Over 600 adult subjects (aged 20–79) were asked to keep a day-by-day record of their hours of sleep on sleep charts for a period of 56 days. When completed the charts gave details of the duration of sleep, the times of falling asleep and awakening, the number and duration of nocturnal disturbances of sleep and the number and duration of mid-day naps. A sample of 240 subjects (20 males and 20 females in each decade from the 20s to the 70s inclusive) was made consisting only of people who recorded for 50 or more days. These subjects were matched, as far as possible, in terms of neuroticism, temperament and intelligence.

It was found that although the average amount of sleep taken per day declined slightly from the 20s to the 50s, there was an increase in the 60s. This was partly due to an increase in the number of mid-day naps taken. The extraverts slept longer than the introverts. The incidence of nocturnal disturbances increased with advancing age, especially in females. These and other findings are discussed and it is suggested that in later years, when social and occupational pressures are reduced, there is a tendency for a polycyclic sleep—wakefulness pattern to reappear.