occupations ranging from manufacturing to public administration found that the percent of workers who reported a sleep duration of 6 hours or less per night increased from 24 to 30%(4) in the last 20 years. These findings probably demonstrate the development of widespread partial sleep deprivation or sleep "restriction" which is most likely related to external environmental or social factor(s) such as the need to work more than one job or longer work shifts rather than a biologic change in need for sleep. The important question is the extent to which such changes produce negative consequences for performance, health, and/or quality of life.
Much research investigating sleep duration requirements has examined reduced sleep duration because, as evidenced above, chronic or long-standing sleep restriction is increasingly pervasive in the community. Studies of short sleep duration have shown that this "restricted" sleep can be associated with increased sleepiness, poor performance, and increased health risks or mortality.
One way that researchers examine the effect of restricted sleep time, is by having individuals with a given (presumably "normal") sleep duration, usually 7 - 8 hours, sleep for shorter intervals, such as 2 - 7 hours for one or more nights. A common type of research examines changes in performance of specific tasks following normal sleep duration and compares it to performance after a period of sleep restriction. Another type of research employs health surveys or questionnaires that are given to many individuals and which ask about sleep duration and other health characteristics and outcomes. Associations between these features and naturally occurring differences in sleep duration across the study participants are determined by established statistical methods.
Investigators have measured various aspects of performance after sleep duration has been decreased from 8 hours to 7 hours or less for one or more nights. For example, one study showed that participants were significantly more sleepy on the day following reduction of time in bed from 8 to 6 hours (5). Other studies have shown increased sleepiness and delayed response time (similar to taking longer to apply the brakes when trying to stop a car) when