]. Participants were recruited via 18 secondary schools across Cambridgeshire and Suffolk, UK from 2005 to 2006. At baseline, when participants were mean age 14·5 years , demographic and psychosocial measures were self-reported. Six months later, a sub-study was conducted focussing on diet, physical activity and body composition, in which participants completed a diet diary and simultaneously wore an activity monitor uninterrupted for four consecutive days.
]. Where sleep onset and sleep end times could not be ascertained from the activity plots, these cases were excluded. Prior to assessing sleep timings on this dataset, the researcher completed a training dataset discussing any discrepancies with a physical activity measurement specialist.Participants were provided with a 4-day diet diary to complete, which included two weekdays and two weekend days.