Development of a Scale for Assessing Three Aspects of Sleep: Regularity, Quality, and Quantity

Objectives: It is difficult to assess sleep habits using one factor (i.e., sleep duration) alone. Regularity and quality of sleep have to be considered to assess sleep accurately. However, to our knowledge there is no scale which scores the three factors simultaneously. The purpose of this study was to inspect the reliability and validity (content, construct, and discriminant validity) of a scale we developed to screen for poor sleep habits. This scale was constructed to assess three aspects of sleep: regularity, quality, and quantity. Methods: Subjects were 563 day workers (370 men and 193 women; average age = 40.4 yr) from the manufacturing and service industries. We created a 21-item questionnaire (7 items for each of 3 factors) based on earlier studies and discussions with specialists. Reliability and construct validity of the questionnaire were assessed through item and factor analyses and Cronbach's alpha. In addition, subjects' scores were using principal component analysis, and subjects were classified according to their scores through a cluster analysis. We compared lifestyles, daytime sleepiness, stress, and chronic disease among the subjects to examine the instrument's discriminant validity. Results: Although our analysis revealed 6 items were invalid, the questionnaire assessed the three factors (regularity, quality and quantity) as expected: Cronbach's alpha was 0.744, 0.757, and 0.548, respectively. Two of the 7 quantity items were identified as assessing regularity instead, but all other items performed as expected. Four items measuring insomnia (disturbance of sleep induction, disturbance of sound sleep, nocturnal awakening, and early morning awakening) included constant burden as a quality factor. Chi-squared tests showed that the ratio of participants who took good care of their health and had less stress and daytime sleepiness was significantly high in the highest-scoring group, while the ratio of people reporting stress and chronic disease was significantly high in the lowest-scoring group. Conclusions: The questionnaire we developed for assessing three factors of sleep (regularity, quality and quantity) was determined to have construct validity. However, since some items were excluded and some assessed into another factor, sufficient reliability and content validity were not found. Revision is needed to improve the scale's accuracy, and we also have to examine detailed discriminant validity controlling for factors such as age and sex.