The subjects completed a sleep log every morning during seven
consecutive days. Questions included time of going to bed, time of
lights-out, estimated sleep onset latency, number and reason for
possible awakenings during the night, time of wake up, and subjective
sleep quality. The Time in Bed (TIB) variable was obtained by
calculating the time from lights-out to the wake-up time. During
weekdays, the average time of lights-out was 23 h 52 (range between
22 h 22 and 01 h 05). The average wake-up time was
6 h 52 (range between 4 h 51 and 9 h 43).