ISI: The Insomnia Severity Index

What is the Insomnia Severity Index?

The Insomnia Severity Index (ISI) is a 7-item self-report questionnaire developed by Charles M. Morin to measure the severity of insomnia and its impact on daily life. It is the most widely used brief insomnia measure in both clinical practice and treatment research.

The ISI goes beyond simply asking how well someone sleeps. It captures the three classic insomnia complaints — difficulty falling asleep, difficulty staying asleep, and early-morning awakening — alongside satisfaction with sleep, how noticeable the problem is to others, how distressing it feels, and how much it interferes with daytime functioning. That breadth makes a single short score a reasonable summary of the whole insomnia picture.

The ISI takes about five minutes to complete and is freely available for clinical and research use. It asks the respondent to reflect on the past two weeks.

What the ISI Measures

1. Severity of difficulty falling asleep
2. Severity of difficulty staying asleep
3. Severity of early-morning awakening
4. Satisfaction with current sleep pattern
5. How noticeable the sleep problem is to others
6. How worried or distressed the sleep problem is
7. How much the sleep problem interferes with daily functioning

ISI Scoring

Each of the 7 items is rated on a 5-point scale from 0 to 4, and the seven items are summed for a total score ranging from 0 to 28. Higher scores indicate more severe insomnia. No items are reverse-scored.

ISI Severity Bands

The total score is grouped into four bands. These are the interpretation guidelines offered by the measure's developers and are widely used in practice.

The ISI is a severity measure, not a diagnostic instrument. The developers note that the cut-off scores were proposed as practical guidelines — read a single score in the context of the client's history, presentation, and trajectory over time.

Clinical Applications

Insomnia rarely travels alone. It is woven through depression, anxiety, PTSD, chronic pain, and substance use — sometimes as a symptom, sometimes as a driver, often as both. A five-minute ISI gives the clinician a clean read on sleep severity regardless of the primary diagnosis, and surfaces a problem that clients often don't raise on their own.

The ISI was explicitly designed and validated as a treatment-outcome measure. It is sensitive to change, which makes it well suited to tracking response to cognitive behavioral therapy for insomnia (CBT-I), sleep-focused interventions, or the sleep effects of treating a co-occurring condition. Plotting ISI scores across treatment shows whether sleep is genuinely improving or simply being talked about.

Because the recall window is two weeks, the ISI works well on a roughly monthly cadence — frequent enough to track progress, spaced enough that a score reflects a real pattern rather than a couple of bad nights.

Reliability & Validity

The ISI shows strong internal consistency, with Cronbach's alpha around 0.90 in clinical samples, and good convergent validity against sleep diaries and polysomnographic measures. It reliably distinguishes people with insomnia from good sleepers and is responsive to the changes produced by insomnia treatment.

Both clinician and self-report versions exist, and the measure has been validated across clinical, community, and primary-care populations and translated into many languages. Its brevity, sensitivity to change, and well-established interpretation bands are why the ISI is the default brief insomnia measure in most outcome-focused practices.