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Karolinska Sleepiness Scale (KSS)
Please email the author for information about obtaining the instrument: Dr. TorbjÖrn Åkerstedt,
Supplemental: Parkinson's Disease (PD)
Short Description of Instrument
The Karolinska Sleepiness Scale (KSS) is a self-report scale that measures the subject's drowsiness and is frequently used in studies measuring subjective sleepiness. The scale spans nine levels and asks the user to circle the number that represents the sleepiness level during the last five minutes.
Scoring and Psychometric Properties
Scoring: It is a 9-point verbally anchored scale going from 'extremely alert' to 'extremely sleepy-fighting sleep'. Scoring a seven or above is considered abnormal and indicative of daytime somnolence.
The nine levels are as follows:

  1. Extremely alert
  2. Very alert
  3. Alertt
  4. Rather alert
  5. Neither alert nor sleepy
  6. Some signs of sleepiness
  7. Sleepy, but no effort to keep awake
  8. Sleepy, some effort to keep awake
  9. Very sleepy, great effort to keep awake, fighting sleep
    Psychometric Properties: It has been validated against electroencephalography.
Strengths: Simple, fast, and easy to complete.
Weaknesses: Not widely used in PD. Only evaluates the five minutes prior to the test.
Key Reference:
Akerstedt T, Gillberg M. Subjective and objective sleepiness in the active individual. Int J Neurosci. 1990 May;52(1-2):29-37.

Additional Reference:
Kaida K, Takahashi M, Åkerstedt T, Nakata A, Otsuka Y, Haratani T, Fukasawa K. Validation of the Karolinska sleepiness scale against performance and EEG variables. Clinical Neurophysiology 2006 Jul;117(7):1574-81.
Document last updated August 2022