Table 1.

Definitions of Sleep/Wake, Activity/Rest, and Circadian Rhythm Parameters Obtained with Actigraphy*

Variable	Definition
Sleep onset latency (SOL)	Number of minutes between when someone lays down to sleep and actually goes to sleep (measure of sleep initiation)
Percent wake at night	Percentage of time awake after sleep onset during a sleep period (measure of sleep maintenance)
Number of awakenings	Total number of awakenings during a sleep period
Wake duration	Number of minutes per awakening
Total sleep time	Total sleep time while in bed; number of minutes of sleep while in bed
Sleep period time	Total number of minutes in bed
Sleep efficiency (SE)	The number of minutes of sleep divided by the total number of minutes in bed, multiplied by 100
Total sleep time/day	Number of minutes asleep during the day from 9:00 to 20:59
Total wake time/day	Number of minutes awake during the day from 9:00 to 20:59
Sleep percent of day	Percentage of time asleep during the day from 9:00 to 20:59
Wake percent of day	Percentage of time awake during the day from 9:00 to 20:59
Mesor	24 hour rhythm adjusted mean of activity counts; higher values represent more robust activity
Amplitude	Peak (or trough) value of the cosine curve minus the mesor; represents the rhythmic change of an individual activity during the 24-hour period
Peak activity	Sum or the mesor and amplitude values; it represents more robust circadian activity rhythms
Acrophase	Actual clock time of the peak amplitude
Circadian quotient	Strength of the circadian rhythm, calculated by dividing the amplitude by the mesor.
Autocorrelation	Comparison of the regularity and consistency of the rhythm from one day to the next day