgh Sleep Quality Index (PSQI) > 5. f Impact of Event Scale-Revised (IES-R) ≥ 25. AOR, adjusted odds ration; CI, confidence interval.
Figure 1—Poor sleep quality and human errors with and without experience of severe posttraumatic stress in train drivers of South Korea (n = 4,634). Exposure to severe posttraumatic stress was defined as 25 or higher scores of the Impact of Event Scale-Revised (IES-R). CI, confidence interval.
were significantly associated with poor sleep quality (AOR [adjusted odds ratio] = 1.7, 95% confidence interval [CI] 1.3-2.2) and posttraumatic stress (AOR = 2.2, 95% CI 1.6-2.9), whereas there were no significant associations with depression, trait and state anxiety, and work stress after adjusting for age, sex, education years, marital status, and career duration. DISCUSSION This is the first study from a large population-based survey to investigate an association between sleep quality and human errors according to the experience of posttraumatic stress. The main finding of this study is that poor sleep quality was associated with more human errors in train drivers, especially in those who experienced serious posttraumatic stress. Human SLEEP, Vol. 37, No. 12, 2014
errors were associated with both sleep quality and posttraumatic stress after adjusting for age, sex, education years, marital status, trait anxiety, state anxiety, work stress, and depression. This study showed that poor sleep quality is a common condition among train drivers. A total of 17.0% of train drivers suffer from poor sleep quality, which was assessed as being present when scores were greater than 5 points on the PSQI total score. Although there are no previous studies of prevalence of poor sleep in train drivers, this figure is less frequent than 26.4% of the general Japanese male adult population20 and 26.5% of the Austrian male population,21 and 30.03% of the population in the German Health Survey.22 This study also showed that the rate of poor sleep quality was 1.7 times higher among train drivers who experienced more human errors than those who had not. In addition, we found that train drivers with human errors showed poor sleep quality, higher PSQI total scores, short sleep at night, and longer sleep latency than those without errors, but no significant differences were found in sleep efficiency. Shahly et al.23 estimated that insomnia was associated with 7.2% of all costly workplace accidents and errors and one-fourth of all the costs of these incidents.
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An important finding of this study is that poor sleep quality is more strongly associated with human errors in those who experienced serious posttraumatic stress than in those who did not. Train drivers handle a large vehicle with many passengers and continue their work throughout their life, so they commonly experience traumatic accidents such as trouble with passengers, or injury and death of passengers including suicides by patients jumping in front of a running train. Notably, this study indicated that train drivers commonly experience these issues, and suffer from posttraumatic stress, which was related to human errors along with sleep quality. In previous studies, prevalence rates of PTSD were 16–17% among train drivers experiencing “person under the train” incidents.24 PTSD can be diagnosed if a person is exposed to one or more life-threatening events, and a group of symptoms such as re-experiencing the events in nightmares and having disturbing recurring flashbacks, having an avoidance pattern of behavior or having numbing of the memories of the event; and experiencing hyperarousal symptoms that continue for more than 1 mo after the traumatic event.25 Previous studies revealed that the symptoms of PTSD have a bidirectional influence on poor sleep quality.8,26 PTSD involves deficits in information processing that may reflect hypervigilance and deficient inhibitory control,27 and co-occurrence with major depressive disorder increases the risk for suicidal behavior.28 PTSD is commonly associated with alcohol dependence, which is associated with high levels of severity.29 Among the types of posttraumatic stress, train drivers who experienced trouble with passengers or injury of passengers committed more errors than those who experienced death except for attempted suicide and completed suicide. This finding suggests that stress associated with human errors may be related to errors that are within the drivers’ personal responsibility. Accidental death and suicide are serious traumatic experiences to the general population, but the drivers themselves are usually not responsible for these events. These results suggest that the subjective perception of the severity of the trauma may be important in producing posttraumatic stress, poor sleep quality, and human errors in train drivers. Train drivers with posttraumatic stress worried about being involved in accidents and showed the most symptoms of distress, and sometimes they suffered from long-term psychological distress.30 Although depression was also associated with human errors, no significance was found after controlling for poor sleep quality. This finding indicates that human errors are more strongly related to poor sleep quality than depression, although poor sleep quality is one of the diagnostic criteria of major depression.25 Both trait and state anxiety showed no significant association with human errors. As a previous study reported that optimal anxiety can boost early error detection mechanisms,31 this study revealed that anxiety was not significantly associated with human errors. This study revealed that work stress also showed no association with human errors, although a previous study reported that work stress is strongly linked to disturbed sleep and impaired awakening in the general population.32 The human errors in this study were measured throughout the career duration of train drivers as a state variable, whereas sleep, depression, anxiety, and work stress were measured within 1 mo or 1 w as trait variables. It suggested that current sleep quality of train drivers is associated with state of human errors of train drivers. SLEEP, Vol. 37, No. 12, 2014
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The train drivers with more human errors had less train driving experience than those with fewer errors. Less experience is associated with greater crash risk in other transportation modes such as motor vehicle driving. Although posttraumatic stress can create poor sleep quality - and therefore significantly more train errors - it may be that a relative lack of experience that explains the increased rate of errors in these train drivers. Still, the train drivers with more errors did have more than 10 y of experience, so we think that lack of experience is unlikely to account for the increased error rate. Nonetheless, this cannot be completely addressed with the current data and further study is needed to evaluate this issue. Despite its strengths, such as the large sample size of a homogenous group, there are several limitations to this study that should be considered when interpreting the findings. First, this is a cross-sectional survey in which information about sleep, posttraumatic stress, and depression was based on retrospective reports. Therefore, recall bias may have affected the accuracy of the responses to the questionnaires.33 Second, false negatives in the results of the questionnaires may have underestimated the real rates of human errors and posttraumatic stress. Thus, it is possible that these data underestimate the number of human errors, as information about the number of human errors was obtained through self-reporting rather than from the database of the train company. To reduce underreporting of errors and symptoms, we made every effort to ensure confidentiality of the participants, such as using an external server system with higher security and data encryption, and no provision of subjects’ personal identification and data was made to their train company, which was explained to them before starting the interview. Third, nonresponsiveness to the interview also may have impacted these results, as it has been reported that nonrespondents have higher rates of mental disorders than respondents.34,35 Fourth, further study is needed to consider medical illness and medications for depression, anxiety, insomnia, and somnolence in train drivers. We plan to establish a mental health promotion system for train drivers. In conclusion, we found that poor sleep quality and posttraumatic stress are associated with human errors of train drivers. Poor sleep quality is more strongly associated with increased human errors in train drivers, especially those who experienced severe posttraumatic stress than those who did not. These findings suggest that it is important to reduce human errors and ultimately prevent railway disasters for train drivers by improving sleep quality, especially for train drivers who have experienced posttraumatic stress. ACKNOWLEDGMENTS The authors thank the Samsung Statistical Support Team, chief Dr. Seon-Woo Kim, for statistical support. DISCLOSURE STATEMENT This study was supported by the Korean National Railroad Corporation (KORAIL). This study was also supported by the Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Education, Science and Technology (No. 2011-0013064), and the Samsung Medical Center Clinical Research Development Program (CRDP) Grant SMO1131461. Dr. Fava has received Sleep and Train Drivers—Jeon et al.
research support from Abbott Laboratories, Alkermes, Aspect Medical Systems, Astra-Zeneca, BioResearch, BrainCells, Inc., Bristol-Myers Squibb Company, Cephalon, Clinical Trial Solutions, LLC, Eli Lilly & Company, EnVivo Pharmaceuticals, Inc., Forest Pharmaceuticals Inc., Ganeden, GlaxoSmithKline, J & J Pharmaceuticals, Lichtwer Pharma GmbH, Lorex Pharmaceuticals, NARSAD, NCCAM, NIDA, NIMH, Novartis, Organon Inc., PamLab, LLC, Pfizer Inc., Pharmavite, Roche, SanofiAventis, Shire, Solvay Pharmaceuticals, Inc., Synthelabo, and Wyeth-Ayerst Laboratories. He has served as an advisor and consultant to Abbott Laboratories, Affectis Pharmaceuticals AG, Amarin, Aspect Medical Systems, Astra-Zeneca, Auspex Pharmaceuticals, Bayer AG, Best Practice Project Management, Inc., BioMarin Pharmaceuticals, Inc., Biovail Pharmaceuticals, Inc., BrainCells, Inc., Bristol-Myers Squibb Company, Cephalon, Clinical Trials Solutions, LLC, CNS Response, Compellis, Cypress Pharmaceuticals, Dov Pharmaceuticals, Eisai, Inc., Eli Lilly & Company, EPIX Pharmaceuticals, Euthymics Bioscience, Inc., Fabre-Kramer, Pharmaceuticals, Inc., Forest Pharmaceuticals Inc., GlaxoSmithKline, Grunenthal GmBH, Janssen Pharmaceutica, Jazz Pharmaceuticals, J & J Pharmaceuticals, Knoll Pharmaceutical Company, Labopharm, Lorex Pharmaceuticals, Lundbeck, MedAvante Inc., Merck, Methylation Sciences, Neuronetics, Novartis, Nutrition 21, Organon Inc., PamLab, LLC, Pfizer Inc., PharmaStar, Pharmavite, Precision Human Biolaboratory, Prexa Pharmaceuticals, Inc., PsychoGenics, Psylin Neurosciences, Inc., Ridge Diagnostics, Inc., Roche, Sanofi-Aventis, Sepracor, Schering-Plough, Solvay Pharmaceuticals, Inc., Somaxon, Somerset Pharmaceuticals, Synthelabo, Takeda, Tetragenex, TransForm Pharmaceuticals, Inc., Transcept Pharmaceuticals, Vanda Pharmaceuticals Inc., Wyeth-Ayerst Laboratories. He has received speaking and publishing honoraria from Adamed, Co., Advanced Meeting Partners, American Psychiatric Association, American Society of Clinical Psychopharmacology, Astra-Zeneca, Belvoir, Boehringer-Ingelheim, Bristol-Myers Squibb Company, Cephalon, Eli Lilly & Company, Forest Pharmaceuticals Inc., GlaxoSmithKline, Imedex, Novartis, Organon Inc., Pfizer Inc., PharmaStar, MGH Psychiatry Academy/Primedia, MGH Psychiatry Academy/Reed-Elsevier, UBC, and Wyeth-Ayerst Laboratories. He holds equity in Compellis. He currently holds a patent for SPCD and a patent application for a combination of azapirones and bupropion in MDD, and has received copyright royalties for the MGH CPFQ, SFI, ATRQ, DESS, and SAFER diagnostic instruments. Dr Mischoulon has received research support from the Bowman Family Foundation, FisherWallace, Ganeden, Nordic Naturals, and Methylation Sciences, Inc. (MSI). He has received honoraria for consulting, speaking, and writing from the Massachusetts General Hospital Psychiatry Academy. He has received royalties from Lippincott Williams & Wilkins for published book “Natural Medications for Psychiatric Disorders: Considering the Alternatives.” The other authors have indicated no financial conflicts of interest. The work was performed at Samsung Medical Center, Sungkyunkwan University School of Medicine, Seoul, Korea. REFERENCES
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