Insomnia Severity Index (ISI)

The Insomnia Severity Index is a brief seven-item questionnaire that rates how severe a person's insomnia has been over the past two weeks.

Each item is scored from zero to four and covers difficulty falling asleep, difficulty staying asleep, waking too early, satisfaction with sleep, how noticeable the problem is to others, how much it worries the person, and how much it interferes with daily functioning. The total ranges from zero to 28, and conventional bands describe no clinically significant insomnia, subthreshold insomnia, moderate insomnia and severe insomnia. Because it takes only a few minutes, the ISI is used in primary care, sleep clinics and research as a screening tool and as a way to track change after a treatment such as cognitive behavioral therapy for insomnia.

The ISI measures the person's own perception rather than objective sleep, so it complements tools such as actigraphy, polysomnography and sleep diaries rather than replacing them. It differs from the Pittsburgh Sleep Quality Index, which covers a month and broader sleep quality, and from the Epworth Sleepiness Scale, which measures daytime sleepiness. Readers encounter the ISI in cannabinoid sleep studies, where it is a common primary outcome. Those studies are small and short so far, and no cannabinoid has an approved use for insomnia.