# What is the role of normative sleep stage data in sleep stage scoring?

Updated: Aug 19, 2019
• Author: Andres A Gonzalez, MD, MMM, FACNS; Chief Editor: Selim R Benbadis, MD  more...
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Normative values have been constructed based on sleep staging results to help quantify the composition and quality of sleep. Normative data change with age and vary from center to center. In addition, most were collected using the R and K rules.

The AASM manual has recommended recording the values listed below.

For the purposes of illustration, normative data for different age groups is presented (see Table 1 below). It is important to note that “normal” sleep varies greatly by age with a large decrease in the amount of REM sleep from infancy to young adulthood and other significant decreases in slow wave sleep, sleep efficiency, and total sleep time with advancing age.

Total Sleep Time (TST) = Total minutes of sleep = Stage N1 + N2 + N3 + stage R.

Time in Bed (TIB) or total recording time = Monitoring period = Lights out to lights on.

Sleep Latency (SL) = Total number of minutes from lights out to sleep onset.

Stage R Latency = Time from sleep onset to first epoch of REM sleep.

Wake After Sleep Onset (WASO) = Minutes of Stage W that occur throughout the night after initial sleep onset and before the final awakening.

Sleep Efficiency (%) = (TST/TIB) x100%.

Total Time in Each Stage = Separate values for stage N1, N2, N3, and R.

Percent of TST in Each Stage = (Time in each stage/TST) x 100%

Table 1. Normative Sleep Stage Data Across Age Groups.* (Open Table in a new window)

 Age (y) 20-29 30-39 40-49 50-59 >60 TST (min) 374.9 375.8 370.2 366.6 348.8 Sleep Efficiency (%) 94.4 94.4 90.2 90.4 85.8 Sleep Latency (min) 6.3 10.0 8.4 6.1 8.2 Number of Awakenings 6.3 4.7 8.4 9.7 12.3 Stage R (%TIB) 22.2 23.1 20.4 20.9 16.4 Stage N1 (%TIB) 3.0 2.5 4.3 4.7 4.0 Stage N2 (%TIB) 50.5 52.8 54.6 56.7 57.6 Stage N3 (%TIB) 18.8 16.1 10.9 8.1 7.7 Adapted from Hirshkowitz M. Normal human sleep: an overview. Med Clin North Am. May 2004;88(3):551-65. [14]

These values are useful in the diagnosis and management of sleep disorders. For example, increased sleep latency may be increased in primary insomnia and decreased in obstructive sleep apnea, whereas Stage R latency may be decreased in narcolepsy.

Sleep architecture changes with advancing age. The percentage of stage R is greatest in neonates, where it may encompass 50% of total sleep time. This proportion decreases gradually to 20-25% at adolescence, with further slight decrease after age 65.

Greater sleep fragmentation also occurs with aging, such that wakefulness is intermixed with sleep. The percentage of Stage N3 sleep decreases with age while percentages of time spent in N1, N2, and WASO increase. To some degree, N3 sleep may decrease in advancing age because of lesser EEG amplitudes resulting in sub-threshold, values that will not be scored during analysis. Due to this combination of factors, some elderly individuals may have significantly decreased N3 sleep, however, some degree will be due to lack of detection.