The effect of daylight versus darkness on driver sleepiness: a driving simulator study

Driver sleepiness studies are often carried out with alert drivers during daytime and sleep‐deprived drivers during night‐time. This design results in a mixture of different factors (e.g. circadian effects, homeostatic effects, light conditions) that may confound the results. The aim of this study was to investigate the effect of light conditions on driver sleepiness. Thirty young male drivers (23.6 ± 1.7 years old) participated in a driving simulator experiment where they drove on a rural road. A 2 × 2 design was used with the conditions daylight versus darkness, and daytime (full sleep) versus night‐time (sleep deprived). The results show that light condition had an independent effect on the sleepiness variables. The subjective sleepiness measured by Karolinska Sleepiness Scale was higher, lateral position more left‐oriented, speed lower, electroencephalogram alpha and theta higher, and blink durations were longer during darkness. The number of line crossings did not change significantly with light condition. The day/night condition had profound effects on most sleepiness indicators while controlling for light condition. The number of line crossings was higher during night driving, Karolinska Sleepiness Scale was higher, blink durations were longer and speed was lower. There were no significant interactions, indicating that light conditions have an additive effect on sleepiness. In conclusion, Karolinska Sleepiness Scale and blink durations increase primarily with sleep deprivation, but also as an effect of darkness. Line crossings are mainly driven by the need for sleep and the reduced alertness at the circadian nadir. Lane position is, however, more determined by light conditions than by sleepiness.     

Having to stop driving at night because of dangerous sleepiness – awareness,physiology and behaviour

A large number of accidents are due to the driver falling asleep at the wheel, but details of this link have not been studied on a real road. The purpose of the present study was to describe the development of sleepiness indicators, leading to the drive being terminated prematurely by the onboard expert driving instructor because of imminent danger. Eighteen individuals participated during a day drive and a night drive on a motorway (both 90 min). Eight drivers terminated (N) prematurely (after 43 min) because of sleep‐related imminent danger [according to the driving instructor or their own judgement (two cases)]. The results showed very high sleepiness ratings (8.5 units on the Karolinska Sleepiness Scale) immediately before termination (<7 at a similar time interval for those 10 who completed the drive). Group N also showed significantly higher levels of sleep intrusions on the electroencephalography/electro‐oculography (EEG/EOG) than those who completed the drive (group C). The sleep intrusions were increased in group N during the first 40 min of the night drive. During the day drive, sleep intrusions were increased significantly in group N. The night drive showed significant increases of all sleepiness indicators compared to the day drive, but also reduced speed and driving to the left in the lane. It was concluded that 44% of drivers during late‐night driving became dangerously sleepy, and that this group showed higher perceived sleepiness and more sleep intrusions in the EEG/EOG.     

Ecological momentary assessment of daytime symptoms during sleep restriction therapy for insomnia

This study profiles changes in self‐reported daytime functioning during sleep restriction therapy (SRT) for insomnia. Ecological momentary assessment (EMA) captured point‐in‐time symptomatology to map the time–course of symptoms. We hypothesized a deterioration (week 1) followed by improvements at week 3 of therapy relative to baseline. Nine patients with psychophysiological insomnia completed the Daytime Insomnia Symptom Scale (DISS) at rise‐time, 12:00 hours, 18:00 hours and bedtime for 1 week before and 3 weeks during SRT. Four validated factors from the DISS were analyzed (alert cognition, positive mood, negative mood and sleepiness/fatigue) across 28 days yielding 17 170 data points. Factors evaluated week (baseline versus weeks 1 and 3) and time of day symptomatology. Insomnia Severity Index scores decreased significantly pre‐to‐post treatment (mean 18 versus 7). Reflecting acute effects of SRT, significant differences were found for all factors, except negative mood, between baseline and week 1 of SRT, suggesting adverse effects. By week 3, sleepiness/fatigue and negative mood decreased significantly compared to baseline, and positive mood showed a trend towards improvement (P = 0.06). Sleepiness/fatigue displayed a significant week × time of day interaction, explained by a reduction in sleepiness/fatigue at every daytime assessment point (except bedtime, which remained high). A significant interaction for alert cognition was associated with reduction in alertness at bedtime by week 3 and an increase in alertness at rise‐time, suggesting that SRT not only improves sleep, but moderates alertness and sleepiness in therapeutic ways. Initial SRT is associated with an increase in sleepiness/fatigue and a decrease in alert cognition.     

An experimental study of adolescent sleep restriction during a simulated school week: changes in phase,sleep staging,performance and sleepiness

This laboratory study investigated the impact of restricted sleep during a simulated school week on circadian phase, sleep stages and daytime functioning. Changes were examined across and within days and during a simulated weekend recovery. Participants were 12 healthy secondary school students (six male) aged 15–17 years [mean = 16.1 years, standard deviation (SD) = 0.9]. After 2 nights with 10 h (21:30–07:30 hours), time in bed was restricted to 5 h for 5 nights (02:30–07:30 hours), then returned to 10 h time in bed for 2 nights (21:30–07:30 hours). Saliva was collected in dim light on the first and last sleep restriction nights to measure melatonin onset phase. Sleep was recorded polysomnographically, and the Psychomotor Vigilance Task (PVT) and Karolinska Sleepiness Scale were undertaken 3‐hourly while awake. Average phase delay measured by melatonin was 3 h (SD = 50 min). Compared to baseline, sleep during the restriction period contained a smaller percentage of Stages 1 and 2 and rapid eye movement (REM) and a greater percentage of Stage 4. PVT lapses increased significantly during sleep restriction and did not return to baseline levels during recovery. Subjective sleepiness showed a similar pattern during restriction, but returned to baseline levels during recovery. Results suggest that sustained attention in adolescents is affected negatively by sleep restriction, particularly in the early morning, and that a weekend of recovery sleep is insufficient to restore performance. The discrepancy between sleepiness ratings and performance may indicate a lack of perception of this residual impairment.     

Effects of sleep/wake history and circadian phase on proposed pilot fatigue safety performance indicators

The Karolinska Sleepiness Scale and Samn–Perelli fatigue ratings, and psychomotor vigilance task performance are proposed as measures for monitoring commercial pilot fatigue. In laboratory studies, they are sensitive to sleep/wake history and circadian phase. The present analyses examined whether they reliably reflect sleep/wake history and circadian phase during transmeridian flight operations. Data were combined from four studies (237 pilots, 730 out‐and‐back flights between 13 city pairs, 1–3‐day layovers). Sleep was monitored (wrist actigraphy, logbooks) before, during and after trips. On duty days, sleepiness, fatigue and mean response speed were measured pre‐flight and at the top of the descent. Mixed‐model analysis of variance examined associations between these measures and sleep/wake history, after controlling for operational factors. Circadian phase was approximated by local (domicile) time in the city where each trip began and ended. More sleep in the 24 h prior to duty was associated with lower pre‐flight sleepiness and fatigue and faster response speed. Sleepiness and fatigue were greater before flights departing during the domicile night and early morning. At the top of the descent, pilots felt less sleepy and fatigued after more in‐flight sleep and less time awake. Flights arriving in the early–mid‐morning (domicile time) had greater sleepiness and fatigue and slower response speeds than flights arriving later. Subjective ratings showed expected associations with sleep/wake history and circadian phase. The response speed showed expected circadian variation but was not associated with sleep/wake history at the top of the descent. This may reflect moderate levels of fatigue at this time and/or atypically fast responses among pilots.     

Definition of excessive daytime sleepiness in the general population: Feeling sleepy relates better to sleep‐related symptoms and quality of life than the Epworth Sleepiness Scale score. Results from an epidemiological study

Many different subjective tools are being used to measure excessive daytime sleepiness (EDS) but the most widely used is the Epworth Sleepiness Scale (ESS). However, it is unclear if using the ESS is adequate on its own when assessing EDS. The aim of this study was to estimate the characteristics and prevalence of EDS using the ESS and the Basic Nordic Sleep Questionnaire (BNSQ) in general population samples. Participants aged 40 years and older answered questions about sleepiness, health, sleep‐related symptoms and quality of life. Two groups were defined as suffering from EDS: those who scored >10 on the ESS (with increased risk of dozing off) and those reporting feeling sleepy during the day ≥3 times per week on the BNSQ. In total, 1,338 subjects (53% male, 74.1% response rate) participated, 13.1% reported an increased risk of dozing off, 23.2% reported feeling sleepy and 6.4% reported both. The prevalence of restless leg syndrome, nocturnal gastroesophageal reflux, difficulties initiating and maintaining sleep and nocturnal sweating was higher among subjects reporting feeling sleepy compared to non‐sleepy subjects. Also, subjects reporting feeling sleepy had poorer quality of life and reported more often feeling unrested during the day than non‐sleepy subjects. However, subjects reporting increased risk of dozing off (ESS > 10) without feeling sleepy had a similar symptom profile as the non‐sleepy subjects. Therefore, reporting only risk of dozing off without feeling sleepy may not reflect problematic sleepiness and more instruments in addition to ESS are needed when evaluating daytime sleepiness.     

Subjective sleepiness is a sensitive indicator of insufficient sleep and impaired waking function

The main consequence of insufficient sleep is sleepiness. While measures of sleep latency, continuous encephalographical/electro‐oculographical (EEG/EOG) recording and performance tests are useful indicators of sleepiness in the laboratory and clinic, they are not easily implemented in large, real‐life field studies. Subjective ratings of sleepiness, which are easily applied and unobtrusive, are an alternative, but whether they measure sleepiness sensitively, reliably and validly remains uncertain. This review brings together research relevant to these issues. It is focused on the Karolinska Sleepiness Scale (KSS), which is a nine‐point Likert‐type scale. The diurnal pattern of sleepiness is U‐shaped, with high KSS values in the morning and late evening, and with great stability across years. KSS values increase sensitively during acute total and repeated partial sleep deprivation and night work, including night driving. The effect sizes range between 1.5 and 3. The relation to driving performance or EEG/EOG indicators of sleepiness is highly significant, strongly curvilinear and consistent across individuals. High (>6) KSS values are associated particularly with impaired driving performance and sleep intrusions in the EEG. KSS values are also increased in many clinical conditions such as sleep apnea, depression and burnout. The context has a strong influence on KSS ratings. Thus, physical activity, social interaction and light exposure will reduce KSS values by 1–2 units. In contrast, time‐on‐task in a monotonous context will increase KSS values by 1–2 units. In summary, subjective ratings of sleepiness as described here is as sensitive and valid an indicator of sleepiness as objective measures, and particularly suitable for field studies.     

The daily variation in sleepiness and its relation to the preceding sleep episode—a prospective study across 42 days of normal living

Sleepiness is linked to accidents and reduced performance, and is usually attributed to short/poor prior sleep and sleepiness. However, while the link between reduced sleep and subsequent sleepiness is well established in laboratory experiments of sleep reduction, very little is known about the day‐to‐day variation of sleepiness in everyday life and its relation to the immediately preceding sleep episode. The purpose of the present study was to investigate the characteristics of this relation across 42 consecutive days. Fifty volunteers participated. Self‐reports of sleep were given in the morning and recorded with actigraphy; health was rated in the evening; and sleepiness was rated at eight points during the day (on a scale of 1–9). Results from mixed‐model regression analyses showed that, on average, total sleep time predicted sleepiness during the rest of the day across the 42 days, with sleepiness increasing with shorter preceding sleep (β = ?0.15 units h^?1, P < 0.001). Sleepiness also increased with earlier time of rising and lower‐rated sleep quality. Days off reduced sleepiness, but was accounted for by sleep. Self‐rated health improved when sleepiness was low during the same day (β = ?0.36 unit unit^?1 of rated health, P < 0.001), but the two were measured simultaneously. Napping was related to high sleepiness during the same day. Actigraphy measures of sleep duration showed similar, but somewhat weaker, effects than diary measures. It was concluded that the main determinants of daytime sleepiness in a real‐life day‐to‐day context were short sleep, poor sleep and early rising, and that days with high sleepiness ended with ratings of poorer health.     

Daytime course of sleepiness in de novo Parkinson's disease patients

Normal subjects show an increase of sleepiness in the morning, early afternoon and before sleep. In the advanced stages of Parkinson's disease (PD) the mean level of sleepiness is quite high, while with respect to healthy subjects it seems to be unchanged in the early stages. The aim of this study was to evaluate the time–course of the sleepiness level during the wakefulness period in untreated patients with early‐stage Parkinson's disease. Eighteen Parkinson's disease patients who had never been treated before with dopaminergic drugs (male = 9, female = 9, age: 68.39 ± 1.89, mean ± standard error) and 18 healthy subjects (male = 9, female = 9, age: 67.22 ± 1.98) were recruited for this study. All subjects underwent continuous actigraphic recording for three consecutive days, during which they also completed the Karolinska Sleepiness Scale (KSS) once an hour throughout wakefulness. Our results showed a higher level of sleepiness in the patients than the controls in the hours following awakening and in the early afternoon, specifically at 08:00 and 14:00 hours (08:00 hours, PD patients, KSS: 3 ± 0.3 versus healthy subjects, KSS: 2 ± 0.2, P < 0.05; 14:00 hours, PD patients, KSS: 4.4 ± 0.5 versus healthy subjects, KSS: 3 ± 0.3, P < 0.05). We suggest that some daytime hours are sensitive windows showing the first increase of sleepiness which will spread later to the whole daytime.     

Sleep habits and accident risk among truck drivers: a cross-sectional study in Argentina

Road accidents are a major cause of death, and sleep deprivation affects driving skills. We conducted a cross-sectional study to evaluate sleep habits and accident risk in long-haul truck drivers in Buenos Aires, Argentina. Questionnaires regarding sleep habits, snoring, and daytime sleepiness were administered, and a limited physical examination was performed. We obtained 738 complete answers (response rate 85%). Mean sleep hours during working days was 3.76 (SD 2.40). Mean driving hours was 15.9 (SD 5.60) per day. Frequent sleepiness while driving was reported by 43.7% of responders. Sleepiness while driving was associated with Epworth Sleepiness Scale values >10 (odds ratio 1.85, 95% confidence interval = 1.20-2.85). Snoring was reportea by 71% of drivers and was frequent in 43.8%. Snoring more than 3 times a week (odds ratio 1.73, 95% confidence interval = 1.23-2.44), sleepiness while driving (OR 1.92, 95% confidence interval = 1.08-1.96), and Epworth Sleepiness Scale score > 10 (odds ratio 2.53, 95% confidence interval = 1.61-3.97) were independently associated with reporting of accidents or near accidents. Sleep deprivation and long driving shifts were prevalent in our study. Accident risk was associated with frequent snoring, daytime sleepiness, and reporting of sleepiness at the wheel. This study highlights the need of improving working conditions in this highly exposed population.     

In‐flight sleep,pilot fatigue and Psychomotor Vigilance Task performance on ultra‐long range versus long range flights

This study evaluated whether pilot fatigue was greater on ultra‐long range (ULR) trips (flights >16 h on 10% of trips in a 90‐day period) than on long range (LR) trips. The within‐subjects design controlled for crew complement, pattern of in‐flight breaks, flight direction and departure time. Thirty male Captains (mean age = 54.5 years) and 40 male First officers (mean age = 48.0 years) were monitored on commercial passenger flights (Boeing 777 aircraft). Sleep was monitored (actigraphy, duty/sleep diaries) from 3 days before the first study trip to 3 days after the second study trip. Karolinska Sleepiness Scale, Samn–Perelli fatigue ratings and a 5‐min Psychomotor Vigilance Task were completed before, during and after every flight. Total sleep in the 24 h before outbound flights and before inbound flights after 2‐day layovers was comparable for ULR and LR flights. All pilots slept on all flights. For each additional hour of flight time, they obtained an estimated additional 12.3 min of sleep. Estimated mean total sleep was longer on ULR flights (3 h 53 min) than LR flights (3 h 15 min; P(F) = 0.0004). Sleepiness ratings were lower and mean reaction speed was faster at the end of ULR flights. Findings suggest that additional in‐flight sleep mitigated fatigue effectively on longer flights. Further research is needed to clarify the contributions to fatigue of in‐flight sleep versus time awake at top of descent. The study design was limited to eastward outbound flights with two Captains and two First Officers. Caution must be exercised when extrapolating to different operations.     

Effects of long working hours and the night shift on severe sleepiness among workers with 12‐hour shift systems for 5 to 7 consecutive days in the automobile factories of Korea

We investigated the effects of 12‐hour shift work for five to seven consecutive days and overtime on the prevalence of severe sleepiness in the automobile industry in Korea. [Correction added after online publication 28 Nov: Opening sentence of the summary has been rephrased for better clarity.] A total of 288 randomly selected male workers from two automobile factories were selected and investigated using questionnaires and sleep‐wake diaries in South Korea. The prevalence of severe sleepiness at work [i.e. Karolinska Sleepiness Scale (KSS) score of 7 or higher] was modeled using marginal logistic regression and included theoretical risk factors related to working hours and potential confounding factors related to socio‐economic status, work demands, and health behaviors. Factors related to working hours increased the risk for severe sleepiness at the end of the shift in the following order: the night shift [odds ratio (OR): 4.7; 95% confidence interval (CI): 3.6–6.0)], daily overtime (OR: 2.2; 95% CI: 1.7–2.9), weekly overtime (OR: 1.6; 95% CI: 1.0–2.6), and night overtime (OR: 1.6; 95% CI: 0.8–3.0). Long working hours and shift work had a significant interactive effect for severe sleepiness at work. Night shift workers who worked for 12 h or more a day were exposed to a risk of severe sleepiness that was 7.5 times greater than day shift workers who worked less than 11 h. Night shifts and long working hours were the main risk factors for severe sleepiness among automobile factory workers in Korea. Night shifts and long working hours have a high degree of interactive effects resulting in severe sleepiness at work, which highlight the need for immediate measures to address these characteristics among South Korean labor force patterns.     

Sharp and sleepy: evidence for dissociation between sleep pressure and nocturnal performance

While sleep restriction decreases performance, not all individuals are equal with regard to sensitivity to sleep loss. We tested the hypothesis that performance could be independent of sleep pressure as defined by EEG alpha-theta power. Twenty healthy subjects (10 vulnerable and 10 resistant) underwent sleep deprivation for 25 h. Subjects had to rate their sleepiness (Karolinska Sleepiness Scale) and to perform a 10-min psychomotor vigilance task (PVT) every 2 h (20:00-08:00 hours). Sleep pressure was measured by EEG power spectral analysis (alpha-theta band 6.0-9.0 Hz). Initial performance, EEG spectral power and KSS score were equal in both groups (ANOVA, NS). The performance of vulnerable subjects significantly increased during the night (rANOVA, P < 0.01), whereas resistant subjects globally sustained their performance. Homeostatic pressure and subjective sleepiness significantly increased during the night (rANOVA, P < 0.01) identically in both categories (rANOVA, NS). Resistant subjects sustained their reaction time independently of the increase in homeostatic pressure. The phenotypic determinants of vulnerability to extended wakefulness remain unknown.     

Sleep and sleepiness in young individuals with high burnout scores

STUDY OBJECTIVES: Burnout is a growing health problem in Western society. This study aimed to investigate sleep in subjects scoring high on burnout but still at work. The purpose was also to study the diurnal pattern of sleepiness, as well as ratings of work stress and mood in groups with different burnout scores. DESIGN: Sleep was recorded in 2 groups (high vs low on burnout) during 2 nights; 1 before a workday and 1 before a day off, in a balanced order. Sleepiness ratings as well as daytime diary ratings were analyzed for the workday and the day off after the sleep recordings. SETTING: The polysomnographic recordings were made in the subjects' home. PARTICIPANTS: Twenty-four healthy individuals (14 women and 10 men) between the ages of 24 and 43 years participated. INTERVENTIONS: N/A. MEASUREMENTS AND RESULTS: A higher frequency of arousals during sleep (Workday: high burnout = 12+/-1 per hour, low burnout = 8+/-1 per hour; Day off: high burnout = 12+/-2 per hour, low burnout =8+/-1 per hour), and more subjective awakening problems were found in the high-burnout group. The diurnal pattern of sleepiness indicated that the high-burnout group did not recover in the same way as did the low-burnout group on the day off. Indicators of impaired recovery were also seen within the high-burnout group as a higher degree of bringing work home and working on weekends, as well as more complaints of work interfering with leisure time. CONCLUSIONS: Young subjects with high burnout scores, but who are still working, show more arousals during sleep and an absence of reduced sleepiness during days off.     

Subjective and objective measures of adaptation and readaptation to night work on an oil rig in the North Sea

STUDY OBJECTIVES: To study the adaptation and readaptation processes to 1 week of night work (6:30 PM to 6:30 AM) followed by 1 week of day work (6:30 AM to 6:30 PM). DESIGN: Part of a randomized, placebo-controlled, crossover field study. Here, data from the placebo arm are presented. SETTING: Oil rig in the North Sea. Work schedule: 2 weeks on a 12-hour shift, with the first week on the night shift and the second week on the day shift. PARTICIPANTS: Subjects complaining about problems with adjusting to shift work. Seventeen workers completed the study. INTERVENTIONS: N/A. MEASUREMENTS: Subjective and objective measures of sleepiness (Karolinska Sleepiness Scale and simple serial reaction time test) and sleep (diary and actigraphy). RESULTS: Both subjective and objective measures improved gradually during night work. The return to day work after 1 week on the night shift led to a clear increase in subjective sleepiness and worsening of sleep parameters. During the week on the day shift, sleepiness and sleep gradually improved, similar to the improvement seen during night work. The workers indicated that the day shift was worse than the night shift on some of the measures, e.g., sleep length was significantly longer during the night-shift period. CONCLUSIONS: This is one of few studies showing how shift workers in a real-life setting adjust to night work. Both subjective and objective sleepiness and subjective sleep improved across days. The effects were especially pronounced for the subjective data.     

Sleep quality of German soldiers before,during and after deployment in Afghanistan—a prospective study

In this prospective study, subjective sleep quality and excessive daytime sleepiness prior to, during and after deployment of German soldiers in Afghanistan were examined. Sleep quality (Pittsburgh Sleep Quality Index; PSQI) and daytime sleepiness (Epworth Sleepiness Scale; ESS) were assessed in 118 soldiers of the German army, who were deployed in Afghanistan for 6 months (deployment group: DG) and in 146 soldiers of a non‐deployed control group (CG) at baseline. Results of the longitudinal analysis are reported, based on assessments conducted prior to, during the deployment and afterwards in the DG, and in the CG in parallel. Sleep quality and daytime sleepiness in the DG were already impaired during the predeployment training phase and remained at that level during the deployment phase, which clearly indicates the need for more attention on sleep in young soldiers, already at this early stage. The percentage of impaired sleepers decreased significantly after deployment. Programmes to teach techniques to improve sleep and reduce stress should be implemented prior to deployment to reduce sleep difficulties and excessive daytime sleepiness and subsequent psychiatric disorders.     

Self-reported ‘sleep deficit’ is unrelated to daytime sleepiness

Seemingly, many healthy adults have accrued a sleep debt, as determined by findings based on the multiple sleep latency test (MSLT). However, our recent, extensive survey found self-reported sleep deficit was not linked to daytime sleepiness determined by the Epworth sleepiness scale (ESS). Here, we report on the link between self-reported sleep deficit and gold standard measures of sleepiness: MSLT, Psychomotor vigilance test (PVT) and Karolinska Sleepiness Scale (KSS). Habitual sleep time in forty-three participants, from using a week long sleep diary and actiwatch data, compared with self-ratings of how much sleep they needed, provided estimates of apparent sleep deficit or otherwise. They were split into categories: ‘sleep deficit’ (Av. ? 47 min), ‘sleep plus’ (Av. 47 min) or ‘neutral’ (Av. 0 ± 15 min), depicting perceived shortfall (or excess) sleep. Although the deficit group desired to sleep longer than the other groups, they actually obtained similar habitual nightly sleep as the neutral group, but less than the sleep plus group. ‘Survival curves’ based on those falling asleep during the MSLT showed no difference between the groups. Neither was there any difference between the groups for the PVT, KSS, or ESS. Here, factors other than sleepiness seem to influence self-perceived sleep deficits.     

Subjective sleepiness, simulated driving performance and blink duration: examining individual differences

The present study aimed to provide subject-specific estimates of the relation between subjective sleepiness measured with the Karolinska Sleepiness Scale (KSS) and blink duration (BLINKD) and lane drifting calculated as the standard deviation of the lateral position (SDLAT) in a high-fidelity moving base driving simulator. Five male and five female shift workers were recruited to participate in a 2-h drive (08:00-10:00 hours) after a normal night sleep and after working a night shift. Subjective sleepiness was rated on the KSS in 5-min intervals during the drive, electro-occulogram (EOG) was measured continuously to calculate BLINKD, and SDLAT was collected from the simulator. A mixed model anova showed a significant (P < 0.001) effect of the KSS for both dependent variables. A test for a quadratic trend suggests a curvilinear effect with a steeper increase at high KSS levels for both SDLAT (P < 0.001) and BLINKD (P = 0.003). Large individual differences were observed for the intercept (P < 0.001), suggesting that subjects differed in their overall driving performance and blink duration independent of sleepiness levels. The results have implications for any application that needs prediction at the subject level (e.g. driver fatigue warning systems) as well as for research design and the interpretation of group average data.     

Temporal associations between morningness/eveningness,problematic social media use,psychological distress and daytime sleepiness: Mediated roles of sleep quality and insomnia among young adults

The extant literature has suggested relationships between an individual's chronotype (in relation to morningness/eveningness) and several outcomes, including addictive disorders, psychological distress and daytime sleepiness. Moreover, sleep quality has been proposed to be a mediator in the aforementioned relationships. Consequently, the aim of the present study was to investigate the complex relationship between morningness/eveningness, problematic social media use, psychological distress and daytime sleepiness, with the potential mediators of sleep quality and insomnia. All participants (N = 1,791 [30.1% males]; mean age = 27.2 years, SD = 10.1) completed a battery of psychometric scales, including a reduced version of the Morningness‐Eveningness Questionnaire (at baseline), the Pittsburgh Sleep Quality Index and Insomnia Severity Index (1 month after baseline assessment), the Bergen Social Media Addiction Scale, the Hospital Anxiety and Depression Scale, and the Epworth Sleepiness Scale (2 months after baseline assessment). The impacts of morningness‐eveningness on problematic social media use, anxiety, depression and daytime sleepiness were found in the mediation models. Furthermore, the mediated effects of insomnia and sleep quality were observed. The present study's results emphasize the importance of promoting healthy sleep habits and sleep hygiene behaviours, and that of early detection of sleep problems among individuals who have the eveningness chronotype, because this would significantly improve their health outcomes.     

Subjective sleepiness and accident risk avoiding the ecological fallacy

The present study of sleepiness and accident risk in a HI-FI car simulator aimed to provide subject-level relative risks (RR) with 95% confidence intervals (CI) for different levels of subjective sleepiness measured with the Karolinska Sleepiness Scale (KSS), 1 = very alert, 9 = very sleepy, fighting sleep, an effort to staying awake. Five male and five female shift workers, mean age 37 years, participated with a 2-h drive (08:00-10:00 hours) in a dynamic high-fidelity moving base driving simulator, after a night of work and after a night of sleep. Subjective sleepiness was measured with KSS every 5 min and events of incidents (two wheels outside the right lane), accidents (two wheels off the road or four wheels in opposite lane) and crashes (four wheels off the road) were recorded. The probability of an accident was modelled with a Generalized Linear Mixed Model approach to estimate subject-specific effects, rather than group average effects, to avoid the ecological fallacy. The results showed that sleepiness was strongly related to accident risk. An average subject was estimated at 28.2 times (95% CI RR = 10.7-74.1) increased risk at KSS = 8 and at 185 times (95% CI RR = 42-316) at KSS = 9 compared with KSS = 5. There were large individual differences in event propensity that complicates the prediction of absolute accident risk for individual subjects.