Odds ratio product of sleep EEG as a continuous measure of sleep state

Sleep. 2015 Apr 1;38(4):641-54. doi: 10.5665/sleep.4588.


Study objectives: To develop and validate an algorithm that provides a continuous estimate of sleep depth from the electroencephalogram (EEG).

Design: Retrospective analysis of polysomnograms.

Setting: Research laboratory.

Participants: 114 patients who underwent clinical polysomnography in sleep centers at the University of Manitoba (n = 58) and the University of Calgary (n = 56).

Interventions: None.

Measurements and results: Power spectrum of EEG was determined in 3-second epochs and divided into delta, theta, alpha-sigma, and beta frequency bands. The range of powers in each band was divided into 10 aliquots. EEG patterns were assigned a 4-digit number that reflects the relative power in the 4 frequency ranges (10,000 possible patterns). Probability of each pattern occurring in 30-s epochs staged awake was determined, resulting in a continuous probability value from 0% to 100%. This was divided by 40 (% of epochs staged awake) producing the odds ratio product (ORP), with a range of 0-2.5. In validation testing, average ORP decreased progressively as EEG progressed from wakefulness (2.19 ± 0.29) to stage N3 (0.13 ± 0.05). ORP < 1.0 predicted sleep and ORP > 2.0 predicted wakefulness in > 95% of 30-s epochs. Epochs with intermediate ORP occurred in unstable sleep with a high arousal index (> 70/h) and were subject to much interrater scoring variability. There was an excellent correlation (r(2) = 0.98) between ORP in current 30-s epochs and the likelihood of arousal or awakening occurring in the next 30-s epoch.

Conclusions: Our results support the use of the odds ratio product (ORP) as a continuous measure of sleep depth.

Keywords: ORP; Sleep quality; odds ratio product; sleep depth; sleep staging.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adult
  • Aged
  • Aged, 80 and over
  • Alberta
  • Algorithms
  • Arousal / physiology
  • Brain Waves / physiology
  • Electroencephalography*
  • Female
  • Humans
  • Male
  • Manitoba
  • Middle Aged
  • Odds Ratio
  • Polysomnography
  • Reproducibility of Results
  • Retrospective Studies
  • Sleep / physiology*
  • Sleep Stages / physiology
  • Wakefulness / physiology
  • Young Adult