Table 1b.

Commonly assessed sleep variables.

Sleep or circadian variable	Definition
Sleep latency	Time from lights out until first occurrence of sleep
Sleep Period Time (SPT)	Time from sleep onset until final awakening, including intermittent waking periods
Total Sleep Time (TST)	Total time spent in any REM or NREM sleep stage
Sleep efficiency	Percentage of time in bed (TIB) spent asleep
REM onset latency	Time between sleep onset and the first occurrence of REM
REM density	Measure of frequency of rapid eye movements during REM sleep
Slow wave sleep	Amount of non-REM sleep stages 3 and 4 (also known as delta sleep)