This variable is only available in MAP.

Interdaily stability is a measure of the strength of circadian rhythmicity, the degree of consistency of activity patterns from one day to the next. The variable is measured using a portable actigraph: AX3 (2020-present), GENEActiv (2018-2020), Actical (2005-2018). See the Actigraphy category description for detailed information on each device. Participants are asked to wear the actigraph 24 hours per day for up to 10 days.

Interdaily stability is the 24 hour value from a chi square periodogram, normalized for the number of data points. See reference for calculation. Values range from 0 to 1, with higher values indicating greater stability.

Note: Data is available for participants with at least one actigraphic recording of at least 7 consecutive days' duration.