Psychometric Evaluation of Daytime Sleepiness and Nocturnal Sleep Onset Scales in a Representative Community Sample Eric O. Johnson, Naomi Breslau, Thomas Roth, Timothy Roehrs, and Leon Rosenthal Background: The public health importance of daytime sleepiness as a risk factor for accidents, interpersonal problems, and decreased productivity has been recog- nized. However, epidemiologic research on this topic has been limited by the reliance on laboratory measures (i.e., the Multiple Sleep Latency Test—MSLT). Two scales, daytime sleepiness and nocturnal sleep onset, have been identified from the self-report Sleep–Wake Activity Inven- tory (SWAI) in a clinic sample and validated against the MSLT. This study evaluates the replicability of the two scales in a population sample and assesses potential thresholds in scale scores that distinguish normal from pathologic levels of daytime sleepiness and difficulty falling asleep. Methods: The sample consisted of 2181 subjects 18 – 45 years old in the Detroit metropolitan area. All sleep characteristic information covered the 2 weeks prior to interview. Split-half sample factor analyses were con- ducted to assess replicability of the results. Distribution of scale scores and their relation to construct validity vari- ables were used to evaluate possible thresholds. Results: A two-factor model appeared to best account for the variation among the 12 items from the SWAI. The two factors accounted for 50% of the variance in both split- half sample analyses. The revised eight-item daytime sleepiness and two-item nocturnal sleep onset scales showed good and fair internal consistency respectively across both split-half samples. There appeared to be a “natural break” in daytime sleepiness scale scores that was associated with a substantial and consistent change in number of hours slept. No breaks appeared in nocturnal sleep onset scores. Conclusions: This study replicated the results of the clinic-based study and suggested a potentially useful diagnostic threshold for self-report excessive daytime sleepiness. Epidemiology of sleep depends on the ability to move from the laboratory to population surveys in reliable and valid ways. Development of self-report is a step in that direction. Biol Psychiatry 1999;45:764 –770 © 1999 So- ciety of Biological Psychiatry Key Words: Daytime sleepiness, sleep problems, Sleep– Wake Activity Inventory Introduction A lthough everyone experiences occasional daytime sleepiness resulting from insufficient sleep, the clin- ical and public health importance of chronic excessive daytime sleepiness has been increasingly recognized. Ex- cessive daytime sleepiness has been associated with in- creased risk of motor vehicle and industrial accidents, decreased productivity, and interpersonal problems (Roth et al 1989). In spite of growing public health concerns about the effects of excessive daytime sleepiness, there has been little epidemiologic research on its prevalence and etiol- ogy in the U.S. population. Several community-based studies of Scandinavian populations have been done. In a study of the Finnish population, 11% of women and 7% of men reported daytime sleepiness almost every day (Hublin et al 1996). In another survey, of a large area of Sweden, insufficient sleep was the focus of the questions, and 12% of the respondents felt their sleep was insufficient— leading to daytime sleepiness (Broman et al 1996). How- ever, none of the community-based studies have used validated self-report measures of excessive daytime sleep- iness. Indeed, one reason for the scarcity of epidemiologic studies has been the need to rely on laboratory measures for valid estimates of excessive daytime sleepiness. Spe- cifically, the Multiple Sleep Latency Test (MSLT), which measures time to sleep by a polysomnogram at 2-hour intervals throughout the day following a forced 8 hours in From the Department of Psychiatry and the Sleep Disorder Center, Henry Ford Health Sciences Center, Detroit, Michigan (EOJ, NB, TRoth, TRoehrs, LR); Department of Psychiatry, Case Western Reserve University School of Medi- cine, Cleveland, Ohio (NB); and Department of Psychiatry, University of Michigan School of Medicine, Ann Arbor, Michigan (NB, TRoth). Address reprint requests to Eric O. Johnson, PhD, Henry Ford Health Sciences Center, Department of Psychiatry, 1 Ford Place, 3a, Detroit, MI 48202-3450. Received July 22, 1997; revised January 12, 1998; revised February 19, 1998; accepted February 23, 1998. © 1999 Society of Biological Psychiatry 0006-3223/99/$19.00 PII S0006-3223(98)00111-5