Table 1.

—Select Sleep Parameter Definitions

Sleep latency	The amount of time it takes to initiate sleep once one is in bed and ready to sleep
NREM sleep	Includes stages 1 and 2 as well as slow wave sleep. The EEG is characterized by higher voltage and slower waves
Slow wave sleep	Previously termed stage 3 and 4 sleep. This EEG is characterized by delta waves. It is sometimes thought of as “deep sleep” or “restorative sleep”
REM sleep	A period of increased cortical activity and absent muscle tone aside from rapid eye movements. It is also a period where dreaming may take place. The EEG is defined by lower voltage, higher frequency theta activity
Sleep efficiency	The amount of time asleep divided by the total amount of time in bed