Intra-individual daily and yearly variability in actigraphically recorded sleep measures: the CARDIA study

Sleep. 2007 Jun;30(6):793-6. doi: 10.1093/sleep/30.6.793.

Abstract

Study objectives: To describe the day-to-day and year-to-year variation in sleep characteristics among early middle-aged adults.

Design: Participants wore an Actiwatch (Mini Mitter, Inc) for 3 days on two occasions approximately 1 year apart.

Participants: N = 669 participants aged 38-50 years from the Chicago site of the Coronary Artery Risk Development in Young Adults (CARDIA) cohort study.

Measurements and results: Sleep measures included sleep duration, sleep latency, sleep efficiency, and time in bed. For each sleep parameter, total variance was decomposed into between-subject variance, within-subject variance from day to day, and within-subject variance from year to year. The standard deviation was calculated from the variance. Analysis yielded a within-subject daily standard deviation (SD) of 1.26 hours and a within-subject yearly SD of 0.39 hours for sleep duration. Daily SD was 30.7 minutes and yearly SD was 6.3 minutes for within-subject variability of sleep latency. Daily SD was 8.4% and yearly SD was 2.7% for within-subject variability of sleep efficiency. Finally, daily SD was 1.31 hours and yearly SD was 0.52 hours for within-subject variability of time in bed.

Conclusions: For each of the 4 sleep characteristics, nightly variability was much greater than yearly variability, meaning sleep behavior changes little in one year in this cohort of early middle-aged adults, despite large daily fluctuations. These results have important methodological implications, including that single-day measures of sleep may not accurately reflect habitual behavior.

Publication types

  • Research Support, N.I.H., Extramural

MeSH terms

  • Adult
  • Coronary Disease / epidemiology*
  • Female
  • Humans
  • Male
  • Middle Aged
  • Polysomnography / instrumentation*
  • Polysomnography / statistics & numerical data*
  • Severity of Illness Index
  • Sleep Wake Disorders / diagnosis*
  • Sleep Wake Disorders / epidemiology*
  • Time Factors