Implementation of the Danish return-to-work program: process evaluation of a trial in 21 Danish municipalities.

OBJECTIVES: The aim of this study was to evaluate the implementation of the Danish national return-to-work (RTW) program in 21 Danish municipalities. METHODS: We conducted a structured process evaluation on (i) reach and recruitment, (ii) fidelity, (iii) dose-delivered, (iv) dose-received, and (v) context by formulating 29 implementation criteria and analyzing qualitative and quantitative data from administrative records, interviews, field notes, and questionnaires. RESULTS: All municipalities integrated the basic features of the RTW program into the existing framework of the sickness benefit management system to an acceptable degree, ie, establishment of RTW teams, participation of RTW team members in the training courses, and following the general procedures of the program. However, the level of implementation varied considerably between the municipalities, particularly with respect to fidelity (defined as implementation consistent with the principles of the interdisciplinary RTW process). Five municipalities had high and eight had low fidelity scores. Similar large differences were found with regard to dose-delivered, particularly in the quality of cooperation with beneficiaries, employers, and general practitioners. Only 50% of the first consultations with the RTW coordinator were conducted in time. Among participants who were employed when their sickness absence period started, only 9% had at least one meeting with their workplace. CONCLUSION: It was feasible to implement the basic features of the Danish RTW program, however, large variations existed between municipalities. Establishment of well-functioning interdisciplinary RTW teams might require more time and resources, while ensuring early assessment and more frequent cooperation with employers might need more general adjustments in the Danish sickness benefit system.

A multisite randomized controlled trial on time to self-support among sickness absence beneficiaries. The Danish national return-to-work programme.

BACKGROUND: In 2010, the Danish Government launched the Danish national return-to-work (RTW) programme to reduce sickness absence and promote labour market attainment. Multidisciplinary teams delivered the RTW programme, which comprised a coordinated, tailored and multidisciplinary effort (CTM) for sickness absence beneficiaries at high risk for exclusion from the labour market. The aim of this article was to evaluate the effectiveness of the RTW programme on self-support. METHODS: Beneficiaries from three municipalities (denoted M1, M2 and M3) participated in a randomized controlled trial. We randomly assigned beneficiaries to CTM (M1: n = 598; M2: n = 459; M3: n = 331) or to ordinary sickness absence management (OSM) (M1: n = 393; M2: n = 324; M3: n = 95). We used the Cox proportional hazards model to estimate hazard ratios (HR) comparing rates of becoming self-supporting between beneficiaries receiving CTM and OSM. RESULTS: In M2, beneficiaries from employment receiving CTM became self-supporting faster compared with beneficiaries receiving OSM (HR = 1.32, 95% CI: 1.08-1.61). In M3, beneficiaries receiving CTM became self-supporting slower than beneficiaries receiving OSM (HR = 0.72, 95% CI: 0.54-0.95). In M1, we found no difference between the two groups (HR = 0.99, 95% CI: 0.84-1.17). CONCLUSION: The effect of the CTM programme on return to self-support differed substantially across the three participating municipalities. Thus, generalizing the study results to other Danish municipalities is not warranted. TRIAL REGISTRATION: ISRCTN43004323.

Month-to-month variation in sleep among healthy, Scandinavian daytime workers.

BACKGROUND: The overall purpose of the present study was to attain more insight in month-to-month variation of sleep duration and quality in order to improve design and interpretation of, e.g. epidemiological studies using sleep as outcome. METHODS: The study design entailed monthly self-reports from 38 (26 women/12 men) daytime workers, who completed the Karolinska Sleep Diary (KSD) once a month during one year. A subgroup (n = 16) also wore actigraphs on one day every month during a year. Self-reports of bedtime, time of awakening, sleep duration, individual sleep characteristics, disturbed sleep index (DSI, 4 items) and awakening index (AWI, 3 items) were analyzed together with actigraphy-derived measures. Hours of daylight were used to test for circa-annual variation in statistical models adjusted for intake of hypnotics and alcohol, gender, age and within-person variability. RESULTS: Hours of daylight were found to be associated to self-reported bedtime (p = 0.032) and DSI (p = 0.030), thereby indicating a circa-annual variation. Bedtime was delayed by 1.8 min (95% CI: 0.6-2.9 min) per 1 hour increase in length of daylight. Sleep was slightly more disturbed during the winter. CONCLUSION: Only circa-annual variation in self-reports of bedtime and DSI were observed in a healthy daytime working population, and the effects were small. Therefore potential bias due to circa-annuality in the studied parameters appears to be of limited concern in adult daytime working populations.

Effect of the Danish return-to-work program on long-term sickness absence: results from a randomized controlled trial in three municipalities.

OBJECTIVES: The aim of this study was to evaluate the effect of the Danish return-to-work (RTW) program on long-term sickness absence in a randomized controlled trial in three municipalities. METHODS: The intervention group comprised 1948 participants while the control group comprised 1157 participant receiving ordinary sickness benefit management (OSM). Study participants were working-age adults receiving long-term (≥8 weeks or more) benefits, included regardless of reason for sickness absence or employment status. Each beneficiary was followed-up for a maximum period of 52 weeks. Cox proportional hazards model was used to estimate hazard ratios (HR) for return to work (RTW) with 95% confidence intervals (95% CI). RESULTS: The intervention effect differed significantly between the municipalities (P=0.00005). In one municipality (M2) the intervention resulted in a statistically significant increased rate of recovery from long-term sickness absence (HR 1.51, 95% CI 1.31-1.74). In the other two municipalities, the intervention did not show a statistically significant effect (HR M11.12, 95% CI 0.97-1.29, and HR M30.80, 95% CI 0.63-1.03, respectively). Adjustment for a series of possible confounders only marginally altered the estimated HR. CONCLUSION: The effect of the intervention differed substantially between the three municipalities, indicating that that contextual factors are of major importance for success or failure of this complex intervention.

Distribution of subjective health complaints, and their association with register based sickness absence in the Danish working population.

AIMS: To describe the distribution of subjective health complaints (SHCs) in a Danish working population and the associations between SHC and register based sickness absence. METHODS: The study entailed 2876 men and 3574 women aged 18-59 years that constituted the 2005 panel in the Danish Work Environment Cohort Study (DWECS). All had completed a subjective health complaints inventory and the Nordic Musculoskeletal Questionnaire (NMQ). Seven SHC/NMQ indices were constructed and merged with subsequently collected data on prolonged sickness absence periods (each period > 14 days) that was registered in the national Danish register on social transfer payments: the DREAM register. Ordinal logistic regression was used to model the cumulative odds for sickness absence as a function of strata. RESULTS: The majority of participants reported at least one SHC during a 30-day period (circa 89% of the men and 95% of the women). The reports of severe SHC, defined as recurring SHC within the 30-day period, were less common. About 55% of the men and 68% of the women reported at least one severe SHC during a 30-day period. The odds ratios of sickness absence increased with the number of SHC a participant acknowledged. The odds ratios were slightly reduced after adjusting for age, disease history and social class. CONCLUSIONS: The majority of the working population in Denmark report at least one SHC during a 30-day period. Roughly half of the population report having at least one recurrent (often to very often) SHC during the last 30-days (severe SHC). Reporting the presence of several SHCs increases the likelihood of having more prospectively registered periods of sickness absence above two weeks.

The Danish national return-to-work program--aims, content, and design of the process and effect evaluation.

The Danish national return-to-work (RTW) program aims to improve the management of municipal sickness benefit in Denmark. A study is currently ongoing to evaluate the RTW program. The purpose of this article is to describe the study protocol. The program includes 21 municipalities encompassing approximately 19 500 working-age adults on long-term sickness absence, regardless of reason for sickness absence or employment status. It consists of three core elements: (i) establishment of multidisciplinary RTW teams, (ii) introduction of standardized workability assessments and sickness absence management procedures, and (iii) a comprehensive training course for the RTW teams. The effect evaluation is based on a parallel group randomized trial and a stratified cluster controlled trial and focuses on register-based primary outcomes - duration of sickness absence and RTW - and questionnaire-based secondary outcomes such as health and workability. The process evaluation utilizes questionnaires, interviews, and municipal data. The effect evaluation tests whether participants in the intervention have a (i) shorter duration of full-time sickness absence, (ii) longer time until recurrent long-term sickness absence, (iii) faster full RTW, (iv) more positive development in health, workability, pain, and sleep; it also tests whether the program is cost-effective. The process evaluation investigates: (i) whether the expected target population is reached; (ii) if the program is implemented as intended; (iii) how the beneficiaries, the RTW teams, and the external stakeholders experience the program; and (iv) whether contextual factors influenced the implementation. The program has the potential to contribute markedly to lowering human and economic costs and increasing labor force supply. First results will be available in 2013. The trial registrations are ISRCTN43004323, and ISRCTN51445682.

Cortisol, sleep, and recovery - Some gender differences but no straight associations.

BACKGROUND: Work related fatigue has been suggested as a link in the assumed sequence of events between repeated adverse work demands and the development of work related stress, which may be associated with changes in concentrations of cortisol, psychological overload and, in the long run, health problems. Insufficient sleep is a contributing factor to lack of recovery, but previous studies on associations between subjective aspects of sleep and recovery, and cortisol, have been inconclusive. The aim with the present study was to examine possible associations between cortisol measures and (I) self-rated recovery, (II) occupational fatigue and (III) subjective sleep quality the night preceding cortisol sampling. Further, possible gender differences were tested. METHODS: Salivary cortisol was measured in 581 persons during a working day, at awakening, +30 min and in the evening. Various measures of subjective sleep and recovery were analyzed in relation to cortisol. RESULTS: Few correlations between cortisol and any sleep- or recovery parameters were found. However, some significant associations were found between cortisol and a few measures of more chronic aspects of sleep and recovery. Gender stratified analyses showed somewhat differing associations among men and women. This indicates that possible associations and pathways between lack of recovery/sleepiness and cortisol, and in the long run, unhealth, may not be similar for men and women.

Can the job content questionnaire be used to assess structural and organizational properties of the work environment?

OBJECTIVE: The theory behind the Job Content Questionnaire (JCQ) presumes that the "objective" social environment is measurable via self-report inventories such as the JCQ. Hence, it is expected that workers in identical work will respond highly similar. However, since no studies have evaluated this basic assumption, we decided to investigate whether workers performing highly similar work also responded similarly to the JCQ. METHODS: JCQ data from a rubber-manufacturing (RM: n = 95) and a mechanical assembly company (MA: n = 119) were examined. On each worksite, men and women performed identical machine-paced job tasks. A population sample (n = 8,542) served as a reference group. RESULTS: In both the RM and MA groups, the job support questions were rated most similar. Yet, there was a substantial variation as regards choosing to agree or disagree with single JCQ items. The variation was also reflected in the scale scores. In the RM and MA groups, the variance of job demand and job control scores was 64-87% of that of the population sample. For job support scores, the corresponding variation was 42-87%. CONCLUSION: Conducting highly similar work does not lead to highly similar reports in the JCQ. In view of the large response variation, it seems that the attempt to avoid personal influence by minimizing the self-reflexive component in the questions asked, and using response alternative that indicates degree of agreement, does not seem to work as intended.

Low heart rate variability is associated with extended pain-related sick leave among employed care-seekers.

OBJECTIVE: To examine the association between autonomic regulation and length of pain-related sick leave in subjects receiving a cognitive behavioural therapy-based return to work intervention. METHODS: Sixty-five persons (29 men, 36 women) on pain-related sick leave participated in the study. Electrocardiograms were recorded in the clinic during supine rest, passive head-up tilt, standing, and seated rest, and in the home during seated rest and sleep. Spectral components of heart rate variability were derived from short-term (5 min) segments of electrocardiogram recordings. The number of days on sick leave was obtained from register data for 3 months before to 6 months after seeking care at the primary healthcare clinic. RESULTS: Extended sick leave (> 121 days) compared with short sick leave (< 29 days) was associated with higher heart rate, and lower heart rate variability in supine rest and the seated position. The associations in supine rest were marginally weakened by adjusting for offensive behaviours at work. (for example, exposure to bullying, sexual harassment, unpleasant teasing, etc.) CONCLUSION: Higher heart rate and lower heart rate variability measured in the awake resting condition predicts extended sick leave in care-seeking individuals. Further research is needed to clarify the underlying nature and causal role of altered autonomic regulation with regard to extended pain-related sick leave.

Cortisol variability and self-reports in the measurement of work-related stress.

We examined whether a high cortisol awakening response (CAR) and low cortisol decline over the day (CDD) are related to self-reported work stress and well-being, and whether there are gender differences in these relationships. Three hundred eighty-three working men and women responded to a survey measuring job stress factors, mastery at work, symptoms and well-being. Salivary cortisol was sampled at awakening, after 45 min and at 21:00, from which the variables CAR and CDD were defined. A high CAR was associated with lower perceived job control and work mastery, and poorer well-being. Low CDD was associated only with higher job demands, but the self-report scores showed a number of interactions between cortisol group and gender. Among women, those showing a low CDD, compared with those with a higher CDD, had more favourable scores on a number of job stress factors and symptom load. In contrast, among men, a similar comparison showed those with low CDD to have poorer scores on job stress factors and symptom load. We conclude that individuals displaying high CAR or low CDD differ from those not displaying these cortisol profiles in self-report of work stress and well-being, and that gender differences appear in these relationships.

Heart rate variability changes in physicians working on night call.

PURPOSE: Adverse effects by night-call duty have become an important occupational health issue. The aim of this study was to investigate whether the heart rate variability (HRV) differed during recovery from day work and night-call duty between distinct physician specialities. METHODS: We studied the impact of a 16-h night-call duty on autonomic balance, measured by HRV, among two physician groups differing with respect to having to deal with life-threatening conditions while on call. Nineteen anaesthesiologists (ANEST) and 16 paediatricians and ear, nose and throat surgeons (PENT) were monitored by ambulatory digital Holter electrocardiogram (ECG). Heart rate variability was analysed between 21:00 and 22:00 after an ordinary workday, on night call and in the evening post-call. Absolute and normalized high-frequency power (HF, HFnu) were the main outcome variables, expressing parasympathetic influence on the heart. RESULTS: ANEST had lower HF power than PENT while on night call and post-daytime work (p < 0.05), but not at post-night call. In the whole group of physicians, HFnu was lower on call and post-daytime work compared with post-night-call duty (p < 0.05). CONCLUSIONS: The physiological recovery after night duty seemed sufficient in terms of HRV patterns for HFnu, reflecting autonomic balance and did not differ between specialities. However, the less dynamic HRV after daytime work and during night-call duty in the ANEST group may indicate a higher physiological stress level. These results may contribute to the improvement of night-call schedules within the health care sector.

Seasonal variation in self-reported arousal and subjective health complaints.

Many aspects of human physiology and behavior are seasonally related. Although there are many studies using self-ratings of, for example, subjective health and stress, few involve adjusting effects for seasonal differences. To estimate the need of adjusting for season in field studies, 24 healthy men and women were studied in a design that required them to fill in questionnaires on one workday every month, for 12 consecutive months. The results showed that ratings of stress were higher during winter and early spring, but only in the early afternoon and not in the morning or the evening. While some subjective health complaints were rated higher during winter, the ratings of energy and self-rated health did not vary throughout seasons. This concludes that seasonal variations may be a source of bias in questionnaire studies. Yet, further studies are needed to more definitely sort out which phenomena and self-rating measures that co-vary with season.

Sleep and recovery in physicians on night call: a longitudinal field study.

BACKGROUND: It is well known that physicians' night-call duty may cause impaired performance and adverse effects on subjective health, but there is limited knowledge about effects on sleep duration and recovery time. In recent years occupational stress and impaired well-being among anaesthesiologists have been frequently reported for in the scientific literature. Given their main focus on handling patients with life-threatening conditions, when on call, one might expect sleep and recovery to be negatively affected by work, especially in this specialist group. The aim of the present study was to examine whether a 16-hour night-call schedule allowed for sufficient recovery in anaesthesiologists compared with other physician specialists handling less life-threatening conditions, when on call. METHODS: Sleep, monitored by actigraphy and Karolinska Sleep Diary/Sleepiness Scale on one night after daytime work, one night call, the following first and second nights post-call, and a Saturday night, was compared between 15 anaesthesiologists and 17 paediatricians and ear, nose, and throat surgeons. RESULTS: Recovery patterns over the days after night call did not differ between groups, but between days. Mean night sleep for all physicians was 3 hours when on call, 7 h both nights post-call and Saturday, and 6 h after daytime work (p < 0.001). Scores for mental fatigue and feeling well rested were poorer post-call, but returned to Sunday morning levels after two nights' sleep. CONCLUSIONS: Despite considerable sleep loss during work on night call, and unexpectedly short sleep after ordinary day work, the physicians' self-reports indicate full recovery after two nights' sleep. We conclude that these 16-hour night duties were compatible with a short-term recovery in both physician groups, but the limited sleep duration in general still implies a long-term health concern. These results may contribute to the establishment of safe working hours for night-call duty in physicians and other health-care workers.

Delayed manifestations of CNS effects in formerly exposed printers--a 20-year follow-up.

Whether long-term occupational exposure to organic solvents may affect mental and cognitive functioning later in life, remains unclear. In this study, twelve rotogravure printers formerly exposed to toluene and 19 referents, all initially examined in the mid-1980s, were reexamined after twenty years, applying neuropsychological tests, symptoms and social interaction questionnaires, medical examination, and exposure assessment of each individual's cumulative exposure. By far the most extensive exposure, mainly toluene, had occurred before 1985. The printers were found to have deteriorated more than their referents in cognitive functioning affecting reasoning and associative learning. No relevant additional exposure during the lengthy time period between assessments could explain this discrepancy. In addition, printers performed significantly worse than the referents in verbal memory and sustained attention at follow-up, where also a dose-effect relationship was noted for reasoning. While the printers did not report more subjective cognitive complaints than the referents, a slightly higher depression score was noted for the printers. The findings of significantly worse deteriorations in cognitive functioning in previously toluene-exposed printers are in line with our hypothesis that sub-clinical deficits during the working life may become manifest later in life, indicating that exposure may in fact interact with ageing. However, considering the small study groups the results must be interpreted with caution.

Effects on sleep-related problems and self-reported health after a change of shift schedule.

This study prospectively examined the effects of a change of shift schedule from a fast forward-rotating schedule to a slowly backward-rotating one. The initial schedule had a forward rotation from mornings to afternoons to nights over 6 consecutive days, with 2 days on each shift followed by 4 days off before the next iteration of the cycle, whereas the new schedule had a slower backward rotation from mornings to nights to afternoons, with 3 days on a given shift followed by 3 days off before the next shift. Shift workers (n = 118) were compared with a reference group of daytime workers (n = 67) from the same manufacturing plant by means of questionnaires covering subjective health, sleep and fatigue, recovery ability, satisfaction with work hours, work-family interface, and job demands, control, and support. Data were collected 6 months before implementing the new schedule and at a follow-up 15 months later. As predicted, on most dimensions measured the shift workers displayed clear improvements from initially poorer scores than daytime workers, and the daytime workers displayed no improvements.

Physiological and psychological reactions to work in men and women with identical job tasks.

Differences in physiological functioning in the hypothalamus-pituitary-adrenal cortex axis and the autonomic nervous system have been suggested to contribute to many of the health differences that may be observed between men and women as well as being relevant for the development of musculoskeletal pain. To clarify whether men and women with identical work tasks reacted differently when doing work known to induce musculoskeletal pain, ratings and physiological measurements were obtained at work start (15:30) and at the end of the workshift (22:30) on 17 men and 20 women. Men showed a larger decrease in perceived energy levels during the workshift but there were no differences between men and women as regards cortisol, adrenaline, noradrenaline, heart-rate activation, perceived stress, pain and physical exertion. In conclusion, differential physiological activation during the workshift seem to be an unlikely mechanism for explaining gender differences in pain associated with exposure to awkward and repetitive movements.

Seasonal variation in human salivary cortisol concentration.

Measurement of cortisol concentration can contribute important information about an individual's ability to adjust to various environmental demands of both physical and psychosocial origin. However, one uncertainty that affects the possibilities of correctly interpreting and designing field studies is the lack of observations of the impact of seasonal changes on cortisol excretion. For this reason, the month-to-month changes in diurnal cortisol concentration, the awakening cortisol response (ACR), maximum morning concentration, and fall during the day were studied in a group of 24 healthy men and women 32 to 61 yrs of age engaged in active work. On one workday for 12 consecutive months, participants collected saliva at four time points for determination of cortisol: at awakening, +30 min, +8 h, and at 21:00 h. Data were analyzed by a repeated measures design with month (12 levels) and time-of-day (4 levels) as categorical predictors. Cortisol concentrations were analyzed on a log scale. The diurnal pattern of cortisol was similar across months (interaction between month and time of day: p>0.4). The main effects of month and time-of-day were statistically significant (p<0.001). Highest concentrations were observed in February, March, and April, and lowest concentrations were observed in July and August. There were no statistically significant effects in any of the other measures, or between men and women. In conclusion, a seasonal variation in salivary cortisol concentrations was detected in an occupationally active population. Thus, seasonal variation needs to be taken into account when designing and evaluating field studies and interventions and when making comparisons across studies.

A two-week monitoring of self-reported arousal, worry and attribution among persons with annoyance attributed to electrical equipment and smells.

Non-patients attributing annoyance to either smells (smell annoyed; SA, n= 29) or electrical equipment (electrically annoyed; EA, n= 17), or both (generally annoyed; GA, n= 38), were monitored for 2 weeks through daily self-ratings of arousal (stress), sleep disturbances, health complaints, worry about hypersensitivity reactions, avoidance behaviors, and attributions of health complaints to electrical equipment and smells. In parallel, a demographically matched reference group was followed (n= 56). GA persons reported higher arousal (stress), more subjective health complaints, and more sleep disturbances than the other groups. About 60% in the GA and EA groups reported intentional avoidance behavior, compared to 31% in the SA group and 2% of the referents. Worry and attribution to environmental factors was also more frequent among GA persons than in the other groups. Thus, even at sub-clinical levels, environmental annoyance generalized to several triggers seems to be associated with behaviors commonly observed among patients with idiopathic environmental intolerance.

High cost-benefit of early team-based biomedical and cognitive-behaviour intervention for long-term pain-related sickness absence.

OBJECTIVE: To report the results from a prospective, cognitive-behavioural team-based, individually geared, low-intensity, rehabilitation programme, randomly assigned to care-seekers in primary care physiotherapy with new pain-related sick leave, and to examine a possible reduction in social security expenditure. METHODS: A total of 194 care-seekers were included in a stepwise procedure from November 2000 to February 2002. Control group n = 381. RESULTS: The median number of days of sick leave in the intervention group was 22 during the first 6-month period. After 180 days 5.2% were still on sick leave and after 360 days 4.2%. The comparable figures in the control group were 30 days, 9.7% and 7.2%, respectively. Reductions in social security expenditure were statistically significant from the fourth month. As predicted, clinically relevant subgroups contributed differently to this reduction, both early and later on. The overall problem for one-third of the subgroups was insufficient co-ordination from the employer and the social security executive. CONCLUSION: It was possible to reduce the social security expenditure in this setting. The intervention costs were balanced out during the first year. A large potential for further cost reductions was identified in increased implementation of workplace-based return-to-work interventions.

Concentrations of cortisol, testosterone and glycosylated haemoglobin (HbA1c) among construction workers with 12-h workdays and extended workweeks.

OBJECTIVES: Working on large scale construction sites have been shown to have severe health consequences in terms of increased risk of hospitalization and disability retirement compared to construction work in general. The aim of the present study was to investigate whether large scale construction work involving 12-h workdays and extended workweeks leads to insufficient recovery measured as increased catabolic and decreased anabolic metabolism. METHODS: The study group comprised 40 male construction workers of which 21 had 12-h workdays and extended workweeks (56 h/workweek). The comparison group consisted of 19 male construction workers, who worked regular hours (37 h/week, weekends off). Measurements of concentrations of cortisol in saliva and free testosterone and glycosylated haemoglobin (HbA(1c)) in blood were made in a repeated measures design during 2 workweeks for both groups supplemented with 1 week off for construction workers with extended workweeks. RESULTS: The diurnal profile of concentrations of salivary cortisol for construction workers with extended workweeks differed from the diurnal profile of salivary cortisol for those with regular work schedules (P < 0.001). The construction workers with extended workweeks tended to have 15% [95% CI -3%; 37%] higher concentrations of free testosterone in serum compared to construction workers with regular work schedules (P = 0.09). There were no differences between the two groups with respect to concentrations of HbA(1c). There was no increasing trend in concentrations of cortisol or decreasing trend in concentrations of testosterone during the extended workweek. The diurnal profile for concentrations of cortisol differed between workdays and days off for construction workers with extended workweeks (P = 0.003). CONCLUSION: In conclusion, we observed no indications of insufficient recovery in terms of increased catabolic or decreased anabolic metabolism in construction workers with 12-h workdays and extended workweeks compared to construction workers with regular work schedules.