Lee Di Milia

Circadian typology: a comprehensive review.

The interest in the systematic study of the circadian typology (CT) is relatively recent and has developed rapidly in the two last decades. All the existing data suggest that this individual difference affects our biological and psychological functioning, not only in health, but also in disease. In the present study, we review the current literature concerning the psychometric properties and validity of CT measures as well as individual, environmental and genetic factors that influence the CT. We present a brief overview of the biological markers that are used to define differences between CT groups (sleep–wake cycle, body temperature, cortisol and melatonin), and we assess the implications for CT and adjustment to shiftwork and jet lag. We also review the differences between CT in terms of cognitive abilities, personality traits and the incidence of psychiatric disorders. When necessary, we have emphasized the methodological limitations that exist today and suggested some future avenues of work in order to overcome these. This is a new field of interest to professionals in many different areas (research, labor, academic and clinical), and this review provides a state of the art discussion to allow professionals to integrate chronobiological aspects of human behavior into their daily practice.

Sleep disorders, medical conditions, and road accident risk.

Sleep disorders and various common acute and chronic medical conditions directly or indirectly affect the quality and quantity of ones sleep or otherwise cause excessive daytime fatigue. This article reviews the potential contribution of several prevalent medical conditions - allergic rhinitis, asthma, chronic obstructive pulmonary disease, rheumatoid arthritis/osteoarthritis - and chronic fatigue syndrome and clinical sleep disorders - insomnia, obstructive sleep apnea, narcolepsy, periodic limb movement of sleep, and restless legs syndrome - to the risk for drowsy-driving road crashes. It also explores the literature on the cost-benefit of preventive interventions, using obstructive sleep apnea as an example. Although numerous investigations have addressed the impact of sleep and medical disorders on quality of life, few have specifically addressed their potential deleterious effect on driving performance and road incidents. Moreover, since past studies have focused on the survivors of driver crashes, they may be biased. Representative population-based prospective multidisciplinary studies are urgently required to clarify the role of the fatigue associated with common ailments and medications on traffic crash risk of both commercial and non-commercial drivers and to comprehensively assess the cost-effectiveness of intervention strategies.

Reviewing the Psychometric Properties of Contemporary Circadian Typology Measures

The accurate measurement of circadian typology (CT) is critical because the construct has implications for a number of health disorders. In this review, we focus on the evidence to support the reliability and validity of the more commonly used CT scales: the Morningness-Eveningness Questionnaire (MEQ), reduced Morningness-Eveningness Questionnaire (rMEQ), the Composite Scale of Morningness (CSM), and the Preferences Scale (PS). In addition, we also consider the Munich ChronoType Questionnaire (MCTQ). In terms of reliability, the MEQ, CSM, and PS consistently report high levels of reliability (>0.80), whereas the reliability of the rMEQ is satisfactory. The stability of these scales is sound at follow-up periods up to 13 mos. The MCTQ is not a scale; therefore, its reliability cannot be assessed. Although it is possible to determine the stability of the MCTQ, these data are yet to be reported. Validity must be given equal weight in assessing the measurement properties of CT instruments. Most commonly reported is convergent and construct validity. The MEQ, rMEQ, and CSM are highly correlated and this is to be expected, given that these scales share common items. The level of agreement between the MCTQ and the MEQ is satisfactory, but the correlation between these two constructs decreases in line with the number of “corrections” applied to the MCTQ. The interesting question is whether CT is best represented by a psychological preference for behavior or by using a biomarker such as sleep midpoint. Good-quality subjective and objective data suggest adequate construct validity for each of the CT instruments, but a major limitation of this literature is studies that assess the predictive validity of these instruments. We make a number of recommendations with the aim of advancing science. Future studies need to (1) focus on collecting data from representative samples that consider a number of environmental factors; (2) employ longitudinal designs to allow the predictive validity of CT measures to be assessed and preferably make use of objective data; (3) employ contemporary statistical approaches, including structural equation modeling and item-response models; and (4) provide better information concerning sample selection and a rationale for choosing cutoff points.

Demographic factors, fatigue, and driving accidents: An examination of the published literature.

This article reviews the literature pertaining to the association between demographic variables (e.g., age, sex, race, socio-economic status) with fatigue, and when feasible, accident risk. It also explores their potential influence and interaction with some working arrangements, commute time, personality characteristics, and circadian chronotype. Fatigue has been implicated in a range of impairments that can have detrimental effects on individuals, and it is differentially associated with conventional demographic variables. However, several major methodological limitations prevent clear conclusions. First, there is absence of a shared definition both within and across disciplines. Second, although fatigue has been investigated using a variety of diverse designs, they have either been too weak to substantiate causality or lacked ecological validity. Third, while both subjective and objective measures have been used as dependent variables, fatigue has been more often found to be more strongly linked with the former. Fourth, with the exception of age and sex, the influence of other demographic variables is unknown, since they have not yet been concomitantly assessed. In instances when they have been assessed and included in statistical analyses, they are considered as covariates or confounders; thus, their contribution to the outcome variable is controlled for, rather than being a planned aspect of investigation. Because the interaction of demographic factors with fatigue is largely a neglected area of study, we recommend greater interdisciplinary collaborations, incorporation of multiple demographic variables as independent factors, and use of within-participant analyses. These recommendations would provide meaningful results that may be used to inform public policy and preventive strategies.

Aging and shift work: a complex problem to face.

The baby boomer generation is well into the 50+ age bracket, making it one of the largest demographic age cohorts. Whereas this cohort would have previously considered retirement, the evidence suggests that it will remain in the workforce for a longer period in response to a number of social and economic drivers. Mandatory retirement has either been abolished or is under consideration. An increased and healthier life expectancy means that people may work longer for financial and/or psychological reasons. In addition, a global shortage of skilled labor will result in efforts to keep employees in the workplace for longer periods. These trends have a number of implications for working time. What are the health implications of an aging workforce? How do we sustain good work ability into the latter years? What do we know about aging and shift work? What actions are required in the workplace to assist aging workers? This paper is not a comprehensive review of the literature but serves to highlight the complexities in understanding the relationship between shift work and aging. We discuss aging and human function and, in particular, the impact of aging on the circadian system. In addition, we outline new policy directions in this area and raise several suggestions to assist the well‐being of aging workers.

What aspects of shiftwork influence off-shift well-being of healthcare workers?

Characteristics of shiftwork schedules have implications for off-shift well-being. We examined the extent to which several shift characteristics (e.g., shift length, working sundays) are associated with three aspects of off-shift well-being: work-to-family conflict, physical well-being, and mental well-being. We also investigated whether these relationships differed in four nations. The Survey of Work and Time was completed by 906 healthcare professionals located in Australia, Brazil, Croatia, and the USA. Hierarchical multiple regression analyses supported the hypothesis that shiftwork characteristics account for significant unique variance in all three measures of well-being beyond that accounted for by work and family demands and personal characteristics. The patterns of regression weights indicated that particular shiftwork characteristics have differential relevance to indices of work-to-family conflict, physical well-being, and mental well-being. Our findings suggest that healthcare organizations should carefully consider the implications of shiftwork characteristics for off-shift well-being. Furthermore, although our findings did not indicate national differences in the nature of relationships between shift characteristics and well-being, shiftwork characteristics and demographics for healthcare professionals differ in systematic ways among nations; as such, effective solutions may be context-specific.

Shift Work Disorder in a Random Population Sample – Prevalence and Comorbidities

Few studies have investigated the presence of shift work disorder (SWD) in the general community. We addressed many of the limitations in this literature and present new findings. SWD has been treated as an ‘all or none’ construct but we propose the need to consider the ‘severity’ of the disorder. Using random digit dialling, we randomly recruited 1163 participants. Participants completed an extensive battery of scales and questions concerning work, health and individual differences. Three questions based on the criteria from the International Classification for Sleep Disorders were used to categorise participants with SWD (n = 176). In addition, we asked participants whether SWD interfered with aspects of their life and high ratings were used to define severe shift work disorder (SSWD). The prevalence of SWD was 32.1% among night workers and 10.1% in day workers (p<.001). SSWD was present in 9.1% of night workers and 1.3% of day workers (p<.001). Adjusted logistic regression analyses found significant associations between SWD and night work (OR  = 3.35, CI 2.19-5.12), weekly work hours (OR  = 1.02, CI 1.00–1.04), short sleep (≤6 h; OR  = 2.93, CI 1.94–4.41), languidity (OR  = 1.11, CI 1.06–1.16) and resilience (OR  = 0.56, CI 0.43–0.81). Night work, short sleep, languidity, and hypertension were significantly associated with SSWD. Overall, participants with SSWD slept 0.80 h less than other participants (p<.001). Night work, short sleep and languidity were associated with both SWD and SSWD. Day workers with SWD symptoms reported significantly shorter sleep duration, higher levels of languidity and worked longer working hours compared to day workers without SWD.

The association between short sleep and obesity after controlling for demographic, lifestyle, work and health related factors

OBJECTIVE The relationship between short sleep and obesity remains unclear, and a possible explanation is that many studies have not included sufficient control variables in the analyses. We examined the association between sleep and being overweight or obese after adjusting for the confounding contributions of 17 variables. METHODS A random sample of 1162 Australian adults from three regional cities in central Queensland, Australia, participated in a telephone survey. A series of increasingly complex multinomial logistic regression models were employed to assess the association between short sleep (< or = 6 h) being overweight (body mass index [BMI] 25-29.99 kg/m2) and obesity (BMI, > or = 30 kg/m2), while controlling for several demographic, lifestyle, work, and health-related variables. RESULTS The results suggested obesity was significantly associated with short sleep, age, male gender, lower education level, less physical activity, more sitting time, working longer hours, drinking more alcohol, having diabetes mellitus (DM), and having hypertension. Being overweight was significantly associated with age, male gender, smoking, and working more than 43hours per week. CONCLUSIONS After adjustment of several confounding variables, a significant association between short sleep and obesity was obtained, but there was no association between short sleep and being overweight. Additional studies applying comprehensive analytic models and stronger research designs are needed to confirm our findings.

Supervisor behaviours that facilitate training transfer

Purpose – The purpose of this paper is to describe the supervisor behaviours that employees found to be helpful and unhelpful in facilitating training transfer. The study aims to provide rich qualitative data from the employees perspective.Design/methodology/approach – This study utilises a cross‐sectional design. A case study and a qualitative interpretivist approach were used to interpret the employees responses. In total 24 semi‐structured interviews were conducted and responses were analysed with the aid of NVivo.Findings – The results suggested what supervisors did prior to, during and after course attendance was critical to training transfer. Supportive behaviours prior to the course included motivating, encouraging and setting expectations. Practical support provided during the course signalled the value that the supervisor placed on the course. Meetings held after the course provided the best opportunity to support transfer. Transfer was maximised when participants experienced a positive role mo...

Morningness or Morning Affect? A Short Composite Scale of Morningness

The Composite Scale of Morningness (CSM) is a widely used measure of behavioral temporal preference, and it is highly reliable across cultures. There are several competing models concerning its factor structure. We used confirmatory factor analysis (CFA) to replicate the two‐and three‐factor models, and, in addition, we examined the utility of the four‐item morning affect scale as a proxy for the full CSM. We tested these models in a large student sample (N=1396). The chi‐square result for the two‐ and three‐factor models indicated they did not adequately fit the data, and the modification indices suggested some items could be correlated. Allowing these items to correlate failed to produce a non‐significant chi‐square result, but some improvements to the incremental fit indices and root mean square error of approximation (RMSEA) were found. In particular, the three‐factor model seemed satisfactory. CFA of the morning‐affect scale also failed to fit the data, but the incremental fit indices and RMSEA were strong. For each of these three models, there was no significant difference between the invariant (no sex difference) and variant (sex difference) models. However, in each model, a critical ratio difference was found on the standardized regression weights between males and females on item 12. The morning‐affect scale had high reliability (0.83) and demonstrated satisfactory construct validity against the preferences scale and time to sleep and wake. In addition, high and low morning‐affect groups reported significant sleepiness differences by time of day. These results suggest the morning‐affect scale may be a useful proxy for the full scale. Furthermore, the items make no reference to time‐of‐day and may better facilitate cross‐cultural research. Studies using population‐based samples are recommended to further test the efficacy of the morning‐affect scale.