How much does sleep vary from night-to-night? A quantitative summary of intraindividual variability in sleep by age, gender, and racial/ethnic identity across eight-pooled datasets

Abstract

Study Objectives: Habitual sleep duration and efficiency vary widely by age, gender, and racial/ethnic identity. Despite growing research on the importance of night-to-night, intraindividual variability (IIV) in sleep, few studies have examined demographic differences in sleep IIV. The present study describes typical sleep IIV overall and by demographics among healthy sleepers. Methods: Eight international data sets of healthy sleepers (N = 2404; 26,121 total days of sleep data) were synthesized to examine age, gender, and racial/ethnic identity differences in sleep IIV measured via diaries, actigraphy, and electroencephalography. Sleep IIV estimates included the intraindividual standard deviation (iSD), root mean square of successive differences (RMSSD), coefficient of variation (CV), and a validated Bayesian Variability Model (BVM). Results: Sleep duration and efficiency varied widely from night-to-night within people (duration iSD: 67.04–85.80 minutes; duration RMSSD: 91.93–118.91 minutes; duration CV: 18.57–19.19%; duration BVM: 48.60–60.60 minutes; efficiency iSD: 5.18–6.46%, efficiency RMSSD: 7.01–8.44%; efficiency CV: 5.80–8.14%; efficiency BVM: 3.40–4.16%). Different metrics of IIV were strongly correlated for sleep duration (rs .58–.97) and sleep efficiency (rs .53–1.00). Younger adults had more IIV in diary and actigraphy sleep duration. Gender differences were inconsistent. White and non-Hispanic/Latinx adults had less IIV in sleep duration and efficiency compared to racial/ethnic minority groups. Conclusions: Even among healthy sleepers, sleep varies widely from night-to-night. Like mean sleep, there also may be disparities in IIV in sleep by demographic characteristics. Study results help characterize normative values of sleep IIV in healthy sleepers.