Introduction Sleepiness Is the Craving or Desire for Sleep and Is the Physiological Drive That Promotes the Onset of Sleep1 and Reflects the Balance between Sleep

SLEEPINESS IS THE CRAVING OR DESIRE FOR SLEEP AND IS THE PHYSIOLOGICAL DRIVE THAT PROMOTES THE ONSET OF SLEEP1 AND REFLECTS THE BALANCE BETWEEN SLEEP DRIVE AND AROUSAL.2 The degree of sleepiness may be estimated objectively using the multiple sleep latency test (MSLT), which measures the time to sleep onset evident in the electroencephalogram.3 The MSLT has been used extensively to measure the extent of daytime sleepiness in patients with sleep disorders, particularly narcolepsy, as well as sleep propensity in research settings.4,5 The MSLT is sensitive to partial sleep deprivation and the cumulative effects of sleep restriction.6 A modification of the MSLT, the Maintenance of Wakefulness Test, is used to quantify the ability to remain awake and has been used to evaluate treatment efficacy in patients with excessive somnolence.7 Although these electroencephalographic techniques provide the most accurate measurements of sleepiness, they are inappropriate for largescale epidemiologic studies and some fieldwork. Subjective perceptions of sleepiness are reasonable indicators of physiological sleepiness and may even precede performance decrements.8 Generally, we are able to recognize how sleepy we are, though misjudgment of sleepiness may occur with prolonged sleep restriction.6 Subjective measures of instantaneous perceived sleepiness, such as those reflected in the Karolinska Sleepiness Scale (KSS)9 and the Stanford Sleepiness Scale (SSS),10 are quick and simple to complete, provided that the subjects have some level of literacy and comprehension of what is required. Visual analog scales (VAS),11-15 which are simple, cheap, and easy to execute, also have been used to assess sleepiness.8,9,16,17 However, indicating a response on a VAS requires some understanding of geometry and the ability to map an abstract phenomenon onto a VAS. The concept of a scale, even one as simple as the VAS, may be foreign to children at a prelogical cognitive stage of development. Also, preliminary studies in our laboratory have indicated that poorly educated and, especially, rural people fail to understand the concept of a VAS. Conceptually, the measurement of perceived sleepiness is a task similar to the measurement of perceived pain. Pictorial scales, using cartoon faces, are well established as instruments for measuring perceived pain in subjects and patients for whom semantic or geometric scales are inappropriate and, particularly, for children.18 We therefore designed a pictorial scale, using cartoon faces, to measure perceived sleepiness and tested it using, as a subject base, a diverse South African adult population that included many subjects whose home language was not English and South African preschool and junior-school children. We also validated the scale against established scales and assessed its utility in practical applications.