Lela McKnight-Eily, Ph.D., and her colleagues, all of the CDC’s National Center for Chronic Disease Prevention and Health Promotion, used data from the 2007 national Youth Risk Behavior Survey of 12,154 U.S. high school students, a biennial self-administered survey designed to produce data representative of public and private school students in grades 9 through 12. They assessed hours of sleep by asking students, “On an average school night, how many hours of sleep do you get?” Responses were dichotomized into “insufficient sleep” (fewer than eight hours) and “sufficient sleep” (eight or more hours).