Actigraphy-derived sleep fragmentation index: convergent validity and associations with clinical outcomes.

Study Objectives: Wake after sleep onset and sleep efficiency derived from actigraphy are common assessments of sleep fragmentation (or continuity). The sleep fragmentation index (SFI), measuring the frequency of sleep-wake transitions, is less understood. This study examined (1) the convergent validity between SFI and other sleep metrics obtained by actigraphy and polysomnography; and (2) associations of SFI with sleep symptoms, obstructive sleep apnea, periodic limb movement index, and cognition (Digit Symbol Coding test).

Methods: Cross-sectional analysis using logistic and multiple regression analyses adjusted for potential confounders. 1,908 participants in the Multi-Ethnic Study of Atherosclerosis study who underwent 7-day actigraphy and polysomnography. The sample was 53.9% female; age 68.3 ± 9.1 years (mean ± standard deviation); apnea-hypopnea index 19.5 ± 17 events/h; and SFI 20.09 ± 6.99.

Results: Higher SFI was associated with older age, male sex, Black race, smoking, body mass index, obstructive sleep apnea, and polysomnography-based metrics of sleep architecture. SFI was strongly correlated with actigraphy-measured sleep efficiency ( = -.75; < .0001) and wake after sleep onset ( = .63; < .0001), and modestly correlated with polysomnography-wake after sleep onset, apnea-hypopnea index, and arousal index (s = 0.23-0.27; s < .0001). In adjusted analyses, each standard deviation unit increase in SFI was associated with 1.1-1.4 higher odds of insomnia symptoms, sleepiness, obstructive sleep apnea, an elevated periodic limb movement index, and with lower Digit Symbol Coding test scores ( < .05).

Conclusions: The results support the convergent validity between actigraphy-estimated SFI and actigraphy-wake after sleep onset and sleep efficiency. SFI showed modestly stronger associations with clinical symptoms compared to other fragmentation variables, supporting its utility as a marker of sleep continuity.

Citation: Saleh D, Bertisch SM, Reid M, Lim A, Purcell S, Redline S. Actigraphy-derived sleep fragmentation index: convergent validity and associations with clinical outcomes. . 2025;21(9):1557-1565.