Table 1

Sleep-related definitions

Sleep phaseThe sleep period from the time of day at sleep onset to the time of day on waking. It is dependent on the circadian process, and can be delayed or advanced by environmental or psychosocial factors.
Sleep patternThe consistency or lack of consistency in the sleep phase of an individual over consecutive days or weeks.
BedtimeThe time of day at which an individual goes to bed and attempts to sleep.
Sleep onsetThe time of day following bedtime at which sleep commences.
Wake timeThe time of day at which the final awakening from a sleep period occurs.
Time in bed (TIB)Total time spent in bed from bedtime to wake time.
Sleep period (SP)Total time from sleep onset to wake time.
Wake after sleep onset (WASO)Total time spent awake after the initial sleep onset and before final awakening (ie, WASO=SP–TST).
Total sleep time (TST)Total time spent sleeping (ie, TST=SP–WASO).
Sleep efficiencyTST expressed as a percentage of TIB (ie, TST/TIB × 100).
A measure of sleep quality.
Sleep onset latencyTime elapsed between bedtime and sleep onset.