Karolinska Sleepiness Scale
The Karolinska Sleepiness Scale is a 9-point subjective scale used to assess a person's current level of sleepiness or alertness. It asks respondents to rate how sleepy or alert they feel at the moment on a scale from 1 to 9. The scale is situational, meaning it reflects sleepiness at a particular time and can change hour by hour. It was developed by and Mats Gillberg at the Karolinska Institute in Sweden. Because of its simplicity and sensitivity to changes, KSS is used in sleep and fatigue research.
History
The KSS was introduced by Åkerstedt and Gillberg in 1990 as a unidimensional sleepiness rating scale. In their original work it was validated against brain electrical activity: higher KSS scores were strongly associated with increases in EEG alpha/theta power and slow eye movements. Over time, it became popular for tracking short-term changes in alertness during sleep studies, shift work experiments, and fatigue research.There are two versions of KSS: one with labels on every point and one with labels only on alternate points; studies have found the two versions yield essentially the same results.
Scale
The KSS is scored from 1 to 9 with intermediate descriptors. Each number corresponds to a verbal description of alertness level. In one commonly used version, the labels are:1 = extremely alert2 = very alert3 = alert4 = rather alert5 = neither alert nor sleepy6 = some signs of sleepiness7 = sleepy but no effort to keep awake8 = sleepy and some effort to keep awake9 = very sleepy, great effort to keep awake, fighting sleepHigher KSS scores indicate greater sleepiness. In practice, KSS ratings are often collected repeatedly to monitor how sleepiness changes over time. Typical findings are that KSS scores rise with longer wakefulness and vary with the time of day