The health impact of disordered breathing during sleep among middle-aged and older men and women in the general population had not been well studied, and the need for treating relatively mild degrees of sleep-disordered breathing was unknown in 1994. The study was the first population study which examined the effect of sleep-disordered breathing on these health outcomes. The study sought to establish the prevalence of clinically important sleep-disordered breathing among middle-aged and older men and women and to provide quantitative data to serve as the basis for selecting patients for screening and deciding which patients might benefit from therapeutic intervention.