Intraindividual Variability and Temporal Stability of Mid-Sleep on Free and Workdays

Abstract

People differ in their sleep timings that are often referred to as a chronotype and can be operationalized as mid-sleep (midpoint between sleep onset and wake-up). The aims of the present studies were to examine intraindividual variability and longer-term temporal stability of mid-sleep on free and workdays, while also considering the effect of age. We used data from a 2-week experience sampling study of British university students (Study 1) and from a panel study of Estonian adults who filled in the Munich Chronotype Questionnaire twice up to 5 years apart (Study 2). Results of Study 1 showed that roughly 50% of the variance in daily mid-sleep scores across the 14-day period was attributed to intraindividual variability as indicated by the intraclass correlation coefficient. However, when the effect of free versus workdays was considered, the intraindividual variability in daily mid-sleep across 2 weeks was 0.71 the size of the interindividual variability. In Study 2, mid-sleep on free and workdays showed good levels of temporal stability—the retest correlations of mid-sleep on free and workdays were 0.66 and 0.58 when measured twice over a period of 0-1 to 5 years. The retest stability of mid-sleep scores on both free and workdays sharply increased from young adulthood and reached their peak when participants were in late 40 to early 50 years of age, indicating that age influences the stability of mid-sleep. Future long-term longitudinal studies are necessary to explore how age-related life circumstances and other possible factors may influence the intraindividual variability and temporal stability of mid-sleep.

Personality traits relate to chronotype at both the phenotypic and genetic level

“…The dataset, or parts of it, has been used in other studies (e.g., Kööts-Ausmees et al, 2016;Lenneis et al, 2020;Realo et al, 2015Realo et al, , 2017, but it has not been used for the present purpose.…”

Sleep variability and regularity as contributors to obesity and cardiometabolic health in adolescence

“…One hour of irregularity in the timing of the sleep midpoint is considered abnormal for a typical adolescent [27]. Like sleep variability, sleep irregularity decreases with age, particularly from young to middle adulthood [53].…”

“…Alternatively, in scenarios in which rising time (out‐of‐bed) data, but not wake‐up time (final awakening) data, are available, the formula sleep midpoint = sleep onset time + (total sleep time)/2, may be used (Table 1) [52]. As with sleep duration, the sleep midpoint also shows nightly deviations, and this irregularity in the circadian timing of sleep appears to peak in adolescence [26, 53]. There are several different metrics used to quantify sleep regularity (Table 1), which include the intraindividual standard deviation (StDev) in sleep midpoint as calculated through actigraphy and/or sleep logs, interdaily stability, which is more reflective of rest‐activity rhythms as compared with sleep–wake patterns [26], social jetlag to measure average sleep patterns between weekdays and weekends, composite phase deviation, the sleep regularity index, and sleep onset time, as well as wake‐up time, to name a few [26].…”

“…One hour of irregularity in the timing of the sleep midpoint is considered abnormal for a typical adolescent [27]. Like sleep variability, sleep irregularity decreases with age, particularly from young to middle adulthood [53]. As shown in Table 2, Kramer, Kerkhof, and Hofman also found that younger males showed greater day‐to‐day StDev in their sleep midpoint (i.e., greater sleep irregularity) as compared with older males, suggesting that research should examine maturational periods and developmental changes across the life‐span in relation to irregularity in the circadian timing of sleep [54].…”

Physical activity, sleep and affective wellbeing on the following day: An experience sampling study

“…In line with such a mediation model, experimental and intervention studies show that exercise has an acute beneficial effect on sleep duration, sleep quality and sleep continuity the following night (Kline et al, 2021; Kredlow et al, 2015). Furthermore, analyses of time series data using experience sampling methods (ESMs) show that indicators of sleep quality are positively associated with positive affect and negatively with negative affect the next day (Das‐Friebel et al, 2020; Konjarski et al, 2018; Lenneis et al, under review). Thus, based on these two lines of evidence, it is possible that physical activity exerts its positive effect on mental health at least partly via improved sleep quality as a mediator.…”