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The study objective was to validate the Karolinska Sleep Questionnaire with regard to dimensionality, internal consistency, and construct and criterion validity. Another objective was to provide normative data. Data from the cross-sectional Västerbotten Environmental Health Study in Sweden were used. The 3406 participants in this study, 18 to 79 years old, constituted a random sample stratified for age and sex. Along with the Karolinska Sleep Questionnaire, the participants responded to the Hospital Anxiety and Depression Scale, the Perceived Stress Scale, and the Shirom Melamed Burnout Questionnaire for assessing construct validity. Factor analyses of the questions in the Karolinska Sleep Questionnaire that relate to nocturnal sleep revealed the dimensions sleep quality, non-restorative sleep, and sleep apnea. A separate factor analysis on the questions regarding day time sleepiness revealed a sleepiness dimension. The sleep quality, non-restorative sleep, and sleepiness dimensions showed approximate normal distributions, whereas the distribution for sleep apnea was positively skewed. All dimensions showed good internal consistency. Satisfactory construct validity was found for all dimensions. Using the DSM-IV criteria of insomnia, relevant questions in the Karolinska Sleep Questionnaire were combined into an index of nocturnal symptoms of insomnia as were questions of sleep apnea. Prevalences of insomnia and sleep apnea correspond well to those of other studies, indicating good criterion validity. The favorable psychometric properties of the dimensions and indexes from the Karolinska Sleep Questionnaire suggest their use for assessing sleep quality, non-restorative sleep, sleep apnea, sleepiness and nocturnal symptoms of insomnia. [ABSTRACT FROM AUTHOR]

Sleepiness is a major cause of lower productivity and higher risk of accidents in various work situations. Developing sleepiness monitoring techniques is important to improve work efficiency and to reduce accident risk, so that people can take a rest/break in appropriate timing before an accident or a mistake occurs. The aims of the present study are (1) to explain subjective sleepiness using sleep-related symptoms, and (2) to examine which symptoms are useful to predict performance errors. Participants were healthy paid volunteers (six males, six females; mean ± SD, 31.5 ± 10.74 years). Participants took part in 26-h sleep deprivation. During sleep deprivation, they carried out several performance tasks every 3 h and an hourly rating of questionnaires to evaluate subjective symptoms including two types of Karolinska sleepiness scale (KSS). The present study confirmed that performance errors can be predicted by subjective symptoms. While mental fatigue was correlated to KSS scores linearly, eye-related subjective symptoms showed quadratic correlations to KSS. By taking into consideration this noteworthy relationship between subjective symptoms and sleepiness, more accurate introspection of sleepiness and performance errors prediction (detection) may be possible. [ABSTRACT FROM AUTHOR]

The Karolinska Sleepiness Scale (KSS) is frequently used to study sleepiness in various contexts. However, it exists in two versions, one with labels on every other step (version A), and one with labels on every step (version B) on the 9-point scale. To date, there are no studies examining whether these versions can be used interchangeably. The two versions were here compared in a 24 hr wakefulness study of 12 adults. KSS ratings were obtained every hour, alternating version A and B. Results indicated that the two versions are highly correlated, do not have different response distributions on labeled and unlabeled steps, and that the distributions across all steps have a high level of correspondence (Kappa = 0.73). It was concluded that the two versions are quite similar. [ABSTRACT FROM AUTHOR]

A correction to the article "Comparing two versions of the Karolinska Sleepiness Scale (KSS)" that was published in the July 28, 2017 issue, is presented.