The Zurich Study. VII. Insomnia: symptoms, classification and prevalence.

This study describes sleep behaviour and insomnia in a representative cohort of a Swiss population. Interviews were carried out prospectively from age 20-21 to 27-28 years, starting with 292 males and 299 females. Females usually go to bed earlier and sleep 30 min longer than males. Taking into account length and periodicity of insomnia we can distinguish occasional insomnia (OI), repeated brief insomnia (RBI), and continued insomnia (CI), defined by operational criteria. The prevalence of sleep problems is stable from age 21-28, at 36%-40%. CI (prevalence 8%-10%) and RBI (13%-19%) are both medical problems in terms of treatment by professionals (10%-17%) or self-medication (7%-12%). The majority of insomniacs cope with sleep problems in various other ways. Frequency and patterns of symptoms of insomnia are described.