Table 1.

Definitions of the sleep–wake rhythm variables

Variable	Range	Definition
Intradaily variability	0–2	An estimate of the 24-hour rest-activity rhythm and reflects the fragmentation of the rhythm, a higher intradaily variability indicates a more fragmented rhythm
Interdaily stability	0–1	An estimate of the stability of the rhythm, and describes the synchronization of the rhythm, wherein 1 signifies a perfect synchronization to the light-dark cycle
L5 counts	0–∞	Activity counts of the least active 5 hours of the day.
M10 counts	0–∞	Activity counts of the most active 10 hours of the day.
Relative amplitude	0–1	Ratio of the difference and the sum of M10 and L5 counts. A higher relative amplitude indicates a bigger difference between the least and most active period during the day, hence a better sleep–wake rhythm.