Table 1.

24-h rest–activity rhythm parameters

Acrophase	The time of peak activity
Amplitude	Difference between the model fitted peak value and the mesor
Mesor	The mean activity of the fitted 24-h pattern
Relative amplitude	Refers to the difference between the maximum (or minimum) value of the fitted cosine function and mesor and is a normalized measure of rhythm strength accounting for average activity levels
Circadian Function Index (CFI)	A numerical index that determines the circadian robustness, based on three circadian parameters: interday stability, intraday variability, and relative amplitude. CFI oscillates between 0 (absence of circadian rhythmicity) and 1 (robust circadian rhythm)
L5 midpoint	Timing of the least active 5-h period, an indicator of midpoint of sleep
M10 midpoint	Timing of the most active 10-h period
Interday stability	An estimate of how closely the 24-h rest–activity rhythm follows the 24-h light–dark cycle. Determines the consistency of the 24 h rhythmic pattern over days. A stable rhythm is characterized by a 24-hour profile that remains very similar from day to day
Intraday variability	Fragmentation of the rhythm. Its values oscillate between 0 when the wave is perfectly sinusoidal and 2 when the wave describes a Gaussian noise