9.0 SleepWatch ® ( Actigraphy) Measure of Sleep on Workdays and Non-Workdays
It was hypothesized that deployment of a combination of four fatigue management technologies would result in increased sleep time (actigraph determined) under both Canadian hours-of-service (Study Phase 1) and U.S. hours-of-service (Study Phase 2). However, analyses of actigraphy data for sleep episodes in the NO FEEDBACK versus FEEDBACK conditions revealed no statistically significant differences in sleep duration in either the Canada study phase or the U.S. study phase (see "Prior Sleep" variable in Tables 13 and 24). "Prior Sleep" was defined by all the sleep time found in each 24-hour period (from noon to noon, across consecutive days in the 2-week period for each condition) using an actigraphic software program called "Action 4" (developed by Ambulatory Monitoring, Inc., Ardsley, NY), as well as software that could recognize and eliminate from consideration periods of time when the actigraph was not on the wrist of a driver.
Although the overall comparisons of actigraphically-defined 24-hour cumulative sleep time (Prior Sleep) were not different between the FEEDBACK and NO FEEDBACK conditions, it was clear that the U.S. study phase drivers had an average of 50 minutes less sleep per day than their Canadian counterparts during the NO FEEDBACK condition, and 39 minutes less sleep per day than their Canadian counterparts during the FEEDBACK condition (compare "Prior Sleep" in Tables 13 and 24). The reduced daily sleep times in the U.S. drivers were consistent with the differences between study phases in the predominant time-of-day for driving-Canada drivers had approximately 75% of their driving in daylight (and therefore, slept mostly in the nighttime), while U.S. drivers had approximately 90% of their driving at night (and therefore slept more in the daytime). It has long been established that sleep duration is reduced when people work nights, owing to circadian biological forces and environmental factors, which alone or together can truncate daytime sleep durations.
Analyses were performed to determine whether the actigraphically-defined sleep duration differences of 50 minutes (NO FEEDBACK difference between Canada and U.S.) and 39 minutes (FEEDBACK difference between Canada and U.S.) were statistically significantly different from each other. In addition, sleep durations would likely be affected by workdays and non-workdays, especially in the night driving U.S. subjects, such that non-workdays would likely involve significantly more sleep than workdays. As a result of these considerations, a series of analyses were conducted comparing actigraph-defined sleep obtained by Canada drivers and U.S. drivers on workdays and non-workdays, during the NO FEEDBACK 2-week period and the FEEDBACK 2-week period. These analyses yielded important new insights into the impact of FMT FEEDBACK on drivers' sleep durations. Tables 49 through 58, and Tables 7 through 9, display the results these analyses.
9.1 Sleep Durations on workdays and non-workdays
Tables 51, 52, 53, and 54 reveal that drivers slept significantly more on non-workdays than on workdays. During the NO FEEDBACK 2-week period of the Canada study phase, drivers averaged 7 hours and 17 minutes sleep per 24 hour period on non-workdays compared to 6 hours and 15 minutes on workdays (p = 0.023), a mean difference of 1 hours and 2 minutes (Table 51). Similarly, during the FEEDBACK 2-week period of the Canada study phase, drivers averaged 7 hours and 31 minutes of sleep per 24 hours on non-workdays compared to 6 hours and 14 minutes on workdays (p = 0.0005), a mean difference of 1 hour and 17 minutes (Table 53). Comparable results were obtained in the U.S. study phase. During the NO FEEDBACK 2-week period of Study Phase 2, the U.S. drivers averaged 6 hours and 32 minutes of sleep per 24 hours on non-workdays compared to 5 hours and 14 minutes on workdays (p = 0.018), a mean difference of 1 hour and 18 minutes (Table 52). Similarly, during the FEEDBACK period, U.S. drivers averaged 7 hours and 32 minutes sleep compared to 5 hours and 1 minute on workdays (p = 0.0004), a mean difference of 2 hours and 31 minutes (Table 54). These are relatively large differences in 24-hour sleep durations, suggesting that drivers developed sleep debts across the workweek.
Figure 7 graphically displays the workday versus non-workday sleep durations controlling for feedback condition. It reveals that the differences in mean daily sleep between workdays and non-workdays significantly differed between U.S. and Canada study phases (p = 0.028), which are referred to as "location" in Figure 7. Therefore, the NO FEEDBACK vs. FEEDBACK comparisons between U.S. and Canada were performed separately for workdays and non-workdays. Figure 8 reveals that during workdays, the NO FEEDBACK vs. FEEDBACK comparison did not significantly differ between U.S. and Canada study phases (p = 0.392) (Tables 55, 56, 57, 58). After removing the interaction, there was no main effect for feedback (p = 0.916), but mean sleep duration was significantly less for U.S. drivers compared to Canadian drivers (p = 0.011). Figure 9 shows that during non-workdays, the NO FEEDBACK vs. FEEDBACK comparison did not significantly differ between U.S. and Canada study phases (p = 0.506), and differences between U.S. and Canada were not significant during non-workdays (p = 0.460). Most importantly, in contrast to workdays, there was a significant increase in mean sleep duration during non-workdays in the FEEDBACK condition relative to the NO FEEDBACK condition (p = 0.046). In other words, FMT FEEDBACK resulted in drivers in both countries significantly increasing their non-workday daily sleep durations by an average of 45 minutes per day over what was the case in the NO FEEDBACK condition. This finding provides clear support for the hypothesis that a combination of four fatigue management technologies would result in more sleep (actigraph determined) under both Canadian hours-of-service (phase 1) and U.S. hours-of-service (phase 2).
While it might have been expected that increased sleep time would also have occurred on workdays when FMT FEEDBACK was provided, this did not occur. It is possible that workday schedules prevent drivers from acting on information from FMT devices indicating they need more sleep. Barriers to obtaining sleep may be absent on non-workdays, allowing drivers to increase sleep time. It remains uncertain if this pattern of increased sleep on non-workdays would be sustained over months and years with FMT FEEDBACK. Much more needs to be understood about the factors that determine when and where drivers obtain sleep on workdays and non-workdays, on the barriers to obtaining adequate sleep on workdays, and on the factors that convince them to get more recovery sleep on non-workdays. An average of 45 minutes (both study phases) more sleep per non-workday was associated with FMT FEEDBACK. While this may seem modest, research suggests it is especially beneficial in promoting recovery from chronic sleep debt in persons sleeping less than 6.5 hours per day, which was the case for virtually all drivers participating in the study during workday period.