Sleep efficiency

Sleep efficiency is the ratio between the time a person spends asleep, and the total time dedicated to sleep. It is given as a percentage. SE of 80% or more is considered normal/healthy with most young healthy adults displaying SE above 90%. SE can be determined with a polysomnograph and is an important parameter of a sleep study.
Sleep efficiency is often described as the ratio between time spent asleep, and time spent "in bed", however, TIB does not encompass "non-sleep-related activities" performed in bed as the phrase may seem to suggest.

Clinical significance

Long sleep duration may be a sign of low sleep efficiency. SE is significantly reduced in insomnia; SE is therefore an important clinical parameter in clinical investigations of insomnia. SE declines with age and low SE is common in the elderly. 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.