Háskóli ÍslandsUniversity of IcelandBrychta, Robert J.Rögnvaldsdóttir, VakaGudmundsdottir, Sigridur LaraStefansdottir, RunaHrafnkelsdóttir, Soffía MargrétGestsdottir, SunnaArngrímsson, Sigurbjörn ÁrniChen, Kong Y.Jóhannsson, Erlingur2021-03-082021-03-082019-12-01Brychta, R. J., Rögnvaldsdóttir, V., Guðmundsdóttir, S. L., Stefánsdóttir, R., Hrafnkelsdóttir, S. M., Gestsdóttir, S., Arngrímsson, S. A., Chen, K. Y., & Jóhannsson, E. (2019). Longitudinal Change in Adolescent Bedtimes Measured by Self-Report and Actigraphy, Journal for the Measurement of Physical Behaviour, 2(4), 282-287. Retrieved Mar 4, 2021, from https://journals.humankinetics.com/view/journals/jmpb/2/4/article-p282.xml2575-66052575-6613 (eISSN)https://hdl.handle.net/20.500.11815/2488Introduction: Sleep is often quantified using self-report or actigraphy. Self-report is practical and less technically challenging, but prone to bias. We sought to determine whether these methods have comparable sensitivity to measure longitudinal changes in adolescent bedtimes. Methods: We measured one week of free-living sleep with wrist actigraphy and usual bedtime on school nights and non-school nights with self-report questionnaire in 144 students at 15 y and 17 y. Results: Self-reported and actigraphy-measured bedtimes were correlated with one another at 15 y and 17 y (p < .001), but reported bedtime was consistently earlier (>30 minutes, p < .001) and with wide inter-method confidence intervals (> ±106 minutes). Mean inter-method discrepancy did not differ on school nights at 15 y and 17 y but was greater at 17 y on non-school nights (p = .002). Inter-method discrepancy at 15 y was not correlated to that at 17 y. Mean change in self-reported school night bedtime from 15 y to 17 y did not differ from that by actigraphy, but self-reported bedtime changed less on non-school nights (p = .002). Two-year changes in self-reported bedtime did not correlate with changes measured by actigraphy. Conclusions: Although methods were correlated, consistently earlier self-reported bedtime suggests report-bias. More varied non-school night bedtimes challenge the accuracy of self-report and actigraphy, reducing sensitivity to change. On school nights, the methods did not differ in group-level sensitivity to changes in bedtime. However, lack of correlation between bedtime changes by each method suggests sensitivity to individual-level change was different. Methodological differences in sensitivity to individual- and group-level change should be considered in longitudinal studies of adolescent sleep patterns.282-287eninfo:eu-repo/semantics/openAccessAccelerometerQuestionnaireSleepSleep onsetTeenagersUnglingarSvefnvenjurSvefnSpurningalistarinfo:eu-repo/semantics/articleJournal for the Measurement of Physical Behaviour10.1123/jmpb.2019-0021