No abstract

SUMMARYAlthough adolescents often experience insufficient and ⁄ or poor sleep, sleep variables such as total sleep time do not account for individualsÕ sleep need and sleep debt and may therefore be an inadequate representation of adolescentsÕ sleep problems and its daytime consequences. This problem can be overcome by using the Chronic Sleep Reduction Questionnaire (CSRQ), an assessment tool that measures symptoms of chronic sleep reduction and therefore accounting for sleep need and sleep debt. The present study aims at developing an English version of the CSRQ and assesses the reliability and validity of the Dutch and the English CSRQ version. The CSRQ was administered in large Dutch (n = 166, age = 15.2 ± 0.57 years, 28% male) and Australian (n = 236, age = 15.5 ± 0.99 years, 65% males) samples. Subjective sleep variables were measured with surveys and sleep diaries of five school nights. Additionally, sleep of the same five nights was monitored with actigraphy. Both CSRQ versions showed good psychometric properties concerning their reliability (Dutch: a = 0.85; English: a = 0.87) and validity as the same overall structure of the two CSRQ versions and significant correlations with subjective and objective sleep variables were found. School grades were related to chronic sleep reduction, whereas the relationship between grades and other sleep variables was weak or absent. These results highlight the idea that chronic sleep reduction may be a better indicator of adolescentsÕ insufficient and ⁄ or poor sleep than other sleep variables such as total sleep time. IN TROD UCTI ONAdolescents sleep less than younger children, although it has been shown that their objective need for sleep does not decrease during the pubertal transition (Carskadon et al., 1993). Eleven to 47% of adolescents report poor sleep (Liu and Zhou, 2002;Russo et al., 2007), and more than 50% sleep less than the ideal 9 h per night (Gibson et al., 2006). This phenomenon can be caused by an interaction of intrinsic (e.g. puberty, circadian and ⁄ or homeostatic changes) and extrinsic factors (e.g. social pressure, academic workload) causing later bedtimes, while rise times remain unchanged due to early school start times (Wolfson and Carskadon, 2003). As most adolescents experience these sleep problems over a long period of time, it can be assumed that many suffer from chronically reduced sleep (Loessl et al., 2008;Meijer, 2008). Over time, chronic sleep reduction can result in severe psychological and physiological consequences such as behavioural problems, poor emotional wellbeing, impaired cognitive and school performance and even detrimental neurobiological changes (Curcio et al., 2006;Mitru et al., 2002;Moore and Meltzer, 2008;Wolfson and Carskadon, 2003).The problem of chronic sleep reduction during adolescence is a worldwide existing and well-known phenomenon. However, due to a lack of consensus concerning the

STUDY OBJECTIVE To test whether sleep duration on school nights differs between adolescents in Australia and the U.S. and, if so, whether this difference is explained by cultural differences in school start time, parental involvement in setting bedtimes and extra-curricular commitments. PARTICIPANTS 385 adolescents aged 13-18 years (M=15.57,SD=0.95; 60% male) from Australia and 302 adolescents aged 13-19 years (M=16.03, SD=1.19; 35% male) from the United States. METHODS Adolescents completed the School Sleep Habits Survey during class time, followed by an 8-day Sleep Diary. RESULTS After controlling for age and sex, Australian adolescents obtained an average of 47 minutes more sleep per school night than those in the U.S. Australian adolescents were more likely to have a parent-set bedtime (17.5% vs 6.8%), have a later school start time (8:32am vs 7:45am) and spend less time per day on extra-curricular commitments (1h37m vs 2h41m) than their U.S. peers. The mediating factors of parent-set bedtimes, later school start times, and less time spent on extra-curricular activities were significantly associated with more total sleep. CONCUSIONS In addition to biological factors, extrinsic cultural factors significantly impact upon adolescent sleep. The present study highlights the importance of a cross-cultural, ecological approach and the impact of early school start times, lack of parental limit setting around bedtimes and extracurricular load in limiting adolescent sleep.

This prospective quasi-experiment (N = 175; mean age = 15.14 years) investigates changes in adolescents' sleep from low-stress (regular school week) to high-stress times (exam week), and examines the (moderating) role of chronic sleep reduction, baseline stress, and gender. Sleep was monitored over three consecutive weeks using actigraphy. Adolescents' sleep was more fragmented during the high-stress time than during the low-stress time, meaning that individuals slept more restless during stressful times. However, sleep efficiency, total sleep time, and sleep onset latency remained stable throughout the three consecutive weeks. High chronic sleep reduction was related to later bedtimes, later sleep start times, later sleep end times, later getting up times, and more time spent in bed. Furthermore, low chronic sleep reduction and high baseline stress levels were related to more fragmented sleep during stressful times. This study shows that stressful times can have negative effects on adolescents' sleep fragmentation, especially for adolescents with low chronic sleep reduction or high baseline stress levels.