Sleep efficiency (SE) is the ratio between the time a person spends asleep, and the total time dedicated to sleep (i.e. both sleeping and attempting to fall asleep or fall back asleep).
[2][better source needed] SE can be determined with a polysomnograph and is an important parameter of a sleep study.
[3] Sleep efficiency is often described as the ratio between time spent asleep ("total sleep time (TST)"), and time spent "in bed" ("time in bed (TIB)"), however, TIB does not encompass "non-sleep-related activities" performed in bed (e.g. reading, watching television, etc.)
[4] SE is significantly reduced in insomnia; SE is therefore an important clinical parameter in clinical investigations of insomnia.
[5] Furthermore, lower values of SE are often observed in sleep studies on pregnant populations and are mostly explained by the increased awakening periods after sleep onset (''wake after sleep onset (WASO)'').