Actigraphy Data Collection

An Actiwatch Spectrum (Philips Respironics, Murrysville, PA) wrist actigraph was placed on the nondominant wrist and participants were asked to keep the device on the wrist continuously for 7 days with activity and light data collected in 30-second epochs. Participants also completed a sleep diary upon awakening each day. A centralized reading center in Boston, MA, scored all records. Rest periods where the participant was trying to sleep were identified following a standardized protocol that made use of event markers, sleep diaries, light exposure, and activity levels.²⁵ Sleep–wake status for each 30-second epoch within each rest period was computed using the Actiware 5.59 scoring algorithm with sleep onset defined based on 5 immobile minutes, 0 immobile minutes for sleep offset, and a wake threshold of 40 counts. The scoring algorithm has been validated against polysomnography on an epoch-by-epoch basis.^26–28 Participants with at least 5 days of valid actigraphy data were included for the analysis.