Comparison of two Japanese versions of the Karolinska Sleepiness Scale under partial sleep deprivation

The present study compared two Japanese translations of the Karolinska Sleepiness Scale (KSS). The original version was a 9-point Likert scale with descriptive terms for every other point (KSS-A). A modified version was later developed in which each point was accompanied by a descriptive term (KSS-B). The findings indicate subtle differences between the two Japanese versions of the KSS in their assessment of subjective sleepiness. Although these differences appear too small to meaningfully affect interchangeability, they may still have important implications for comparing results across studies and for the development of KSS-based sleepiness-detection devices.