Evolution of insomnia: current status and future direction.

Traditional epidemiologic studies of insomnia provide valid but fairly rudimentary information regarding the presence, frequency, duration and evolution of sleep problems. Standardized tools such as validated questionnaires (e.g., Pittsburgh Sleep Quality Index and sleep logs) help assess the presence and severity of sleep problems, while other methods (e.g., SLEEP L system) address insomnia diagnoses. Other instruments (e.g., Structured Clinical Interview for DSM-IV [SCID], Short-Form 36 [SF-36], Epworth Sleepiness Scale [ESS]) provide insights into insomnia consequences and co-morbidities. Sleep laboratory studies using polysomnography (PSG) have also provided useful findings (e.g., relating to sleep apnea and excessive daytime sleepiness) in experimental and population-based patient samples containing subgroups enriched for certain variables under investigation. These methods have significantly increased our knowledge about insomnia. Critically, longitudinal studies are needed to further our understanding of the pathophysiology and morbidity of insomnia, defining roles for risk factors, hyperarousal and co-morbidities and the effects of treatment in long-term disease progression. This review summarizes the current available data on the evolution of insomnia and proposes a model that warrants further research attention and discussion.